0000950170-23-009201 | 10-K | XBRL Viewer

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Investments - Summary of Available-for-Sale Classified Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Marketable Securities [Line Items]
Cost Basis	$ 47,093	$ 1,011
Accumulated Unrealized Gains	32
Accumulated Unrealized Losses		(1)
Fair Value	47,125	1,010
Commercial Paper
Marketable Securities [Line Items]
Cost Basis	16,741
Fair Value	16,741
Corporate Debt Securities
Marketable Securities [Line Items]
Cost Basis		1,011
Accumulated Unrealized Losses		(1)
Fair Value		$ 1,010
United States Treasury securities
Marketable Securities [Line Items]
Cost Basis	15,768
Accumulated Unrealized Gains	7
Fair Value	15,775
United States Government Agency securitites
Marketable Securities [Line Items]
Cost Basis	14,584
Accumulated Unrealized Gains	25
Fair Value	$ 14,609

Investments

12 Months Ended

Dec. 31, 2022

Investments, Debt and Equity Securities [Abstract]

Investments

4. Investments

Cash in excess of the Company’s immediate requirements is invested in accordance with the Company’s investment policy that primarily seeks to maintain adequate liquidity and preserve capital.

A summary of the Company’s available-for-sale classified investments as of December 31, 2021 and 2022 consisted of the following (in thousands):


	At December 31, 2021
Investments - Current:	Cost Basis		Accumulated Unrealized Gains		Accumulated Unrealized Losses			Fair Value
Corporate debt securities	$	1,011	$	-	$	(1	)	$	1,010
Total	$	1,011	$	-	$	(1	)	$	1,010


	At December 31, 2022
Investments - Current:	Cost Basis		Accumulated Unrealized Gains		Accumulated Unrealized Losses		Fair Value
Commercial paper	$	16,741	$	-	$	-	$	16,741
United States Treasury securities		15,768		7		-		15,775
United States Government Agency securities		14,584		25		-		14,609
Total	$	47,093	$	32	$	-	$	47,125

The amortized cost and fair value of the Company’s available-for-sale investments, by contract maturity, as of December 31, 2022 consisted of the following (in thousands):


	Amortized Cost		Fair Value
Due in one year or less	$	47,093	$	47,125
Total	$	47,093	$	47,125

Commitments and Contingencies - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jul. 30, 2021	Dec. 31, 2022	Dec. 31, 2021
Commitments And Contingencies [Line Items]
Operating leases rent expense		$ 500,000	$ 500,000
Restricted cash		182,000	182,000
Short-term lease asset		566,000	410,000
Short-term lease liability		567,000	476,000
Operating sublease term	12 months
Short-term Leases Recognized on Straight-line Basis
Commitments And Contingencies [Line Items]
Short-term lease asset		0
Short-term lease liability		0
Letter of Credit
Commitments And Contingencies [Line Items]
Restricted cash		$ 182,000	$ 182,000
Lexington, Massachusetts
Commitments And Contingencies [Line Items]
Operating leases expiration date		Dec. 31, 2022
Burlington, Massachusetts
Commitments And Contingencies [Line Items]
Operating leases expiration date		Nov. 30, 2023
Burlington, Massachusetts \| Letter of Credit \| Lease Agreement Require Standby Letter of Credit
Commitments And Contingencies [Line Items]
Restricted cash		$ 182,000

Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2022	Mar. 21, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Trading Symbol	SCPH
Entity Registrant Name	SCPHARMACEUTICALS INC.
Entity Central Index Key	0001604950
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common stock, par value $0.0001
Security Exchange Name	NASDAQ
Entity File Number	001-38293
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-5184075
Entity Address, Address Line One	2400 District Avenue
Entity Address, Address Line Two	Suite 310
Entity Address, City or Town	Burlington
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01803
City Area Code	617
Local Phone Number	517-0730
Document Annual Report	true
Document Transition Report	false
Auditor Name	RSM US LLP
Auditor Location	Boston, Massachusetts
Auditor Firm ID	49
Entity Common Stock, Shares Outstanding		35,769,073
Entity Public Float			$ 75,626,427
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s definitive proxy statement relating to its 2023 annual meeting of stockholders are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. The registrant’s definitive proxy statement will be filed with the U.S. Securities and Exchange Commission within 120 days after the end of the fiscal year ended December 31, 2022.

Accrued Expenses

12 Months Ended

Dec. 31, 2022

Accrued Liabilities, Current [Abstract]

Accrued Expenses

7. Accrued Expenses

Accrued expenses at December 31, 2021 and 2022 consist of (in thousands):


	2021		2022
Employee compensation and related costs	$	1,152	$	2,754
Contract research and development		2,350		1,827
Consulting and professional service fees		265		603
State taxes		5		49
Financing related costs		60		29
Interest		154		16
Other		9		11
Total accrued expenses	$	3,995	$	5,289

Income Taxes - Schedule of Components of Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Federal net operating loss carryforwards	$ 17,252	$ 12,813
State net operating loss carryforwards	4,585	3,630
Research and development tax credits	4,214	3,719
Accrued liabilities	677	327
Stock-based compensation	1,329	1,087
Depreciation and amortization	324	247
Capitalized research and development costs	30,976	29,529
Lease liabilities	146	129
Other		29
Total deferred tax assets	59,503	51,510
Deferred tax liabilities:
Right-of-use lease assets	(144)	(111)
Other	(273)
Total deferred tax liabilities	(417)	(111)
Valuation allowance	(59,086)	(51,399)
Net deferred tax assets	$ 0	$ 0

Fair Value of Financial Instruments

12 Months Ended

Dec. 31, 2022

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments

9. Fair Value of Financial Instruments

The FASB ASC Topic, Fair Value Measurements and Disclosures (“ASC 820”), provides a fair value hierarchy, which classifies fair value measurements based on the inputs used in measuring fair value. Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments and is not a measure of the investment credit quality. The three levels of the fair value hierarchy are described below:

Level 1—Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.

Level 2—Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly.

Level 3—Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and observable.

To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

The carrying values of the Company’s cash and restricted cash, prepaid expenses and deposits approximate their fair values due to their short-term nature. The carrying value of the Company’s term loan payable was considered a reasonable estimate of fair value because the Company’s interest rate is near current market rates for instruments with similar characteristics.

The following tables summarize the Company’s assets and liabilities that are measured at fair value on a recurring basis and indicates the level of the fair value hierarchy utilized to determine such fair values (in thousands):


	As of December 31, 2021
	TOTAL		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	$	72,449	$	72,449	$	—	$	—
Total cash equivalents		72,449		72,449		—		—

Corporate debt securities		1,010		—		1,010		—
Investments		1,010		—		1,010		—

Total	$	73,459	$	72,449	$	1,010	$	—


	As of December 31, 2022
	TOTAL		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	$	65,875	$	65,875	$	—	$	—
Total cash equivalents		65,875		65,875		—		—

Commercial Paper		16,741		—		16,741		—
United States Treasury securities		15,775		15,775		—		—
United States Government Agency securities		14,609		—		14,609		—
Investments		47,125		15,775		31,350		—

Total	$	113,000	$	81,650	$	31,350	$	—
Liabilities:
Derivative liability	$	7,517	$	—	$	—	$	7,517

Total	$	7,517	$	—	$	—	$	7,517

Changes in the fair value of the Company’s Level 3 derivative liability for the year ended December 31, 2022 are as follows:


At December 31, 2021	$	—
Initial fair value of derivative liability		8,852
Change in fair value of derivative liability		(1,335	)
At December 31, 2022	$	7,517

The Oaktree Agreement contains embedded derivatives requiring bifurcation as a derivative instrument. The derivative liability related to the term loan is recorded and accounted for separately in the consolidated financial statements as one compound derivative liability, see Note 10 for additional details. The fair value of the embedded derivative liabilities associated with the term loan was estimated using a hybrid between the discounted cash flow and Monte Carlo simulation methods. This involves significant Level 3 inputs and assumptions including (i) the estimated probability and timing of a change in control and (2) the probability-weighted net sales of FUROSCIX.

A summary of quantitative information about significant unobservable inputs (Level 3 inputs) used in measuring the Company's derivative liability that are categorized within Level 3 of the fair value hierarchy is as follows:


	October 13, 2022	December 31, 2022
Net sales discount rate	23.3%	22.3%
Net sales volatility	80.0%	80.0%
Risk-free rate	4.2%	4.0%
Recovery rate	80.0%	80.0%

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Significant Accounting Policies - Schedule of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 71,061	$ 74,268
Restricted cash	182	182
Cash, cash equivalents and restricted cash	$ 71,243	$ 74,450	$ 72,001

Significant Accounting Policies

12 Months Ended

Dec. 31, 2022

Accounting Policies [Abstract]

Significant Accounting Policies

2. Significant Accounting Policies

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. Significant items subject to such estimates and assumptions include the determination of fair value of financial instruments, accruals related to development costs and clinical activities, and the establishment of the tax valuation allowance. Actual results could differ from those estimates.

Foreign Currency Transactions

The functional currency of the Company is the U.S. dollar. Accordingly, gains and losses resulting from translating transactions denominated in currencies and balances of assets and liabilities outstanding at the balance sheet date, other than U.S. dollars, are included in net loss in the Statements of Operations and Comprehensive Loss.

Cash, Cash Equivalents and Restricted Cash

Cash, cash equivalents and restricted cash consists of bank deposits, certificates of deposit and money market accounts with financial institutions. Cash equivalents are carried at cost which approximates fair value due to their short-term nature and which the Company believes do not have a material exposure to credit risk. The Company considers all highly liquid investments with maturities of three months or less from the date of purchase to be cash equivalents. The Company places its cash and cash equivalents with institutions with high credit quality. However, at certain times such cash and cash equivalents may be in excess of Federal Deposit Insurance Corporation and Securities Investor Protection Corporation insurance limits. The Company has not experienced any losses with respect to these accounts.

As of December 31, 2021 and 2022, the Company classified $182,000 as restricted cash related to a letter of credit issued as a security deposit in connection with the Company’s lease of its corporate office facilities (Note 13). Cash, cash equivalents and restricted cash consists of the following (in thousands):


	December 31, 2021		December 31, 2022
Cash and cash equivalents	$	74,268	$	71,061
Restricted cash		182		182
Cash, cash equivalents and restricted cash	$	74,450	$	71,243

Concentration of Credit Risk

Financial instruments that subject the Company to credit risk primarily consist of cash and cash equivalents and short-term investments. The Company maintains its cash and cash equivalent balances with high-quality financial institutions and, consequently, the Company believes that such funds are subject to minimal credit risk. The Company’s short-term investments consist of commercial paper, United States Treasury securities and United States Government Agency securities. The Company has adopted an investment policy that limits the amounts the Company may invest in any one type of investment and requires all investments held by the Company to hold a minimum rating, thereby reducing credit risk exposure.

