Note 9 - Stock-based Compensation

3 Months Ended

Mar. 31, 2023

Notes to Financial Statements

Share-Based Payment Arrangement [Text Block]

Note 9 – Stock-Based Compensation

We recognize expense in our interim unaudited condensed consolidated financial statements related to all stock-based awards granted to employees and non-employee directors based on their fair value on the date of grant. Compensation expense related to stock options is calculated using the Black-Scholes option-pricing model and is recognized ratably over the vesting period, which is typically three years. Compensation expense related to restricted stock unit, or RSU, awards is also recognized ratably over the vesting period, which is typically between one to three years.

A summary of activity under our long-term incentive plans is presented below:

(in thousands, except for weighted-average data)
Stock Options	Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (In Yrs)
Outstanding at January 1, 2023		78		$	381.00
Forfeited or expired		(7	)		319.69
Outstanding at March 31, 2023		71		$	376.68		7.1
Vested and exercisable at March 31, 2023		53		$	456.01		6.6
Vested and expected to vest at March 31, 2023		69		$	377.17		7.1

(in thousands, except for weighted-average data)
Restricted Stock Units	Shares			Weighted- Average Grant Date Fair Value
Outstanding at January 1, 2023		11		$	49.50
Vested		(3	)		51.00
Cancelled		(1	)		48.61
Outstanding at March 31, 2023		7		$	49.31

The table below summarizes the total stock-based compensation expense included in the interim unaudited condensed consolidated statements of operations for the periods presented:

	Three Months Ended March 31,
(in thousands)	2023		2022
Research and development	$	129	$	235
General and administrative		156		535
Total	$	285	$	770

The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing formula that uses assumptions noted in the following table. Expected volatilities are based upon the historical volatility of our common stock and other factors. We also use historical data and other factors to estimate option exercises and forfeiture rates. The risk-free interest rates are based upon the U.S. Treasury yield curve in effect at the time of the grant.

	Three Months Ended March 31,
	2022
Weighted average expected volatility		106%
Weighted average expected term (in years)		6.9
Weighted average risk-free interest rate		1.70%
Expected dividends		-