The following is a summary of warrant activity for the three months ended March 31, 2019 and 2018:

 

 

All of the warrant agreements provide for a cashless exercise in the event a registration statement covering the issuance of the shares of common stock underlying the warrants is not effective, whereby the number of warrants to be issued will be reduced by the number of shares which could be purchased from the proceeds of the exercise of the respective warrant. The outstanding warrants expire from 2020 through 2025.