Investments

The Company invests excess cash balances in available-for-sale debt securities. The Company determines the appropriate classification of these securities at the time they are acquired and evaluates the appropriateness of such classifications at each balance sheet date. The Company reports available-for-sale investments at fair value at each balance sheet date and includes any unrealized gains and losses in accumulated other comprehensive income (loss), a component of stockholders’ equity. Realized gains and losses are determined using the specific identification method and are included in other income (expense). If any adjustment to fair value reflects a decline in the value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other than temporary,” including the intention to sell and, if so, marks the investment to market through a charge to the Company’s consolidated statements of operations and comprehensive loss.

Inventory

Inventory is stated at the lower of cost and net realizable value and consists of raw materials, work-in-process and finished goods. The Company began capitalizing inventory costs following U.S. Food and Drug Administration ("FDA") approval of FUROSCIX on October 7, 2022. Inventory is sold on a first in, first out ("FIFO") basis. The Company periodically reviews inventory for expiry and obsolescence and writes it down accordingly, if necessary.

Prior to FDA approval of FUROSCIX, the Company expensed all inventory-related costs, including that used for clinical development, to research and development ("R&D") costs in the period incurred.

Leases

The Company determines if an arrangement is a lease at inception. Operating leases are included in right-of-use (“ROU”) lease assets, current portion of lease obligations, and long term lease obligations on the Company’s balance sheets.

ROU lease assets represent the Company’s right to use an underlying asset for the lease term and lease obligations represent the Company’s obligation to make lease payments arising from the lease. Operating ROU lease assets and obligations are recognized at the commencement date based on the present value of lease payments over the lease term. As most of the Company’s leases do not provide an implicit rate, the Company uses its incremental borrowing rate based on the information available at the commencement date in determining the present value of lease payments. The ROU lease asset excludes lease incentives. The Company’s lease terms include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense for lease payments is recognized on a straight-line basis over the lease term.

Debt Issuance Costs

Debt issuance costs are amortized to interest expense using the effective interest rate method over the term of the debt. Debt issuance costs paid to the lender and third parties are reflected as a discount to the debt in the consolidated balance sheets.

Research and Development Costs

Research and development costs are expensed as incurred. Nonrefundable advance payments, if any, for goods or services used in research and development are initially recorded as an asset and then recognized as an expense as the related goods are delivered or services are performed. Research and development expenses include contract services, consulting, salaries, materials and supplies and overhead.

Income Taxes

The Company accounts for income taxes in accordance with Accounting Standard Codification (“ASC”) 740 Income Taxes (“ASC 740”). Deferred tax assets and liabilities are recorded to reflect the impact of temporary differences between amounts of assets and liabilities for financial reporting purposes and such amounts as measured under enacted tax laws. A valuation allowance is required to offset any net deferred tax assets if, based upon the available evidence, it is more likely than not that some or all of the deferred tax asset will not be realized.

The Company provides reserves for potential payments of tax to various tax authorities related to uncertain tax positions. The tax benefits recorded are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is “more likely than not” to be realized following resolution of any uncertainty related to the tax benefit, assuming that the matter in question will be raised by the tax authorities. Potential interest and penalties associated with such uncertain tax positions are recorded as a component of income tax expense. At December 31, 2021 and 2022, the Company had no such accruals.

Stock-Based Compensation

Stock-based compensation expense for stock options is recognized based on the grant-date fair value using the Black-Scholes valuation model. Restricted stock units are valued at the fair market value per share of the Company’s common stock on the date of grant. The Company recognizes compensation expense only for those stock-based awards expected to vest after considering expected forfeitures. Cumulative compensation expense is at least equal to the compensation expense for vested awards. Stock-based compensation is recognized on a straight-line basis over the service period of each award.

Segments

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker (“CODM”) in making decisions regarding resource allocation and assessing performance. The Company’s chief executive officer is the CODM, and he uses consolidated financial information in determining how to allocate resources and assess performance. The Company has determined that it operates in one segment.

Recently Issued Accounting Standards

In June 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update ("ASU") 2016-13, Financial Instruments-Credit Losses : Measurement of Credit Losses on Financial Instruments ("ASU 2016-13"), which requires the measurement and recognition of expected credit losses for financial assets held at amortized cost. ASU 2016-13 replaces the existing incurred loss impairment model with an expected loss methodology, which will result in more timely recognition of credit losses. The ASU will be effective for the Company's fiscal year beginning January 1, 2023. The Company is currently evaluating the impact of the adoption of ASU 2016-13 and does not expect adoption to have a material effect on the Company’s consolidated financial statements or disclosures.

401(k) Savings Plan	12 Months Ended
401(k) Savings Plan	Dec. 31, 2022
Retirement Benefits [Abstract]
401(k) Savings Plan	14. 401(k) Savings Plan In July 2014, the Company established a defined contribution savings plan under Section 401(k) of the Internal Revenue Code covering all of its employees. Employees may make contributions by withholding a percentage of their salary. The plan includes an employer match equal to 100% on the first 3% of deferred compensation and an additional 50% on the next 2% of deferred compensation. During the years ended December 31, 2021 and 2022, the Company has recognized compensation expense of $198,000 and $340,000, respectively, for the employer match contribution.

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	34,257,916	27,366,707
Common stock, shares outstanding	34,257,916	27,366,707

Fair Value of Financial Instruments - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Liabilities:
Derivative liability	$ 7,517
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	65,875	$ 72,449
Investments	47,125	1,010
Total	113,000	73,459
Liabilities:
Derivative liability	7,517
Total	7,517
Fair Value, Measurements, Recurring \| Corporate Debt Securities
Assets:
Investments		1,010
Fair Value, Measurements, Recurring \| Commercial Paper
Assets:
Investments	16,741
Fair Value, Measurements, Recurring \| United States Treasury securities
Assets:
Investments	15,775
Fair Value, Measurements, Recurring \| United States Government Agency securitites
Assets:
Investments	14,609
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Cash equivalents	65,875	72,449
Investments	15,775
Total	81,650	72,449
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets (Level 1) [Member] \| United States Treasury securities
Assets:
Investments	15,775
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) [Member]
Assets:
Investments	31,350	1,010
Total	31,350	1,010
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) [Member] \| Corporate Debt Securities
Assets:
Investments		$ 1,010
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) [Member] \| Commercial Paper
Assets:
Investments	16,741
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) [Member] \| United States Government Agency securitites
Assets:
Investments	14,609
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3) [Member]
Liabilities:
Derivative liability	7,517
Total	$ 7,517

Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2022 USD ($) Segment	Dec. 31, 2021 USD ($)
Schedule Of Accounting Policies [Line Items]
Restricted cash, current	$ 182,000	$ 182,000
Potential interest and penalties associated with uncertain tax positions, accruals	$ 0	0
Number of operating segments \| Segment	1
Letter of Credit
Schedule Of Accounting Policies [Line Items]
Restricted cash, current	$ 182,000	$ 182,000

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2022

Property, Plant and Equipment [Abstract]

Schedule of Purchased Property and Equipment

Purchased property and equipment consist of the following as of December 31, 2021 and 2022 (in thousands):


	ESTIMATED USEFUL LIFE	2021			2022
Office equipment	5 years	$	10		$	6
Office furniture	7 years		126			126
Computer equipment	3 years		8			15
Leasehold improvements	Life of lease		95			95
			239			242
Less: Accumulated depreciation			(170	)		(188	)
Property and equipment, net		$	69		$	54

Stock-Based Compensation - Summary of Stock Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 2,838	$ 2,366
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	1,050	947
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,788	$ 1,419

Stock-Based Compensation - Schedule of RSU Activity (Details) - Restricted Stock Units (RSUs) - $ / shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
RSUs outstanding	42,250	80,450
RSUs Granted	0	0
RSUs Vested	(42,250)	(38,200)
RSUs Forfeited	0	0
RSUs outstanding	0	42,250
AVERAGE GRANT DATE FAIR VALUE, Outstanding	$ 3.25	$ 3.25
AVERAGE GRANT DATE FAIR VALUE, Granted	0	0
AVERAGE GRANT DATE FAIR VALUE, Vested	3.25	3.25
AVERAGE GRANT DATE FAIR VALUE, Forfeited	0	0
AVERAGE GRANT DATE FAIR VALUE, RSUs outstanding	$ 0	$ 3.25

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
Consolidated Statements of Cash Flows - USD ($)	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities
Net loss	$ (36,838,000)	$ (28,034,000)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation expense	37,000	34,000
Amortization expense - right-of-use leased assets - operating	431,000	404,000
Accretion on short-term investments	(244,000)	124,000
Stock-based compensation	2,838,000	2,366,000
Non-cash interest expense	884,000	554,000
Fair value adjustment to derivative liability	(1,335,000)
Changes in operating assets and liabilities
Inventory	(1,230,000)
Prepaid expenses and other assets	(887,000)	(234,000)
Accounts payable, accrued expenses and other liabilities	1,767,000	(2,365,000)
Net cash flows used in operating activities	(34,577,000)	(27,151,000)
Cash flows from investing activities
Purchases of property and equipment	(21,000)	(9,000)
Maturities of short-term investments	21,700,000	41,150,000
Purchases of short-term investments	(67,538,000)	(9,011,000)
Net cash flows provided by (used in) investing activities	(45,859,000)	32,130,000
Cash flows from financing activities
Proceeds from common stock offering, net of underwriter discounts and offering costs	46,645,000
Proceeds from at-the-market offering, net	1,120,000
Proceeds from the exercise of stock options	44,000	9,000
Proceeds from employee stock purchase plan	173,000	42,000
Proceeds from term loan	47,301,000
Principal payments on term loan	(17,500,000)	(2,500,000)
Payment Of Term Loan Final Fee	(500,000)
Settlement of restricted stock units for tax withholding obligations	(54,000)	(81,000)
Net cash flows (used in) provided by financing activities	77,229,000	(2,530,000)
Net increase (decrease) in cash	(3,207,000)	2,449,000
Cash, cash equivalents and restricted cash, beginning of year	74,450,000	72,001,000
Cash, cash equivalents and restricted cash, end of year	71,243,000	74,450,000
Supplemental cash flow information
Interest paid	2,555,000	2,043,000
Taxes paid	190,000	$ 206,000
Supplemental disclosure of non-cash activities
Transfer of issuance costs from other noncurrent assets to equity	$ 6,000

