Eisai, Japan's fourth-largest drug maker, said it is discussing the study's results with regulators and believes the drug's benefits still outweigh its risks in patients with Alzheimer's disease.

No patients died among a comparison group getting a placebo, Eisai said Thursday.

Aricept, which is sold in 60 countries, is approved for mild to moderate Alzheimer's disease in the United States, where Tokyo-based Eisai promotes the product with Pfizer, the world's biggest drug maker.

Improved Cognitive Function

Eisai, Japan's fourth-largest drug maker, said it is discussing the study's results with regulators and believes the drug's benefits still outweigh its risks in patients with Alzheimer's disease. Aricept and the Aciphex ulcer treatment account for more than two-thirds of sales for Eisai, whose US offices are in Teaneck.

The study found that Aricept was no better than a placebo in improving the overall functioning of patients with vascular dementia, a common form of cognitive decline that results from narrowing and blockage of arteries that supply blood to the brain. The drug, also known as donepezil, did improve cognitive function, Eisai said.

"What we're seeing is an unexpectedly low mortality rate in the placebo group," said Judee Shuler, a spokeswoman for Eisai. "We have an application pending with the FDA and are engaging in discussion."

Pfizer spokeswoman Shreya Prudlo deferred comment to Eisai.

Most Were Taking Other Medications

The death rate for the 648 patients in the study who were given Aricept was 1.7 percent, the same as in a combined analysis of two previous studies of the drug for vascular dementia, Eisai said.

In all three studies, the majority of patients had a history of stroke or heart disease, or both, and most were taking other medications, most often cardiovascular drugs.

The death rate is lower than that in the general population of patients who have the condition, the Eisai said.

The drug is approved to treat vascular dementia in India, New Zealand, the Philippines, Romania, South Korea and Thailand.