Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities
Net loss	$ (5,055)	$ (10,281)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	200	277
Amortization of debt issuance costs and debt discount	43	(128)
Stock-based compensation	493	619
Noncash interest expense and other charges	308	4,705
Provision for doubtful accounts receivable		(6)
Provision for excess and obsolete inventories	46	(79)
Changes in operating assets and liabilities:
Accounts receivable	42	(221)
Inventories	(776)	563
Prepaid expenses and other current assets	(391)	(523)
Other assets		98
Accounts payable	(179)	486
Accrued compensation	(181)	92
Accrued expenses and other current liabilities	(543)	(2,288)
Other long-term liabilities and accrued interest	(3)	(191)
Net cash used in operating activities	(5,996)	(6,877)
Cash flows from investing activities
Purchase of property and equipment	(83)
Proceed from sale of property and equipment	18	46
Net cash provided by (used in) investing activities	(65)	46
Cash flows from financing activities
Proceeds from the issuance of convertible preferred stock, net of issuance costs		15,534
Proceeds from the issuance of common stock related to warrant exercises	6,340
Proceeds from the issuance of common stock under officers and directors purchase plan	18
Proceeds from the issuance of common stock in public offerings, net		326
Net cash provided by financing activities	6,358	15,860
Net change in cash and cash equivalents	297	9,029
Cash and cash equivalents, beginning of period	16,410	5,389
Cash and cash equivalents, end of period	16,707	14,418
Supplemental disclosure of cash flow information
Cash paid for interest
Noncash investing and financing activities:
Conversion of CRG loan principal into Series A Preferred Stock		38,000
Accretion of Series A Preferred Stock dividends	895	410
Issuance of Series A Preferred Stock to pay dividends	2,918
Transfers between inventory and property and equipment	198
Deemed dividend arising from beneficial conversion feature of convertible preferred stock		$ 5,216