Stockholders' Equity - Additional Information (Details) - USD ($)			1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 01, 2023	Mar. 23, 2021	Nov. 30, 2022	Mar. 22, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Stockholders Equity Note [Line Items]
Common stock, shares authorized					150,000,000	150,000,000
Common stock, par value					$ 0.0001	$ 0.0001
Common stock, shares issued					34,257,916	27,366,707
Common stock, shares outstanding					34,257,916	27,366,707
Reserved shares of common stock for exercise of outstanding options to purchase common stock					4,008,177	2,662,752	2,224,913
Preferred stock, shares authorized					10,000,000	10,000,000
Preferred stock, par value					$ 0.0001	$ 0.0001
Preferred stock, shares issued					0	0
Preferred stock, shares outstanding					0	0
prefunded warrant purchase price					$ 0.001
Cowen \| Common Stock \| Maximum
Stockholders Equity Note [Line Items]
Aggregate offering price					$ 48,900,000
2021 ATM Agreement
Stockholders Equity Note [Line Items]
Number of shares sold	1,511,157
Selling price per share	$ 9.30
Proceeds from sale of shares, Net				$ 13,700,000
2021 ATM Agreement \| Legal Accounting and Other Costs
Stockholders Equity Note [Line Items]
Stock issuance cost		$ 273,000
2021 ATM Agreement \| Additional Paid-in Capital \| Legal Accounting and Other Costs
Stockholders Equity Note [Line Items]
Stock issuance cost					$ 6,000
2021 ATM Agreement \| Cowen \| Common Stock
Stockholders Equity Note [Line Items]
Number of shares sold					181,553
Proceeds from sale of shares, Net					$ 1,100,000
2021 ATM Agreement \| Cowen \| Common Stock \| Weighted Average
Stockholders Equity Note [Line Items]
Selling price per share					$ 6.33
2021 ATM Agreement \| Cowen \| Common Stock \| Maximum
Stockholders Equity Note [Line Items]
Aggregate offering price		$ 50,000,000.0
Percentage of commission on gross sales proceeds		3.00%
Underwritten Public Offering \| Common Stock
Stockholders Equity Note [Line Items]
Number of shares sold			6,620,000
Selling price per share			$ 5.25
Proceeds from sale of shares, Net			$ 46,600,000
prefunded warrant purchase price			$ 5.249
Underwritten Public Offering \| Common Stock \| Maximum
Stockholders Equity Note [Line Items]
prefunded warrant shares			2,905,000

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Accrued Liabilities, Current [Abstract]
Employee compensation and related costs	$ 2,754	$ 1,152
Contract research and development	1,827	2,350
Consulting and professional service fees	603	265
State taxes	49	5
Financing related costs	29	60
Interest	16	154
Other	11	9
Total accrued expenses	$ 5,289	$ 3,995

Commitments and Contingencies

12 Months Ended

Dec. 31, 2022

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

13. Commitments and Contingencies

Operating Leases

The Company entered into noncancelable operating leases for office facilities located in Lexington, Massachusetts and Burlington, Massachusetts through December 31, 2022 and November 30, 2023, respectively. Rent expense under the operating leases totaled $0.5 million and $0.5 million for the years ended December 31, 2021 and 2022, respectively.

Certain leases provide for increases in future minimum annual rental payments as defined in the lease agreements. The leases generally also include real estate taxes and common area maintenance charges in the annual rental payments.

Pursuant to the terms of its lease agreement for the Company’s headquarters in Burlington, Massachusetts, the Company obtained a letter of credit in the amount of approximately $182,000 as security on the lease obligation. The letter of credit is listed as restricted cash on the Company’s consolidated balance sheets.

Short-term leases are leases having a term of twelve months or less. The Company recognizes short-term leases on a straight-line basis and does not record a related lease asset or liability for such leases.

The following is a maturity analysis of the annual undiscounted cash flows reconciled to the carrying value of the operating lease liabilities as of December 31, 2022 (in thousands):


Year ended:
December 31, 2023	$	596
December 31, 2024		9
December 31, 2025		1
Total minimum lease payments		606
Less imputed interest		(32	)
Total	$	574


	2021			2022
Lease cost:
Operating lease cost	$	482		$	505
Short-term lease cost		20			37
Sublease income		(51	)		(47	)
Total lease cost	$	451		$	495
Other information
Cash paid for amounts included in the measurement of liabilities	$	530		$	551
Operating cash flows from operating leases	$	(60	)	$	(57	)
Weighted-average remaining lease term - operating leases	0.9 years			0.9 years
Weighted-average discount rate - operating leases		10.1	%		10.1	%

In July 2021, the Company signed a lease agreement for a new office facility located in Salem, New Hampshire. The lease commenced on September 1, 2021 and had an initial term of 12 months with an optional extension term through August 2023. In June 2022, the Company exercised the lease option. The lease is considered short-term and is being recognized on a straight-line basis.

Research and Development Agreements

As part of the Company’s research and development efforts, the Company enters into research and development agreements with unrelated companies. These agreements contain varying terms and provisions which include fees and milestones to be paid by the Company. Some of these agreements also contain provisions which require the Company to make payments for exclusivity in the development of products in the area of loop diuretics.

Contingencies

The Company follows subtopic 450-20 of the FASB ASC to report accounting for contingencies.

Certain conditions may exist as of the date the financial statements are issued, which may result in a loss to the Company but which will only be resolved when one or more future events occur or fail to occur. The Company assesses such contingent liabilities, and such assessment inherently involves an exercise of judgment.

If the assessment of a contingency indicates that it is probable that a material loss has been incurred and the amount of the liability can be estimated, then the estimated liability would be accrued in the Company’s financial statements. If the assessment indicates that a potential material loss contingency is not probable but is reasonably possible, or is probable but cannot be estimated, then the nature of the contingent liability, and an estimate of the range of possible losses, if determinable and material, would be disclosed. Loss contingencies considered remote are generally not disclosed unless they involve guarantees, in which case the guarantees would be disclosed.

Due to the discontinuation of use of the first generation device in 2019, the Company has received notice of termination costs related to the program. Certain of the Company’s vendors have claimed or billed for additional costs for which the Company believes it is not obligated. The Company has evaluated this contingent liability in accordance with ASC 450, Contingencies, and determined that the possibility of additional costs is remote and no longer probable.

Net Loss per Share - Additional Information (Details)	Dec. 31, 2022 $ / shares
Earnings Per Share [Abstract]
Exercise price per share	$ 0.001

Debt - Schedule of Future Principal Payments Due (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Sep. 30, 2019
Debt Instrument [Line Items]
Total minimum principal payments	$ 50,000	$ 17,500
2019 Loan Agreement \| SLR Investment Corp. and Silicon Valley Bank
Debt Instrument [Line Items]
December 31, 2025	2,500
December 31, 2026	10,000
December 31, 2027	37,500
Total minimum principal payments	$ 50,000		$ 20,000

Description of Business and Basis of Presentation

12 Months Ended

Dec. 31, 2022

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Description of Business and Basis of Presentation

1. Description of Business and Basis of Presentation

Description of Business

scPharmaceuticals LLC was formed as a Limited Liability Company under the laws of the State of Delaware on February 19, 2013. On March 24, 2014, scPharmaceuticals LLC was converted to a Delaware Corporation and changed its name to scPharmaceuticals Inc. (“the Company”). The Company is a pharmaceutical company focused on developing and commercializing products that have the potential to optimize the delivery of infused therapies, advance patient care and reduce healthcare costs. The Company’s strategy is designed to enable the subcutaneous administration of therapies that have previously been limited to intravenous (“IV”) delivery. The Company’s headquarters and primary place of business is Burlington, Massachusetts.

Basis of Presentation

The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”) and have been prepared on a basis which assumes that the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities and commitments in the normal course of business. The consolidated financial statements reflect the operations of the Company and its wholly-owned subsidiary, scPharmaceuticals Securities Corporation. All significant intercompany balances and transactions have been eliminated in consolidation.

Liquidity

At December 31, 2022, the Company had cash, cash equivalents, restricted cash and investments of $118.4 million and working capital of $115.9 million. During the year ended December 31, 2022, the Company incurred a net loss totaling $36.8 million and used cash in operating activities totaling $34.6 million. The Company expects to continue to incur losses and use cash in operating activities in 2023.

In October 2022, the Company entered into a Credit Agreement and Guaranty (the "Oaktree Agreement") with, among others, the lenders from time to time party thereto (the "Lenders") and Oaktree Fund Administration, LLC, in its capacity as administrative agent for the Lenders (Note 10). In November 2022, the Company completed an underwritten public offering with net proceeds of $46.6 million (Note 11). In addition, the Company currently has an at-the-market offering program with Cowen and Company, LLC that has $48.9 million in capacity remaining at December 31, 2022 (Note 11).

The Company believes that, based on its current development plans and activities, its resources will be sufficient to satisfy its liquidity requirements for more than one year from the issuance date of these consolidated financial statements.

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Operating expenses:
Research and development	$ 15,533	$ 16,039
General and administrative	20,624	9,784
Total operating expenses	36,157	25,823
Loss from operations	(36,157)	(25,823)
Other income	1,418	315
Interest income	1,203	49
Interest expense	(3,302)	(2,575)
Net loss	$ (36,838)	$ (28,034)
Net loss per share, basic	$ (1.30)	$ (1.02)
Net loss per share, diluted	$ (1.30)	$ (1.02)
Weighted --average common shares outstanding, basic	28,358,502	27,351,730
Weighted--average common shares outstanding, diluted	28,358,502	27,351,730
Other comprehensive loss:
Unrealized (loss) gain on short-term investments	$ 33	$ (2)
Comprehensive loss	$ (36,805)	$ (28,036)

Net Loss per Share

12 Months Ended

Dec. 31, 2022

Earnings Per Share [Abstract]

Net Loss per Share

3. Net Loss per Share

Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period without consideration of dilutive common stock equivalents. Diluted net loss per share is the same as basic net loss per common share, since the effects of potentially dilutive securities are anti-dilutive. Basic and diluted weighted average shares of common stock outstanding for the year ended December 31, 2022 include the weighted average effect of outstanding pre-funded warrants for the purchase of shares of common stock for which the remaining unfunded exercise price is $0.001 per share.

Dilutive common stock equivalents are comprised of unexercised stock options outstanding under the Company’s equity plan, unexercised warrants and unvested restricted stock.

