24 May 2013 - 24 May 2013 - US Merck & Co's (NYSE:MRK) said yesterday an initial review of findings from three Phase III studies of its investigational drug, preladenant, intended as a therapy of Parkinson's disease (PD), did not provide proof for its efficacy versus placebo.

Preladenant is an adenosine A2A receptor antagonist.

Following these data, the company will terminate the extension phases of these randomised, controlled trials and will not seek approval of the medicine.

The studies assessed the safety and efficacy of preladenant, specifically in combination with levodopa therapy in patients with moderate-to-severe PD in two of the trials and as a monotherapy in early PD in the remaining one.