Stock-Based Compensation

3 Months Ended

Mar. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

8.  Stock-Based Compensation

In January 2020, the number of shares available for issuance under the Tetraphase Pharmaceuticals, Inc. 2013 Stock Incentive Plan, as amended, or 2013 Plan, was increased by approximately 0.1 million shares as a result of the automatic increase provision of the 2013 Plan. As of March 31, 2020, the total number of shares of common stock available for issuance under the 2013 Plan was approximately 0.4 million.

Stock-Based Compensation Expense

During the three months ended March 31, 2020 and 2019, the Company recognized the following stock-based compensation expense (in thousands):

	Three Months Ended
	March 31,
	2020		2019
Research and development	$	106	$	983
General and administrative		374		1,740
Total	$	480	$	2,723
	Three Months Ended
	March 31,
	2020		2019
Stock options	$	366	$	1,977
Restricted stock units		114		726
Employee stock purchase plan		-		20
Total	$	480	$	2,723

Stock Options

The following table summarizes the stock option activity for the three months ended March 31, 2020:

	Shares			Weighted- Average Exercise Price
Outstanding at December 31, 2019		177,768		$	223.53
Canceled		(29,514	)	$	265.42
Outstanding at March 31, 2020		148,254		$	215.20
Exercisable at March 31, 2020		113,255		$	253.33

As of March 31, 2020, there was $2.3 million of total unrecognized stock-based compensation cost related to employee unvested stock options granted under the 2013 Plan. The Company expects to recognize that cost over a remaining weighted-average period of 1.7 years.

Restricted Stock Units and Performance Stock Units

The following table summarizes the restricted stock unit, or RSU, and performance stock unit, or PSU, activity for the three months ended March 31, 2020:

	Shares			Weighted- Average Grant Date Fair Value
Unvested at December 31, 2019		91,981		$	28.62
Canceled		(19,845	)	$	34.56
Vested/Released		(22,363	)	$	27.03
Unvested at March 31, 2020		49,773		$	26.97

As of March 31, 2020, there was total unrecognized stock-based expense of $0.7 million related to RSUs and $44,000 related to PSUs. The expense is expected to be recognized over a weighted-average period of 1.5 years.    

Employee stock purchase plan

On March 15, 2020,  the Company’s 2014 Employee Stock Purchase Plan, as amended, was terminated.