Note 6 - Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2019

Notes Tables

Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Research and development	$	13,577	$	16,274	$	27,173	$	32,646
General and administrative		135,503		303,495		213,111		611,790
Total stock-based compensation expense	$	149,080	$	319,769	$	240,284	$	644,436

Share-based Payment Arrangement, Option, Activity [Table Text Block]

	Number of Options			Weighted average exercise price per share		Weighted average remaining contractual life (in years)
Balance at January 1, 2019		203,736		$	88.14
Granted		117,270			2.62
Forfeited		(11,583	)		83.81
Expired		(147	)		276.00
Outstanding at June 30, 2019		309,276		$	55.78		7.48
Exercisable at June 30, 2019		187,910		$	87.96		6.17

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	2019			2018
Expected term (in years)		5.57			5.57
Risk-free interest rate		2.2	%		2.4	%
Expected volatility		113.4	%		114.7	%
Dividend yield		—	%		—	%