The following table sets forth the computation of basic and diluted net loss per share of common stock (in thousands, except shares and per share data):


	For the year ended
	December 31, 2021			December 31, 2022
Net loss	$	(28,034	)	$	(36,838	)
Weighted—average common shares outstanding, basic and diluted		27,351,730			28,358,502
Net loss per share, basic and diluted	$	(1.02	)	$	(1.30	)

The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because their inclusion would be anti-dilutive (in common stock equivalent shares):


	For the year ended
	December 31, 2021		December 31, 2022
Stock options to purchase common stock		2,662,752		4,008,177
Warrants to purchase common stock		—		516,345
Unvested restricted stock		42,250		—
		2,705,002		4,524,522

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Current assets
Cash and cash equivalents	$ 71,061	$ 74,268
Short-term investments	47,125	1,010
Restricted cash	182	182
Inventory	1,230
Prepaid expenses	2,282	2,791
Deposits and other current assets	1,428	24
Total current assets	123,308	78,275
Property and equipment, net	54	69
Right-of-use lease assets - operating, net	566	410
Deposits and other assets	267	283
Total assets	124,195	79,037
Current liabilities
Accounts payable	1,518	544
Accrued expenses	5,289	3,995
Term loan, short-term		9,805
Lease obligation - operating, short-term	567	476
Other current liabilities	42	26
Total current liabilities	7,416	14,846
Term loan, long-term	36,794	7,354
Derivative liability	7,517
Lease obligation - operating, long-term	7
Other liabilities	28	367
Total liabilities	51,762	22,567
Commitments and contingencies (Note 13)
Stockholders’ Equity
Preferred stock, $0.0001 par value; 10,000,000 shares authorized and no shares issued and outstanding
Common stock; $0.0001 par value; 150,000,000 shares authorized at December 31, 2022; 27,325,959 and 27,366,707 and 34,257,916 shares issued and outstanding at December 31, 2021 and December 31, 2022, respectively	3	3
Additional paid-in capital	298,934	246,166
Accumulated deficit	(226,536)	(189,698)
Accumulated other comprehensive (loss) income	32	(1)
Total stockholders’ equity	72,433	56,470
Total liabilities and stockholders’ equity	$ 124,195	$ 79,037

Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2022

Accounting Policies [Abstract]

Schedule of Cash, Cash Equivalents and Restricted Cash


	December 31, 2021		December 31, 2022
Cash and cash equivalents	$	74,268	$	71,061
Restricted cash		182		182
Cash, cash equivalents and restricted cash	$	74,450	$	71,243

Subsequent Events (Additional Information) (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended
	Feb. 01, 2023	Jan. 01, 2023	Mar. 22, 2023
Subsequent Event [Line Items]
Equity awards granted under the inducement , Granted	500,000
2021 ATM Agreement
Subsequent Event [Line Items]
Number of shares sold		1,511,157
Selling price per share		$ 9.30
Proceeds from sale of shares, Net			$ 13.7

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2022

Earnings Per Share [Abstract]

Computation of Basic and Diluted Net Loss Per Share of Common Stock

The following table sets forth the computation of basic and diluted net loss per share of common stock (in thousands, except shares and per share data):


	For the year ended
	December 31, 2021			December 31, 2022
Net loss	$	(28,034	)	$	(36,838	)
Weighted—average common shares outstanding, basic and diluted		27,351,730			28,358,502
Net loss per share, basic and diluted	$	(1.02	)	$	(1.30	)

Schedule of Antidilutive Securities Excluded from Computation of Net Loss Per Share


	For the year ended
	December 31, 2021		December 31, 2022
Stock options to purchase common stock		2,662,752		4,008,177
Warrants to purchase common stock		—		516,345
Unvested restricted stock		42,250		—
		2,705,002		4,524,522

401(k) Savings Plan - Additional Information (Details) - USD ($)		12 Months Ended
	Jul. 31, 2014	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Contribution Plan Disclosure [Line Items]
Defined Contribution Plan, Tax Status [Extensible List]		us-gaap:QualifiedPlanMember	us-gaap:QualifiedPlanMember	us-gaap:QualifiedPlanMember
Compensation expense for employer match contribution		$ 340,000	$ 198,000
First 3% of Deferred Compensation
Defined Contribution Plan Disclosure [Line Items]
Employer matching contribution percentage	100.00%
Employer matching contribution percentage of employees contributions of deferred compensation	3.00%
Defined Contribution Plan, Tax Status [Extensible List]	us-gaap:QualifiedPlanMember
Next 2% of Deferred Compensation
Defined Contribution Plan Disclosure [Line Items]
Employer matching contribution percentage	50.00%
Employer matching contribution percentage of employees contributions of deferred compensation	2.00%
Defined Contribution Plan, Tax Status [Extensible List]	us-gaap:QualifiedPlanMember

Stockholders' Equity

12 Months Ended

Dec. 31, 2022

Equity [Abstract]

Stockholders' Equity

11. Stockholders’ Equity

Common Stock

At December 31, 2021 and 2022, the Company had 150,000,000 shares of common stock authorized with a par value of $0.0001. There were 27,366,707 and 34,257,916 shares issued and outstanding at December 31, 2021 and 2022, respectively. Voting, dividend and liquidation rights of the holders of the common stock are subject to the Company’s articles of incorporation, corporate bylaws and underlying shareholder agreements.

Reserved Shares

The Company has reserved 4,008,177 shares of common stock for the exercise of outstanding options to purchase common stock.

2021 At-the-Market Issuance Sales Agreement

On March 23, 2021, the Company entered into an Open Market Sale AgreementSM (the “2021 ATM Agreement”) with Cowen and Company, LLC (“Cowen”) with respect to an at-the-market offering program (the “2021 ATM Program”) under which the Company could offer and sell shares of its common stock (the “2021 ATM Shares”), having an aggregate offering price of up to $50.0 million through Cowen as its sales agent. The offering and sale

of 2021 ATM Shares are made pursuant to the Company’s shelf registration statement on Form S-3, which was declared effective by the SEC on April 29, 2021 (the “2021 Registration Statement”).

The Company agreed to pay Cowen a commission up to 3.0% of the gross sales proceeds of such 2021 ATM Shares. The Company incurred $273,000 of legal, accounting, and other costs to establish and activate the 2021 ATM Program.

During the year ended December 31, 2022, the Company sold a total of 181,553 2021 ATM Shares under the 2021 ATM Agreement, in the open market, at a weighted average gross selling price of $6.33 per share for net proceeds of $1.1 million. The Company charged $6,000 in costs related to establishing and activating the program against additional paid in capital upon issuance of shares in 2022.

Sale of Common Stock

In November 2022, the Company completed an underwritten public offering of 6,620,000 shares of its common stock (the “2022 Offering Shares”), pursuant to the 2021 Registration Statement. The 2022 Offering Shares were sold at an offering price of $5.25 per share. In addition, a prefunded warrant to purchase up to 2,905,000 shares of common stock at a purchase price of $5.249 per underlying share was issued as part of the transaction. The pre-funded warrants were accounted for as equity instruments. Net proceeds of the offering were $46.6 million, after deducting underwriting discounts, commissions and offering expenses.

Preferred Stock

At December 31, 2021 and 2022, the Company had 10,000,000 shares of preferred stock authorized with a par value of $0.0001 and no shares of preferred stock were issued or outstanding.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-URI https://asc.fasb.org/topic&trid=2208762

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 14
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496171-112644

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 14
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496171-112644

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI https://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496189-112644

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (g)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496189-112644

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (h)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 14
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496171-112644

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496189-112644

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 16
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496180-112644

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (i)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
-URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 40
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126731327&loc=SL126733271-114008

+ Details

Property and Equipment - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 37,000	$ 34,000

Fair Value of Financial Instruments - Schedule of Quantitative Information about Significant Unobservable Inputs (Details) - Level 3	Dec. 31, 2022	Oct. 13, 2022
Net Sales Discount Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.223	0.233
Net Sales Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.800	0.800
Risk-free Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.040	0.042
Recovery Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.800	0.800

Debt - Additional Information (Details) - USD ($)		1 Months Ended		12 Months Ended
Debt - Additional Information (Details) - USD ($)	Oct. 13, 2022	Sep. 30, 2019	May 31, 2017	Dec. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Loan and security agreement, amount				$ 50,000,000	$ 17,500,000
Proceeds from term loan				$ 47,301,000
Exercise price per share				$ 0.001
Fair market value per share of common stock				$ 3.18	$ 4.18
Unamortized debt discount				$ (13,206,000)	$ (341,000)
Fair value adjustment to derivative liability				$ (1,335,000)
Minimum
Debt Instrument [Line Items]
Expected life				5 years 6 months	5 years 6 months
Maximum
Debt Instrument [Line Items]
Expected life				6 years 8 months 12 days	6 years 8 months 12 days
SLR Investment Corp. and Silicon Valley Bank \| 2017 Loan Agreement
Debt Instrument [Line Items]
Loan and security agreement, amount			$ 10,000,000.0
Loan agreement, maturity date			May 01, 2021
Payment of final fee		$ 325,000
SLR Investment Corp. and Silicon Valley Bank \| 2019 Loan Agreement
Debt Instrument [Line Items]
Loan and security agreement, amount		$ 20,000,000.0		$ 50,000,000
Loan agreement, maturity date		Sep. 17, 2023
Amortization of debt discount				341,000	$ 392,000
Final payment fee				500,000
Amortization of final payment fee				$ 132,000	$ 162,000
Loan agreement, term		4 years
Debt instrument, interest rate terms				The interest rate under the 2019 Loan Agreement was the higher of (i) LIBOR plus 7.95% or (ii) 10.18%
Debt instrument, effective interest rate				10.18%
Exit fee, percentage				4.00%
Exit fee				$ 800,000
Derivative liability recorded against exit fee obligation				763,000
Fair value adjustment to derivative liability				$ 30,000
Prepayment premium percentage after year two				0.50%
Long term debt prepayment premium amount				$ 46,000
SLR Investment Corp. and Silicon Valley Bank \| 2019 Loan Agreement \| Minimum
Debt Instrument [Line Items]
Interest rate, minimum				10.18%
Prepayment premium percentage two				0.01
SLR Investment Corp. and Silicon Valley Bank \| 2019 Loan Agreement \| Maximum
Debt Instrument [Line Items]
Prepayment premium percentage one				0.03
SLR Investment Corp. and Silicon Valley Bank \| 2019 Loan Agreement \| Libor
Debt Instrument [Line Items]
Basis spread on variable base rate				7.95%
Oaktree Agreement [Member]
Debt Instrument [Line Items]
Loan agreement, maturity date	Oct. 13, 2027
Basis spread on variable base rate	8.25%
Proceeds from (Repayments of) Debt, Total	$ 9,800,000
Payment of financing and stock issuance costs	2,700
Long term additional debt discount exit fee				$ 1,000,000.0
Embedded derivative liability upon issuance of Term Loan	8,900,000
Fair value of embedded derivative liability	7,500,000
Amortization of debt discount				383,000
Unamortized debt discount	$ (13,600,000)
Exit fee				$ 28,000,000
Prepayment premium percentage one	0.020
Increase in interest rate on default	2.00%
Oaktree Agreement [Member] \| Minimum
Debt Instrument [Line Items]
Trailing of net sales	$ 100,000,000.0
Oaktree Agreement [Member] \| Maximum
Debt Instrument [Line Items]
Loan and security agreement, amount	$ 100,000,000.0
Oaktree Agreement [Member] \| Warrants
Debt Instrument [Line Items]
Exercise price per share	$ 5.40
Relative fair value of detachable warrants	$ 2,000,000.0
Risk-free rate	4.11%
Expected life	7 years
Fair market value per share of common stock	$ 5.50
Exercise price per warrant	$ 5.40
Expected volatility	77.00%
Oaktree Agreement [Member] \| Warrants \| Maximum
Debt Instrument [Line Items]
Purchase shares of common stock	516,345
Oaktree Agreement [Member] \| SOFR
Debt Instrument [Line Items]
Basis spread on variable base rate	8.75%
Oaktree Agreement [Member] \| SOFR \| Interest Rate Floor [Member]
Debt Instrument [Line Items]
Basis spread on variable base rate	1.00%
Oaktree Agreement [Member] \| SOFR \| Interest Rate Cap [Member]
Debt Instrument [Line Items]
Basis spread on variable base rate	3.00%
Oaktree Agreement [Member] \| Borrowings One [Member]
Debt Instrument [Line Items]
Loan and security agreement, amount	$ 50,000,000.0
Proceeds from term loan	37,500,000
Unrestricted cash	15,000,000.0
Oaktree Agreement [Member] \| Borrowings Two [Member]
Debt Instrument [Line Items]
Loan and security agreement, amount	50,000,000.0
Unrestricted cash	20,000,000.0
Oaktree Agreement [Member] \| Borrowings Three [Member]
Debt Instrument [Line Items]
Loan and security agreement, amount	$ 50,000,000.0

Subsequent Events

12 Months Ended

Dec. 31, 2022

Subsequent Events [Abstract]

Subsequent Events

15. Subsequent Events

The Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the financial statements to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure.

