Pfizer and partner Medivation are ending development of Dimebon after the drug failed in a late-stage study as a potential treatment for Alzheimer's disease.

The companies announced results from the Phase III CONCERT trial which evaluated Dimebon (latrepirdine) when added to ongoing treatment with Eisai/Pfizer's Aricept (donepezil) in patients with mild-to-moderate Alzheimer’s. The drug, which was first sold in Russia as an antihistamine, did not achieve statistically significant results for either of the two co-primary endpoints, cognitive ability or self care and daily function, in the 1,003-patient study.

Dimebon was generally well tolerated and a full analysis of the results will be submitted at an upcoming scientific congress. However, Pfizer and Medivation have already decided to discontinue development of the drug for all indications (in April 2011, it failed in Phase III as a potential treatment for Huntington disease) and will terminate the ongoing open label extension study in Alzheimer’s.

In March 2010, results from another Phase III trial showed that Dimebon performed no better than placebo. Specifically in that that 598-patient study, no statistically significant improvements were achieved on cognition, global function, activities of daily living or behaviour.

Steven Romano, head of the medicines development group at the US giant's primary care business unit, said "we recognise Alzheimer’s is a very complex disease” but “despite this disappointing result, Pfizer remains committed to advancing the science" to treat the problem.

The latest Phase III failure for Dimebon came as little surprise and Medivation ended the day down just 3.3% at $53.90 as investors had pretty much written off the project already.