11 patients taking Eisai’s popular Alzheimer’s disease therapy Aricept died during a clinical trial assessing the drug for vascular dementia, the Japanese drugmaker reported today.

The multicenter, randomised, double-blind study enrolled only patients with vascular dementia and no prior diagnosis for AD, and preliminary results indicate that, while improving measures of cognition, the agent failed to better global function, compared with the placebo group.

But it is the fact that 11 deaths were recorded in the 648 patients taking Aricept versus none in the 326 given a ghost pill that has triggered concern. Although Eisai stressed that the mortality rate in the placebo group is unusually low, considering the patients’ ages and pathologies, “these safety results were reported to regulatory authorities and investigators currently participating in donepezil trials,” in line with standard practice, it said a statement.

The group also noted that is has reported to global regulatory authorities worldwide that it believes the results of this vascular dementia study “do not change the overall safety profile of donepezil and that its benefit-risk profile continues to be favourable for its approved indications.”

Aricept (donepezil) is approved in several countries for the treatment of mild-to-moderate AD, including the USA where it is sold by the world’s number one drugmaker Pfizer. The product is the best-selling drug in its class, with sales of $170 million recorded by Pfizer during the first six months of 2005.

But Aricept is cleared for the treatment of vascular dementia in just a handful of territories, excluding the USA, Japan and Europe. Eisai says it plans to continue discussions with regulatory authorities regarding this indication, in the hope that eventual approval will help the drug maintain its sales momentum and stave off competition from other strong performers on the market.

In addition, the group is also seeking to market Aricept for the treatment of severe AD. This will help it to make inroads in territory currently ruled by Forest Laboratories’ Namenda (memantine) - the only drug approved to treat severe AD in the USA. Eisai and Pfizer re-filed Aricept for this indication in the USA late last year, after their initial application was rejected by the Food and Drug Administration for formatting deficiencies in the file.