In the period beginning January 1, 2023 through the date of this Annual Report on Form 10-K, the Company issued and sold an additional 1,511,157 shares of its common stock under the 2021 ATM Agreement at a weighted average gross selling price of $9.30 per share for net proceeds of $13.7 million.

On February 1, 2023, the Board of Directors of the Company adopted the 2023 Employment Inducement Award Plan (the "Inducement Plan") and, subject to the adjustment provisions of the Inducement Plan, reserved 500,000 shares of the Company’s Common Stock for issuance pursuant to equity awards granted under the Inducement Plan.

Net Loss per Share - Computation of Basic and Diluted Net Loss Per Share of Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share [Abstract]
Net loss	$ (36,838)	$ (28,034)
Weighted Average Number of Shares Outstanding, Basic	28,358,502	27,351,730
Weighted Average Number of Shares Outstanding, Diluted	28,358,502	27,351,730
Net loss per share, basic	$ (1.30)	$ (1.02)
Net loss per share, diluted	$ (1.30)	$ (1.02)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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Reference 35: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8933-108599

+ Details

Fair Value of Financial Instruments - Schedule of Changes in Fair Value of Level 3 Derivative Liability (Details) - Significant Unobservable Inputs (Level 3) [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Initial fair value of derivative liability	$ 8,852
Change in fair value of derivative liability	$ (1,335)
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Nonoperating Income (Expense)
Ending balance	$ 7,517

Debt

12 Months Ended

Dec. 31, 2022

Debt Disclosure [Abstract]

Debt

10. Debt

The following table presents the carrying value of the Company's debt balance as of December 31, 2021 and 2022 (in thousands):


	DECEMBER 31, 2021			DECEMBER 31, 2022
Face value of term loans	$	17,500		$	50,000
Unamortized debt discount		(341	)		(13,206	)
Total debt, net	$	17,159		$	36,794
Less: short-term debt		(9,805	)		—
Long-term debt	$	7,354		$	36,794

Oaktree Agreement

On October 13, 2022 (“Closing Date”), the Company entered into a Credit Agreement and Guaranty (the “Oaktree Agreement”) with Oaktree Fund Administration, LLC as administrative agent, and the lenders party thereto (collectively “Oaktree”) to borrow up to $100.0 million in three tranches with a maturity date of October 13, 2027.

The first tranche of $50.0 million was drawn immediately, with $9.8 million of the proceeds used to repay in full the outstanding loan and fees under the 2019 Loan Agreement with SLR Investment Corp. and Silicon Valley Bank and $2.7 million in fees and expenses incurred in connection with the financing, leaving $37.5 million in available proceeds from the first tranche. The ability to draw the remaining $50.0 million is contingent upon reaching certain net sales revenue milestone targets prior to September 30, 2024 and December 31, 2024, respectively.

The term loan initially bears interest at the three-month term Secured Overnight Financing Rate (“SOFR”) plus an applicable margin of 8.75% (with a SOFR floor of 1.00% and a 3.00% cap). Once FUROSCIX achieves at least $100.0 million in trailing 12-month net sales, the applicable margin will step down to 8.25%. The Company is required to make quarterly interest-only payments until the third anniversary of the Closing Date, after which the Company is required to make quarterly amortizing payments, with the remaining balance of the principal plus accrued and unpaid interest due at maturity.

In connection with entering into the Oaktree Agreement, the Company granted warrants to Oaktree to purchase up to an aggregate of 516,345 shares of the Company’s common stock at an exercise price of $5.40 per share. Upon inception, the Company evaluated the warrants and determined that they met all the requirements for equity classification under ASC 815. This transaction was accounted for as a detachable warrant at its fair value, using the relative fair value method, which is based on a number of unobservable inputs and is recorded as an increase to additional paid-in-capital on the consolidated statement of stockholder’s equity. The relative fair value of the warrants, $2.0 million, was reflected as a discount to the term loan and will be amortized over the life of the term loan using the effective interest method. The Company used the Black-Scholes option pricing model to determine the fair value of the warrants. Assumptions included the fair market value per share of common stock on the valuation date of $5.50, the exercise price per warrant equal to $5.40, the expected volatility of 77%, the risk-free interest rate of 4.11%, the expected term of 7 years and the absence of a dividend. The warrants are immediately exercisable and the exercise period expires on October 13, 2029.

The Company identified a number of embedded derivatives that require bifurcation from the term loan and that were separately accounted for in the consolidated financial statements as one compound derivative liability. Certain of these embedded features include contingent interest rate reset upon event of default, contingent put options, including change in control and going concern provisions, and additional costs as a result of changes in

law. These embedded features met the criteria requiring these to be bifurcated because they were not clearly and closely related to the host instrument in accordance with ASC 815-15 and the derivative liability is presented separately in the condensed consolidated balance sheet as of December 31, 2022. The fair value of the embedded derivative liabilities associated with the term loan was estimated using a hybrid between the discounted cash flow and Monte Carlo simulation methods. This involves significant Level 3 inputs and assumptions including an estimated probability and timing of a change in control. The Company re-evaluates this assessment each reporting period and any changes in estimated fair value is recorded as other income (expense). The initial recognition of the embedded derivative liability upon issuance of the Term Loan was $8.9 million. At December 31, 2022, the fair value of the embedded derivative liability was $7.5 million.

In connection with the issuance of the term loan, the Company recorded a debt discount of $13.6 million, inclusive of debt issuance costs, the derivative liability and the relative fair value of the warrants. The discount will be amortized over the life of the term loan using the effective interest method. For the year ended December 31, 2022, the Company recorded $383,000 related to the amortization of the debt discount associated with the Oaktree Agreement.

Prepayments of the term loan, in whole or in part, will be subject to a prepayment fee which declines each year until the fourth anniversary date of the Closing Date, after which no prepayment fee is required. The Company is also required to pay an exit fee upon any payment or prepayment equal to 2.0% of the aggregate principal amount of the loans funded under the Oaktree Agreement. The Company recorded an additional debt discount of $1.0 million related to the exit fee. For the year ended December 31, 2022, the Company recorded $28,000 related to the amortization of the exit fee associated with the Oaktree Agreement.

The Oaktree Agreement contains customary representations, warranties and affirmative and negative covenants, including financial covenants requiring the Company to (i) maintain unrestricted cash of at least $15.0 million at all times, increasing to $20.0 million upon accessing the second tranche of the term loan and (ii) meet minimum quarterly net sales revenue targets.

In addition, the Oaktree Agreement contains customary events of default that could cause the Company’s indebtedness to become immediately due and payable. The lenders could declare the Company in default under its debt obligation upon the occurrence of any event that the lenders interpret as having a material adverse effect as defined under the Oaktree Agreement. Upon the occurrence and for the duration of an event of default, an additional interest rate equal to 2.0% per annum could apply to all obligations owed under the Oaktree Agreement. Among other loan covenant requirements, the Oaktree Agreement also requires the Company to provide an audit opinion of its annual financial statements not subject to any "going concern" or like qualification or exception.

SLR Investment Corp. and Silicon Valley Bank Term Loan

In May 2017, the Company entered into a loan and security agreement (the “2017 Loan Agreement”), with SLR Investment Corp. (f/k/a Solar Capital Ltd.) and Silicon Valley Bank, (together, the “Lenders”) for $10.0 million. The 2017 Loan Agreement had a maturity date of May 1, 2021. Debt issuance costs for the 2017 Loan Agreement were to be amortized to interest expense over the remaining term of the 2017 Loan Agreement using the effective-interest method.

In September 2019, the Company replaced the 2017 Loan Agreement with a new $20.0 million term loan with the Lenders (the "2019 Loan Agreement"). The restructured four-year term loan facility allowed for an expansion of the 2017 Loan Agreement. Some of the proceeds from the 2019 Loan Agreement were used to pay off the 2017 Loan Agreement including the final fee of $325,000. The 2019 Loan Agreement extended the term of the credit facility until September 17, 2023. The payoff of the 2017 Loan Agreement was treated as a modification of the debt. Debt issuance costs for the 2019 Loan Agreement, including unamortized issuance costs for the 2017 Loan Agreement, would be amortized to interest expense over the remaining term of the 2019 Loan Agreement using the effective-interest method.

The interest rate under the 2019 Loan Agreement was the higher of (i) LIBOR plus 7.95% or (ii) 10.18% and there was an interest-only period until September 30, 2021. The rate at December 31, 2022 was 10.18%. Pursuant to the 2019 Loan Agreement, the Company provided a first priority security interest in substantially all of the Company’s assets, including intellectual property, subject to certain exceptions.

The Company entered into the Exit Agreement in connection with the 2019 Loan Agreement which provided for an aggregate payment of 4% of the loan commitment, or $800,000, to the Lenders upon the occurrence of an exit event (the "Exit Fee"). The Company concluded that the exit payment obligation met the definition of a derivative that was required to be accounted for as a separate unit of accounting. The Company recorded the issuance-date fair value of the derivative liability of $763,000 as a debt discount and as a derivative liability in the Company’s balance sheet. The derivative liability was re-measured at each balance sheet date and any changes in estimated fair value was recorded as other income (expense). The Company paid the Exit Fee during the year ended December 31, 2020 in conjunction with the Company’s public offering, which was deemed to be an exit event pursuant to the Exit Agreement. Prior to its public offering in 2020, the Company recorded $30,000 in non-cash expense as a fair value adjustment to the derivative liability.

