Note 6. Stockholders’ Equity

On June 20, 2018, the Company's stockholders approved an amendment to the Company's Restated Certificate of Incorporation, as amended, to effect a reverse stock split of the Company's outstanding shares of common stock at a ratio within a range from 1-for-4 to 1-for-8 and set the number of authorized shares of the Company’s common stock at a number determined by calculating the product of 280,000,000 multiplied by two times (2x) the reverse stock split ratio. As further described in Note 12, in July 2018, the Company effected a 1-for-8 reverse stock split of its common stock and set the number of authorized shares of the Company’s common stock at 70,000,000.

Common Stock Warrants

In connection with various financing transactions, the Company has issued warrants to purchase shares of the Company’s common stock. The Company accounts for warrants as equity instruments, derivative liabilities, or liabilities, depending on the specific terms of the warrant. As of June 30, 2018 and December 31, 2017, all of the Company’s outstanding warrants were equity-classified.

Note 6. Stockholders’ Equity (Continued)

The following table summarizes outstanding warrants to purchase shares of the Company’s common stock as of June 30, 2018 and December 31, 2017:


	Number of Shares
	June 30,	December 31,	Weighted-Average
Description	2018	2017	Exercise Price		Expiration Date
Issued in May 2013 financing	—	2,700,791		$ 3.76	May 2018
Issued in May 2013 financing (pre-funded)	1,977,041	1,977,041		$ 0.08	May 2020
Issued in September 2013 financing (pre-funded)	521,997	521,997		$ 0.08	Sep 2020
Issued in February 2014 financing (pre-funded)	269,844	269,844		$ 0.08	Feb 2021
Total	2,768,882	5,469,673

The table below is a summary of the Company's warrant activity for the six months ended June 30, 2018:


	Number of	Weighted-Average
	Warrants	Exercise Price
Outstanding at December 31, 2017	5,469,673	$	1.90
Issued	—		—
Exercised (1)	(2,700,791)		3.76
Expired	—		—
Outstanding at June 30, 2018	2,768,882	$	0.08

(1) During the six months ended June 30, 2018, a related party exercised certain of these warrants as more fully described in Note 10.