Pfizer and partner Medivation have announced results from a Phase III trials which show that the investigational Alzheimer's disease drug Dimebon performed no better than placebo.

In the 598-patient CONNECTION trial, Dimebon (latrepirdine) did not meet its co-primary or secondary efficacy endpoints compared to placebo. Specifically, no statistically significant improvements were achieved on cognition, global function, activities of daily living or behaviour. Pfizer and Medivation added that Dimebon was well tolerated in both the CONNECTION and a separate Phase III safety and tolerability study, when dosed alone or in combination with approved Alzheimer’s medicines but observers believe that further development is in doubt.

Briggs Morrison, senior vice president of clinical development at Pfizer's primary care business unit, said that after reviewing the data, the firm “will be in a position to determine appropriate next steps regarding the Dimebon programme”. The drug, which is also being developed as a treatment for Huntington disease, is being studied in four other Phase III studies, which are currently enrolling.

Medivation chief executive David Hung acknowledged that the results “are unexpected, and we are disappointed for the Alzheimer’s community”. He added that “we are working with our colleagues at Pfizer to better understand the CONNECTION data” and will present them at an upcoming medical meeting.

Investors seem to have made their mind up and shares of Medivation lost two-thirds of their value, plummeting to $13.10. Rodman & Renshaw analysts downgraded the stock to "market perform" from "market outperform’, saying “the companies should stop any further development activity for the drug, in our view”.

The news that yet another Alzheimer’s drug candidate appears to have fallen by the wayside at the Phase III stage will increase the spotlight on bapineuzumab, under study by Pfizer and Johnson & Johnson, which took on development of the drug from Elan Corp.