The 2019 Loan Agreement allowed the Company to voluntarily prepay all (but not less than all) of the outstanding principal at any time. A prepayment premium of 3% or 1% through the one-year anniversary and the two-year anniversary, respectively, would be assessed on the outstanding principal. After the two-year anniversary, a 0.5% prepayment premium would be assessed on the outstanding principal. A final payment fee of $500,000 was due upon the earlier to occur of the maturity date or prepayment of such borrowings.

In connection with the Oaktree Agreement, the Company paid off all unpaid borrowings under the 2019 Loan Agreement on October 13, 2022, including the $500,000 final fee and a prepayment premium of $46,000. For the years ended December 31, 2021, and 2022, the Company recorded $392,000 and $341,000, respectively, related to the amortization of the debt discount associated with the 2019 Loan Agreement. For the years ended December 31, 2021, and 2022, the Company recorded $162,000 and $132,000 related to the amortization of the final payment fee associated with the 2019 Loan Agreement.

As of December 31, 2022, future principal payments due under the Oaktree Agreement are as follows (in thousands):


Year ended:
December 31, 2023	$	-
December 31, 2024		-
December 31, 2025		2,500
December 31, 2026		10,000
December 31, 2027		37,500
Total minimum principal payments	$	50,000

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-URI https://asc.fasb.org/topic&trid=2208564

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
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-URI https://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(c))
-URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 470
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-Paragraph 1I
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
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-Subparagraph (i)
-URI https://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

+ Details

Income Taxes

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Income Taxes

8. Income Taxes

The Company accounts for income taxes in accordance with ASC 740, which requires an asset and liability approach for measuring deferred taxes based on temporary differences between the financial statement and tax bases of assets and liabilities existing at each balance sheet date using enacted tax rates for the years in which taxes are expected to be paid or recovered. The tax benefit arising from the Company’s net loss has been offset by an increase in the valuation allowance.

Accordingly, the Company had no net income tax provision or benefit during the years ended December 31, 2021 and 2022. Components of the net deferred tax assets at December 31, 2021 and 2022 are as follows (in thousands):


	2021			2022
Deferred tax assets:
Federal net operating loss carryforwards	$	12,813		$	17,252
State net operating loss carryforwards		3,630			4,585
Research and development tax credits		3,719			4,214
Accrued liabilities		327			677
Stock-based compensation		1,087			1,329
Depreciation and amortization		247			324
Capitalized research and development costs		29,529			30,976
Lease liabilities		129			146
Other		29			—
Total deferred tax assets		51,510			59,503
Deferred tax liabilities:
Right-of-use lease assets		(111	)		(144	)
Other		—			(273	)
Total deferred tax liabilities	$	(111	)	$	(417	)
Valuation allowance	$	(51,399	)	$	(59,086	)
Net deferred tax assets	$	—		$	—

At December 31, 2022, the Company had available federal net operating loss carryforwards of $17.5 million, which expire at various dates through 2037, and $64.6 million, which may be carried forward indefinitely. At December 31, 2022, the Company had available state net operating loss carryforwards of $72.6 million, which expire at various dates through 2042, and $300,000, which may be carried forward indefinitely. In assessing the realizability of net deferred tax assets, management considers whether it is more likely than not that the net deferred tax assets will be realized. The ultimate realization of net deferred tax assets is dependent upon the generation of future taxable income during the periods in which temporary differences representing future deductible amounts become deductible. Management has established a full valuation allowance against the net deferred tax assets at December 31, 2021 and 2022 since it is more likely than not that these future tax benefits will not be realized. During 2022, the valuation allowance increased by $7.7 million.

At December 31, 2022, the Company had federal and state research and development credit carryforwards of $4.3 million and $1.0 million, respectively. The net credit carryforwards may be used to offset future income taxes and expire at various dates through 2042. Changes in the Company’s ownership, as defined in the U.S. Internal Revenue Code, may limit the Company’s ability to utilize the tax credit and net operating loss carryforwards.

A reconciliation of income tax (expense) benefit at the statutory federal income tax rate and income taxes as reflected in the consolidated financial statements at December 31, 2021 and 2022 are as follows:


	2021			2022
Federal income tax at statutory rate		21.00	%		21.00	%
State income tax, net of federal benefit		5.97	%		4.28	%
Research and development credits		3.16	%		1.39	%
Book compensation related to stock options		0.03	%		(0.80	)%
Change in income tax rate		0.45	%		(4.93	)%
Other		(0.93	)%		(0.09	)%
Increase in valuation allowance		(29.68	)%		(20.87	)%
Effective tax rate		—	%		(0.02	)%

The Company files tax returns in the United States, Massachusetts and other states. The tax years 2018 through 2022 remain open to examination by major taxing jurisdictions to which the Company is subject, which are primarily the United States federal and Massachusetts. Carryforward attributes generated in years past may still be adjusted upon examination by the Internal Revenue Service or state tax authorities if they have or will be used in a future period. The Company is currently not under examination by the Internal Revenue Service or any other jurisdictions for any tax years. The Company recognizes both accrued interest and penalties related to unrecognized benefits in income tax expense. The Company has not recorded any interest or penalties on any unrecognized tax benefits since its inception.

A reconciliation of the beginning and ending amount of uncertain tax benefits is as follows (in thousands):


	2021		2022
Beginning uncertain tax benefits	$	774	$	977
Prior year - increases		—		—
Current year - decreases		—		—
Current year - increases		203		129
Ending uncertain tax benefits	$	977	$	1,106

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 21
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32857-109319

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-URI https://asc.fasb.org/extlink&oid=122134291&loc=d3e330215-122817

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 17
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32809-109319

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-URI https://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32705-109319

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-URI https://asc.fasb.org/extlink&oid=6424409&loc=d3e44925-109338

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-URI https://asc.fasb.org/topic&trid=2144680

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Inventory (Tables)

12 Months Ended

Dec. 31, 2022

Inventory Disclosure [Abstract]

Schedule of Inventory

The Company's inventory balance consists of the following (in thousands):


	As of December 31,
	2021		2022
Raw materials	$	—	$	1,201
Work-in-process		—		29
Finished goods		—		—
	$	—	$	1,230

Debt (Tables)

12 Months Ended

Dec. 31, 2022

Debt Disclosure [Abstract]

Schedule of Carrying Value of Debt Balnce

The following table presents the carrying value of the Company's debt balance as of December 31, 2021 and 2022 (in thousands):


	DECEMBER 31, 2021			DECEMBER 31, 2022
Face value of term loans	$	17,500		$	50,000
Unamortized debt discount		(341	)		(13,206	)
Total debt, net	$	17,159		$	36,794
Less: short-term debt		(9,805	)		—
Long-term debt	$	7,354		$	36,794

Schedule of Future Principal Payments Due

As of December 31, 2022, future principal payments due under the Oaktree Agreement are as follows (in thousands):


Year ended:
December 31, 2023	$	-
December 31, 2024		-
December 31, 2025		2,500
December 31, 2026		10,000
December 31, 2027		37,500
Total minimum principal payments	$	50,000

Description of Business and Basis of Presentation - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Description Of Business And Basis Of Presentation [Line Items]
Cash, cash equivalents, restricted cash and investments		$ 118,400
Working capital		115,900
Net loss		36,838	$ 28,034
Net cash flows used in operating activities		34,577	$ 27,151
Common Stock \| Maximum \| Cowen
Description Of Business And Basis Of Presentation [Line Items]
Aggregate offering price		$ 48,900
Follow On Offering \| Common Stock
Description Of Business And Basis Of Presentation [Line Items]
Proceeds from sale of shares, Net	$ 46,600

Property and Equipment

12 Months Ended

Dec. 31, 2022

Property, Plant and Equipment [Abstract]

Property and Equipment

6. Property and Equipment

Purchased property and equipment consist of the following as of December 31, 2021 and 2022 (in thousands):


	ESTIMATED USEFUL LIFE	2021			2022
Office equipment	5 years	$	10		$	6
Office furniture	7 years		126			126
Computer equipment	3 years		8			15
Leasehold improvements	Life of lease		95			95
			239			242
Less: Accumulated depreciation			(170	)		(188	)
Property and equipment, net		$	69		$	54

Depreciation expense for the years ended December 31, 2021 and 2022 was $34,000 and $37,000, respectively.

Net Loss per Share - Schedule of Antidilutive Securities Excluded from Computation of Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	4,524,522	2,705,002
Stock Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	4,008,177	2,662,752
Warrants to purchase common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	516,345
Unvested Restricted Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share		42,250

Stock-Based Compensation - Schedule of Estimated Fair Value of Options Valuation Assumptions (Details) - $ / shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	1.67%	0.50%
Risk-free interest rate, maximum	4.18%	1.25%
Expected dividend yield	0.00%	0.00%
Expected volatility, minimum	70.00%	72.00%
Expected volatility, maximum	84.00%	74.00%
Weighted-average grant date fair value	$ 3.18	$ 4.18
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	5 years 6 months	5 years 6 months
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	6 years 8 months 12 days	6 years 8 months 12 days

Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2022

Accounting Policies [Abstract]

Use of Estimates

Foreign Currency Transactions

Cash Cash Equivalents and Restricted Cash

Cash, Cash Equivalents and Restricted Cash


	December 31, 2021		December 31, 2022
Cash and cash equivalents	$	74,268	$	71,061
Restricted cash		182		182
Cash, cash equivalents and restricted cash	$	74,450	$	71,243

Concentration of Credit Risk

Investments

Inventory

Prior to FDA approval of FUROSCIX, the Company expensed all inventory-related costs, including that used for clinical development, to research and development ("R&D") costs in the period incurred.

