Shares in the USA’s Acadia Pharmaceuticals have collapsed after the firm and partner Biovail Corp noted that pimavanserin failed to meet its primary endpoint in a late-stage trial of patients with Parkinson's disease psychosis.

The companies noted that pimavanserin did not significantly reduce psychotic episodes compared to placebo in the 298-patient study. It did, however, meet a secondary endpoint of motoric tolerability and was safe and well tolerated.

Acadia chief executive Uli Hacksell said that “while we obviously are disappointed with the results of this Phase III study, we continue to believe in the potential of pimavanserin based on our clinical experience to date”. He added that the San Diego-based company is continuing with a second Phase III PDP trial and pimavanserin, a 5-HT2A receptor inverse agonist, is also being studied as a treatment for Alzheimer’s disease psychosis.

How committed Biovail is committed to further development remains to be seen, seeing as how the Canadian drugmaker’s chief executive Bill Wells said that “we will analyse the data in conjunction with Acadia over the next several weeks before deciding on next steps”. He also expressed his disappointment but added that “such setbacks are not uncommon in the industry and are a reminder that we need to continue to build our pipeline with promising compounds”.

Over 1.5 million people in the USA suffer from Parkinson’s disease and up to 40% of patients may develop psychotic symptoms, notably visual hallucinations and delusions. Currently there is no therapy approved to treat PDP.