	December 31, 2021
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. corporate debt	$	15,009	$	—	$	(3	)	$	15,006
Foreign corporate debt		10,551		—		(3	)		10,548
U.S. commercial paper		5,998		—		—			5,998
Foreign commercial paper		35,487		—		—			35,487
Total	$	67,045	$	—	$	(6	)	$	67,039

	December 31, 2020
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
U.S. treasury bills and government agency obligations	$	20,110	$	166	$	—	$	20,276
U.S. corporate debt securities		11,505		42		—		11,547
Foreign corporate debt securities		15,508		49		—		15,557
U.S. commercial paper		13,997		—		—		13,997
Foreign commercial paper		41,976		—		—		41,976
Total	$	103,096	$	257	$	—	$	103,353

The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. We regularly monitor and evaluate the realizable value of our marketable securities. We did not recognize any impairment losses for the years ended December 31, 2021 and 2020.

Unrealized gains and losses associated with our investments are reported in accumulated other comprehensive loss. For the year ended December 31, 2021, we recorded $0.3 million in net unrealized losses associated with our short-term investments. For both years ended December 31, 2020 and 2019, we recorded $0.2 million in net unrealized gains associated with our short-term investments.

Realized gains and losses associated with our investments, if any, are reported in the statements of operations and comprehensive loss. We did not recognize any realized gains or losses during the years ended December 31, 2021 and 2020. We recognized $8,000 in realized gains during the year ended December 31, 2019.

	December 31,
	2021		2020
Raw materials	$	21,193	$	18,994
Work in process		20,935		6,847
Finished goods		6,254		16,064
Total inventory	$	48,382	$	41,905

As of December 31, 2021, total inventory included $23.6 million related to ZYNRELEF, $23.1 million related to CINVANTI, and $1.7 million related to SUSTOL. As of December 31, 2020, total inventory included $37.8 million related to CINVANTI and $4.1 million related to SUSTOL. In addition, cost of product sales for the years ended December 31, 2021 and 2020 included charges of $3.8 million and $0.1 million, respectively, resulting from the write-off of short-dated SUSTOL inventory.

	December 31,
	2021		2020
Prepaid expenses	$	28,048	$	19,461
Prepaid insurance		2,135		2,155
Deposits		254		346
Interest receivable		245		334
Total prepaid expenses and other assets	$	30,682	$	22,296

	December 31,
	2021			2020
Scientific equipment	$	33,403		$	29,135
Leasehold improvements		610			878
Computer equipment and software		1,497			1,461
Furniture, fixtures and office equipment		1,467			2,135
Property and equipment, gross		36,977			33,609
Less: accumulated depreciation and amortization		(13,243	)		(10,872	)
Property and equipment, net	$	23,734		$	22,737

Depreciation and amortization expense for the years ended December 31, 2021, 2020 and 2019 was $3.0 million, $2.8 million and $2.0 million, respectively. As of December 31, 2021 and 2020, $15.9 million and $14.1 million of property and equipment, respectively, was in process and not depreciated during the respective years.

Accrued payroll and employee liabilities consist of the following (in thousands):

	December 31,
	2021		2020
Accrued employee salaries and benefits	$	1,784	$	1,691
Accrued bonuses		9,439		8,479
Accrued vacation		4,040		3,427
Total accrued payroll and employee liabilities	$	15,263	$	13,597

	December 31,
	2021		2020
Accrued product sales allowances	$	22,560	$	24,571
Accrued consulting and professional fees		2,666		3,450
Accrued accounts payable		70		104
Other accrued liabilities		563		244
Total other accrued liabilities	$	25,859	$	28,369