Pfizer and Medivation part company after Alzheimer's trial failure

Pfizer and Medivation have halted research of Alzheimer's drug candidate Dimebon and agreed to terminate their co-development deal for the drug after it failed in a phase III trial.

Dimebon (latrepirdine) provided no additional benefit when added to treatment with donepezil in the CONCERT study involving patients with mild-to-moderate forms of Alzheimer's disease.

The 1,003-patient trial looked at two doses of Dimebon (5mg or 20mg) given three times a day versus placebo, but at no dose was the drug able to show statistically significant improvements in cognitive ability and measurements of self-care and daily functioning.

This is the second failure for Dimebon in a phase III trial, after data from the CONNECTION trial in 2010 showed that the drug missed its primary endpoints of improvements in cognition, memory and global function.

An earlier study in moderate-to-severe Alzheimer's was terminated due to lack of efficacy, and the drug also failed in the phase III HORIZON trial in Huntington disease patients.

Dimebon is actually an old antihistamine drug, and was developed for Alzheimer's after animal studies suggested it might keep neurons from degenerating, complementing the action of drugs like donepezil which alleviate symptoms but do not interrupt the underlying pathology of the disease.

The drug follows late-stage failures for several other disease-modifying Alzheimer's candidates, including Eli Lilly's semagacestat and Elan's ELND005.

"Despite this disappointing result, Pfizer remains committed to advancing the science of Alzheimer's disease, with the ultimate goal of delivering innovative and meaningful new treatment options to patients," said Steven Romano, the head of Pfizer's medicines development group.

Pfizer and Medivation said that Dimebon was generally well tolerated in the study and a full analysis of the results will be presented at a future medical meeting. The companies added that they will also stop an ongoing open-label extension study of the drug.

Pfizer paid $225m for co-development rights to Dimebon in 2008, with another $500m in the offing if development milestones were achieved.

Medivation's lead drug is now a prostate cancer therapy, MDV3100, which is partnered with Astellas and is currently in phase III trials. The company's share price barely shifted on the news, suggesting investors had already written off Dimebon's prospects.