Pfizer writes off $725M Dimebon pact after final Phase III failure

The last flickering hope that Medivation's Dimebon could help Alzheimer's disease patients has just been extinguished. The biotech announced this morning that a 12-month study of the drug failed to register significant improvements for patients, mirroring two shorter Phase III studies in which Dimebon failed to outperform a sugar pill. Pfizer ($PFE) took the opportunity to bow out of its partnership, writing off its $225 million upfront and $500 million milestone program for what proved to be another embarrassing pipeline failure.

In 2008, Dimebon looked like an odds-on success, with positive data from a Russian study and 10 years of sales experience to underscore its safety. But Medivation ($MDVN) was shaken to the core when its first late-stage study ended in failure, with an additional pratfall for Huntington's disease to cap the disaster.

In the end, Dimebon's failure helped tarnish the reputation of Russian drug studies while raising severe doubts about Medivation. But the company and CEO David Hung managed to turn attention to MDV3100 for prostate cancer, with positive data reigniting hope in the biotech's future and reviving its battered share price. Pfizer, meanwhile, says it won't give up on Alzheimer's, which is one of the most difficult fields in drug development.

"We recognize Alzheimer's is a very complex disease," said Pfizer's Dr. Steven J. Romano. "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."

Shares of Medivation declined slightly this morning, indicating the market's near-zero expectations for Dimebon.

- here's the press release