Leases

Debt Issuance Costs

Research and Development Costs

Income Taxes

Stock-Based Compensation

Segments

Recently Issued Accounting Standards

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Taxes [Line Items]
Net income tax provision or benefit	$ 0	$ 0
Federal net operating loss carryforwards expiration year	2037
State net operating loss carryforwards expiration year	2042
Increase in valuation allowance	$ 7,700,000
Research and development credit carryforwards	$ 4,214,000	$ 3,719,000
Federal and state research and development credit carryforwards expiration year	2042
Federal
Income Taxes [Line Items]
Net operating loss carryforwards	$ 64,600,000
Research and development credit carryforwards	4,300,000
Federal \| 2037
Income Taxes [Line Items]
Net operating loss carryforwards	17,500,000
State
Income Taxes [Line Items]
Net operating loss carryforwards	300,000
Research and development credit carryforwards	1,000,000.0
State \| 2041
Income Taxes [Line Items]
Net operating loss carryforwards	$ 72,600,000

Stock-Based Compensation - Summary of Information about Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
NUMBER OF SHARES
Number of shares outstanding, beginning balance	2,662,752	2,224,913
Number of shares granted	1,455,594	953,506
Number of shares exercised	(11,756)	(2,501)
Number of shares forfeited	(98,413)	(513,166)
Number of shares outstanding, ending balance	4,008,177	2,662,752
Vested and exercisable, ending balance	1,982,329
Vested and expected to vest, ending balance	3,489,134
WEIGHTED-AVERAGE EXERCISE PRICE
Weighted average exercise prices, outstanding beginning balance	$ 6.28	$ 6.26
Weighted average exercise prices, granted	4.86	6.57
Weighted average exercise prices, exercised	3.71	3.81
Weighted average exercise prices, forfeited	6.73	6.72
Weighted average exercise prices, outstanding ending balance	5.76	$ 6.28
Weighted average exercise prices, vested and exercisable ending balance	6.15
Weighted average exercise prices, vested and expected to vest ending balance	$ 5.81
WEIGHTED-AVERAGE REMAINING CONTRACTUAL TERM
Weighted average remaining contractual term, outstanding	7 years 5 months 19 days
Weighted average remaining contractual term, vested and exercisable	6 years 3 days
Weighted average remaining contractual term, vested and expected to vest	7 years 3 months
AGGREGATE INTRINSIC VALUE
Aggregate intrinsic value, outstanding ending balance	$ 7,147
Aggregate intrinsic value, vested and exercisable ending balance	3,436
Aggregate intrinsic value, vested and expected to vest ending balance	$ 6,226

Commitments and Contingencies - Schedule of Lease Cost and Other Information of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Lease cost:
Operating lease cost	$ 505	$ 482
Short-term lease cost	37	20
Sublease income	(47)	(51)
Total lease cost	495	451
Other information
Cash paid for amounts included in the measurement of liabilities	551	530
Operating cash flows from operating leases	$ (57)	$ (60)
Weighted-average remaining lease term - operating leases	10 months 24 days	10 months 24 days
Weighted-average discount rate - operating leases	10.10%	10.10%

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Schedule of Estimated Fair Value of Options Valuation Assumptions

The fair value of options at date of grant was estimated using the Black-Scholes option-pricing model with the following assumptions:


	2021		2022
Risk-free interest rate	0.50%—1.25%		1.67%—4.18%
Expected dividend yield	0%		0%
Expected life	5.5—6.7 years		5.5—6.7 years
Expected volatility	72%—74%		70%—84%
Weighted-average grant date fair value	$	4.18	$	3.18

Summary of Information about Stock Option Activity

The following table summarizes information about stock option activity during 2021 and 2022 (in thousands, except share and per share data):


	NUMBER OF SHARES			WEIGHTED- AVERAGE EXERCISE PRICE		WEIGHTED- AVERAGE REMAINING CONTRACTUAL TERM		AGGREGATE INTRINSIC VALUE
Outstanding, December 31, 2020		2,224,913		$	6.26
Granted		953,506			6.57
Exercised		(2,501	)		3.81
Forfeited		(513,166	)		6.72
Outstanding, December 31, 2021		2,662,752		$	6.28
Granted		1,455,594			4.86
Exercised		(11,756	)		3.71
Forfeited		(98,413	)		6.73
Outstanding, December 31, 2022		4,008,177		$	5.76		7.47	$	7,147
Vested and exercisable, December 31, 2022		1,982,329		$	6.15		6.01	$	3,436
Vested and expected to vest, December 31, 2022		3,489,134		$	5.81		7.25	$	6,226

Schedule of RSU Activity

The following table summarizes information about RSU activity during 2021 and 2022:


	RSUs			AVERAGE GRANT DATE FAIR VALUE (IN DOLLARS PER SHARE)
RSUs outstanding, December 31, 2020		80,450		$	3.25
Granted		—			—
Vested		(38,200	)		3.25
Forfeited		—			—
RSUs outstanding, December 31, 2021		42,250			3.25
Granted		—			—
Vested		(42,250	)		3.25
Forfeited		—			—
RSUs outstanding, December 31, 2022		—		$	—

Summary of Stock-Based Compensation Expense

The Company recorded stock-based compensation expense in the following expense categories of its accompanying condensed consolidated statements of operations and comprehensive loss for employees, directors and non-employees during the years ended December 31, 2021 and 2022 as follows (in thousands):


	2021		2022
Research and development	$	947	$	1,050
General and administrative		1,419		1,788
Total	$	2,366	$	2,838

Inventory

12 Months Ended

Dec. 31, 2022

Inventory Disclosure [Abstract]

Inventory

5. Inventory

The Company's inventory balance consists of the following (in thousands):


	As of December 31,
	2021		2022
Raw materials	$	—	$	1,201
Work-in-process		—		29
Finished goods		—		—
	$	—	$	1,230

Inventory is stated at the lower of cost and net realizable value and consists of raw materials, work-in-process and
finished goods. The Company began capitalizing inventory costs following FDA approval of FUROSCIX in October 2022 and has not recorded any significant inventory write-downs since that time. The Company currently uses a limited number of third-party contract manufacturing organizations ("CMOs") to produce its inventory.

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2022

Accrued Liabilities, Current [Abstract]

Schedule of Accrued Expenses

Accrued expenses at December 31, 2021 and 2022 consist of (in thousands):


	2021		2022
Employee compensation and related costs	$	1,152	$	2,754
Contract research and development		2,350		1,827
Consulting and professional service fees		265		603
State taxes		5		49
Financing related costs		60		29
Interest		154		16
Other		9		11
Total accrued expenses	$	3,995	$	5,289

Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2022

Fair Value Disclosures [Abstract]

Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis


	As of December 31, 2021
	TOTAL		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	$	72,449	$	72,449	$	—	$	—
Total cash equivalents		72,449		72,449		—		—

Corporate debt securities		1,010		—		1,010		—
Investments		1,010		—		1,010		—

Total	$	73,459	$	72,449	$	1,010	$	—


	As of December 31, 2022
	TOTAL		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	$	65,875	$	65,875	$	—	$	—
Total cash equivalents		65,875		65,875		—		—

Commercial Paper		16,741		—		16,741		—
United States Treasury securities		15,775		15,775		—		—
United States Government Agency securities		14,609		—		14,609		—
Investments		47,125		15,775		31,350		—

Total	$	113,000	$	81,650	$	31,350	$	—
Liabilities:
Derivative liability	$	7,517	$	—	$	—	$	7,517

Total	$	7,517	$	—	$	—	$	7,517

Schedule of Changes in Fair Value of Level 3 Derivative Liability

Changes in the fair value of the Company’s Level 3 derivative liability for the year ended December 31, 2022 are as follows:


At December 31, 2021	$	—
Initial fair value of derivative liability		8,852
Change in fair value of derivative liability		(1,335	)
At December 31, 2022	$	7,517

Schedule of Quantitative Information about Significant Unobservable Inputs


	October 13, 2022	December 31, 2022
Net sales discount rate	23.3%	22.3%
Net sales volatility	80.0%	80.0%
Risk-free rate	4.2%	4.0%
Recovery rate	80.0%	80.0%

Stock-Based Compensation

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

12. Stock-Based Compensation

Stock Options

In October 2017, the board of directors approved the 2017 Stock Option and Incentive Plan (the “2017 Stock Plan”) which became effective in November 2017, upon the closing of the Company’s IPO. The 2017 Stock Plan will expire in October 2027. Under the 2017 Stock Plan, the Company may grant incentive stock options, non-statutory stock options, restricted stock awards, RSUs and other stock-based awards. The Company’s 2014 Stock Incentive Plan (the “2014 Stock Plan”) terminated in November 2017 effective upon the completion of the Company’s IPO. No additional options will be granted under the 2014 Stock Plan. At December 31, 2022, there were 598,411 options outstanding under the 2014 Stock Plan.

At December 31, 2022, there were 6,105,147 shares of the Company’s common stock authorized for issuance under the 2017 Stock Plan, including 359,860 options that have been forfeited from the 2014 Stock Plan.

At December 31, 2022, there were 2,655,289 options available for issuance and 3,409,766 options outstanding under the 2017 Stock Plan. Awards granted under the 2017 Stock Plan have a term of ten years. Vesting of awards under the 2017 Stock Plan is determined by the compensation committee of the board of directors but is generally over one to four-year terms.

The fair value of options at date of grant was estimated using the Black-Scholes option-pricing model with the following assumptions:


	2021		2022
Risk-free interest rate	0.50%—1.25%		1.67%—4.18%
Expected dividend yield	0%		0%
Expected life	5.5—6.7 years		5.5—6.7 years
Expected volatility	72%—74%		70%—84%
Weighted-average grant date fair value	$	4.18	$	3.18

Due to the lack of a public market for the trading of the Company’s common stock prior to its initial public offering and the lack of company-specific historical volatility, volatility was estimated using historical volatilities of similar companies. The expected life of the awards is estimated based on the simplified method, which calculates the expected life based upon the midpoint of the term of the award and the vesting period. The Company uses the simplified method because it does not have sufficient option exercise data to provide a reasonable basis upon which to estimate the expected term. The Company has no history of paying dividends nor does management expect to pay dividends over the contractual terms of these options. The risk-free interest rates are based on the United States Treasury yield curve in effect at the time of grant, with maturities approximating the expected life of the stock options.

The following table summarizes information about stock option activity during 2021 and 2022 (in thousands, except share and per share data):


	NUMBER OF SHARES			WEIGHTED- AVERAGE EXERCISE PRICE		WEIGHTED- AVERAGE REMAINING CONTRACTUAL TERM		AGGREGATE INTRINSIC VALUE
Outstanding, December 31, 2020		2,224,913		$	6.26
Granted		953,506			6.57
Exercised		(2,501	)		3.81
Forfeited		(513,166	)		6.72
Outstanding, December 31, 2021		2,662,752		$	6.28
Granted		1,455,594			4.86
Exercised		(11,756	)		3.71
Forfeited		(98,413	)		6.73
Outstanding, December 31, 2022		4,008,177		$	5.76		7.47	$	7,147
Vested and exercisable, December 31, 2022		1,982,329		$	6.15		6.01	$	3,436
Vested and expected to vest, December 31, 2022		3,489,134		$	5.81		7.25	$	6,226

The following table summarizes information about RSU activity during 2021 and 2022:


	RSUs			AVERAGE GRANT DATE FAIR VALUE (IN DOLLARS PER SHARE)
RSUs outstanding, December 31, 2020		80,450		$	3.25
Granted		—			—
Vested		(38,200	)		3.25
Forfeited		—			—
RSUs outstanding, December 31, 2021		42,250			3.25
Granted		—			—
Vested		(42,250	)		3.25
Forfeited		—			—
RSUs outstanding, December 31, 2022		—		$	—

The number of RSUs vested includes shares of common stock withheld on behalf of employees to satisfy the minimum statutory tax withholding requirements.

During 2021 and 2022, the Company received $9,000 and $44,000, respectively, upon exercise of stock options. The intrinsic value of the options exercised in 2021 and 2022 was $7,000 and $18,000, respectively.

Unrecognized compensation expense related to unvested options as of December 31, 2022 was $4.2 million and will be recognized over the remaining vesting periods of the underlying awards. The weighted-average period over which such compensation is expected to be recognized is 2.5 years.

