Merck & Co has announced the end of the line for its investigational Parkinson's disease drug preladenant, after the drug failed to show much promise in late-stage trials.

Analysis of data from three separate Phase III studies did not provide any evidence of efficacy for preladenant in the treatment of PD compared with placebo, the firm said, but also stressed that there were no safety issues.

Consequently, Merck is now taking steps to discontinue the extension phases of these studies, and will no longer seek marketing approval for the drug, it said.

The company gained the investigational investigational adenosine A2A receptor antagonist via its $4.1-billion purchase of Schering-Plough in 2009, which had carried out successful Phase II trials.