Employee Stock Purchase Plan

In October 2017, the board of directors approved the 2017 Employee Stock Purchase Plan (“the ESPP”) which became effective in November 2017, upon the closing of the Company’s IPO. As part of the ESPP, eligible employees may acquire an ownership interest in the Company by purchasing common stock, at a discount, through payroll deductions. Eligible employees who elected to participate were able to participate in the ESPP beginning September 1, 2021.

During 2021 and 2022, 11,253 and 45,938 shares of common stock were issued under the ESPP, respectively. As of December 31, 2022, there were 1,142,691 shares of common stock available for issuance under the ESPP.


	2021		2022
Research and development	$	947	$	1,050
General and administrative		1,419		1,788
Total	$	2,366	$	2,838

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Schedule of Components of Net Deferred Tax Assets

Components of the net deferred tax assets at December 31, 2021 and 2022 are as follows (in thousands):


	2021			2022
Deferred tax assets:
Federal net operating loss carryforwards	$	12,813		$	17,252
State net operating loss carryforwards		3,630			4,585
Research and development tax credits		3,719			4,214
Accrued liabilities		327			677
Stock-based compensation		1,087			1,329
Depreciation and amortization		247			324
Capitalized research and development costs		29,529			30,976
Lease liabilities		129			146
Other		29			—
Total deferred tax assets		51,510			59,503
Deferred tax liabilities:
Right-of-use lease assets		(111	)		(144	)
Other		—			(273	)
Total deferred tax liabilities	$	(111	)	$	(417	)
Valuation allowance	$	(51,399	)	$	(59,086	)
Net deferred tax assets	$	—		$	—

Schedule of Reconciliation of Income Tax (Expense) Benefit


	2021			2022
Federal income tax at statutory rate		21.00	%		21.00	%
State income tax, net of federal benefit		5.97	%		4.28	%
Research and development credits		3.16	%		1.39	%
Book compensation related to stock options		0.03	%		(0.80	)%
Change in income tax rate		0.45	%		(4.93	)%
Other		(0.93	)%		(0.09	)%
Increase in valuation allowance		(29.68	)%		(20.87	)%
Effective tax rate		—	%		(0.02	)%

Schedule of Reconciliation of Uncertain Tax Benefits

A reconciliation of the beginning and ending amount of uncertain tax benefits is as follows (in thousands):


	2021		2022
Beginning uncertain tax benefits	$	774	$	977
Prior year - increases		—		—
Current year - decreases		—		—
Current year - increases		203		129
Ending uncertain tax benefits	$	977	$	1,106

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	At The Market Offering	Common Stock	Common Stock At The Market Offering	Additional Paid-in Capital	Additional Paid-in Capital At The Market Offering	Accumulated Deficit	Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2020	$ 82,170		$ 3		$ 243,830		$ (161,664)	$ 1
Beginning Balance, Shares at Dec. 31, 2020			27,325,959
Net loss	(28,034)						(28,034)
Issuance of common stock upon exercise of stock options	$ 9				9
Issuance of common stock upon exercise of stock options, Shares	2,501		2,501
Issuance of common stock purchased through employee stock purchase plan	$ 42				42
Issuance of common stock purchased through employee stock purchase plan, Shares			11,253
Vesting of restricted stock	(81)				(81)
Vesting of restricted stock, Shares			26,994
Stock-based compensation	2,366				2,366
Unrealized gain (loss) on short term investments	(2)							(2)
Ending Balance at Dec. 31, 2021	56,470		$ 3		246,166		(189,698)	(1)
Ending Balance, Shares at Dec. 31, 2021			27,366,707
Net loss	(36,838)						(36,838)
Issuance of common stock, net of issuance costs		$ 1,114				$ 1,114
Issuance of common stock net of issuance costs, Shares				181,553
Issuance of common stock and pre-funded warrants in common stock offering, net of issuance costs	46,645				46,645
Issuance of common stock and pre-funded warrants in common stock offering, net of issuance costs, Shares			6,620,000
Issuance of common stock upon exercise of stock options	$ 44				44
Issuance of common stock upon exercise of stock options, Shares	11,756		11,756
Issuance of common stock purchased through employee stock purchase plan	$ 173				173
Issuance of common stock purchased through employee stock purchase plan, Shares			45,938
Vesting of restricted stock	(54)				(54)
Vesting of restricted stock, Shares			31,962
Issuance of warrants	2,008				2,008
Stock-based compensation	2,838				2,838
Unrealized gain (loss) on short term investments	33							33
Ending Balance at Dec. 31, 2022	$ 72,433		$ 3		$ 298,934		$ (226,536)	$ 32
Ending Balance, Shares at Dec. 31, 2022			34,257,916

Commitments and Contingencies - Schedule of Maturity Analysis of Annual Undiscounted Cash Flows of Operating Lease Liabilities (Details) $ in Thousands	Dec. 31, 2022 USD ($)
Year ended:
December 31, 2023	$ 596
December 31, 2024	9
December 31, 2025	1
Total minimum lease payments	606
Less imputed interest	(32)
Total	$ 574

Income Taxes - Schedule of Reconciliation of Uncertain Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Beginning uncertain tax benefits	$ 977	$ 774
Prior year - increases	0	0
Current year - decreases	0	0
Current year - increases	129	203
Ending uncertain tax benefits	$ 1,106	$ 977

Investments - Summary of Amortized Cost and Fair Value of Available-for-Sale Investments by Contract Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Amortized Cost, Due in one year or less	$ 47,093
Amortized Cost, Total	47,093	$ 1,011
Fair value, Due in one year or less	47,125
Fair Value, Total	$ 47,125	$ 1,010

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2022

Commitments and Contingencies Disclosure [Abstract]

Schedule of Maturity Analysis of Annual Undiscounted Cash Flows of Operating Lease Liabilities

The following is a maturity analysis of the annual undiscounted cash flows reconciled to the carrying value of the operating lease liabilities as of December 31, 2022 (in thousands):


Year ended:
December 31, 2023	$	596
December 31, 2024		9
December 31, 2025		1
Total minimum lease payments		606
Less imputed interest		(32	)
Total	$	574

Schedule of Lease Cost and Other Information of Operating Lease Liabilities


	2021			2022
Lease cost:
Operating lease cost	$	482		$	505
Short-term lease cost		20			37
Sublease income		(51	)		(47	)
Total lease cost	$	451		$	495
Other information
Cash paid for amounts included in the measurement of liabilities	$	530		$	551
Operating cash flows from operating leases	$	(60	)	$	(57	)
Weighted-average remaining lease term - operating leases	0.9 years			0.9 years
Weighted-average discount rate - operating leases		10.1	%		10.1	%

Investments (Tables)

12 Months Ended

Dec. 31, 2022

Investments, Debt and Equity Securities [Abstract]

Summary of Available-for-Sale Classified Investments

A summary of the Company’s available-for-sale classified investments as of December 31, 2021 and 2022 consisted of the following (in thousands):


	At December 31, 2021
Investments - Current:	Cost Basis		Accumulated Unrealized Gains		Accumulated Unrealized Losses			Fair Value
Corporate debt securities	$	1,011	$	-	$	(1	)	$	1,010
Total	$	1,011	$	-	$	(1	)	$	1,010


	At December 31, 2022
Investments - Current:	Cost Basis		Accumulated Unrealized Gains		Accumulated Unrealized Losses		Fair Value
Commercial paper	$	16,741	$	-	$	-	$	16,741
United States Treasury securities		15,768		7		-		15,775
United States Government Agency securities		14,584		25		-		14,609
Total	$	47,093	$	32	$	-	$	47,125

Summary of Amortized Cost and Fair Value of Available-for-Sale Investments by Contract Maturity

The amortized cost and fair value of the Company’s available-for-sale investments, by contract maturity, as of December 31, 2022 consisted of the following (in thousands):


	Amortized Cost		Fair Value
Due in one year or less	$	47,093	$	47,125
Total	$	47,093	$	47,125

Income Taxes - Schedule of Reconciliation of Income Tax (Expense) Benefit (Details)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Federal income tax at statutory rate	21.00%	21.00%
State income tax, net of federal benefit	4.28%	5.97%
Research and development credits	1.39%	3.16%
Book compensation related to stock options	(0.80%)	0.03%
Change in income tax rate	(4.93%)	0.45%
Other	(0.09%)	(0.93%)
Increase in valuation allowance	(20.87%)	(29.68%)
Effective tax rate	(0.02%)	0.00%

Stock-Based Compensation - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional options granted	1,455,594	953,506
Stock option, number of shares outstanding	4,008,177	2,662,752	2,224,913
Cash received upon exercise of stock options	$ 44,000	$ 9,000
Intrinsic value of options exercised	18,000	$ 7,000
Unrecognized compensation expense	$ 4,200,000
Recognition period (in years)	2 years 6 months
2017 Stock Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option and incentive plan effective date	Nov. 30, 2017
Stock option and incentive plan expiration date	Oct. 31, 2027
Stock option, number of shares outstanding	3,409,766
Number of common stock initially reserved for issuance	6,105,147
Stock options, available for issuance	2,655,289
Term of option granted	10 years
2017 Stock Plan \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option vesting term	1 year
2017 Stock Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option vesting term	4 years
2014 Stock Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option and incentive plan expiration date	Nov. 30, 2017
Additional options granted	0
Stock option, number of shares outstanding	598,411
Number of options forfeited	359,860
2017 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common stock shares issued	45,938	11,253
Number of common stock shares available for issuance	1,142,691

Debt - Schedule of Carrying Value of Debt Balance (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Debt Disclosure [Abstract]
Face value of term loans	$ 50,000	$ 17,500
Unamortized debt discount	(13,206)	(341)
Total debt, net	36,794	17,159
Less: short-term debt		(9,805)
Long-term debt	$ 36,794	$ 7,354

- Definition

Amount, excluding unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

+ References + Details

Property and Equipment - Schedule of Purchased Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 242	$ 239
Less: Accumulated depreciation	(188)	(170)
Property and equipment, net	$ 54	69
Office Equipment
Property Plant And Equipment [Line Items]
ESTIMATED USEFUL LIFE	5 years
Property and equipment, gross	$ 6	10
Office Furniture
Property Plant And Equipment [Line Items]
ESTIMATED USEFUL LIFE	7 years
Property and equipment, gross	$ 126	126
Computer Equipment
Property Plant And Equipment [Line Items]
ESTIMATED USEFUL LIFE	3 years
Property and equipment, gross	$ 15	8
Leasehold Improvements
Property Plant And Equipment [Line Items]
ESTIMATED USEFUL LIFE	Life of lease
Property and equipment, gross	$ 95	$ 95

Inventory - Schedule of Inventory (Details) $ in Thousands	Dec. 31, 2022 USD ($)
Inventory Disclosure [Abstract]
Raw materials	$ 1,201
Work-in-process	29
Inventory, Net, Total	$ 1,230