Side effects mar Elan and Wyeth Alzheimer's trial

By Julie Steenhuysen

CHICAGO (Reuters)- Keenly awaited details on Elan (ELN.I) and Wyeth's (WYE.N) new Alzheimer's drug bapineuzumab show it raised the risk of a potentially serious side effect, especially in people with a genetic risk of the disease, the companies said on Tuesday.

They said 12 people with mild-to-moderate Alzheimer's, who were treated with the drug, developed a build-up of fluid in the brain called vasogenic edema.

Ten of those cases were in people who have the ApoE4 gene, which significantly raises their risk of developing Alzheimer's disease. The other two were in non-carriers of the gene.

"Usually this occurred after the first or second dose," Dr Ronald Black, assistant vice president in neuroscience research at Wyeth, said in an interview. "About half of them had no symptoms at all, and about a third had minor symptoms."

Black said the side effect appeared to be "strongly related" to the dose of the drug people took. "The higher doses get more," he said.

None of those who received a placebo developed the brain-swelling condition. All those who suffered the side effect recovered from it, Black said.

The update on the antibody medicine, also known as AAB-001, has been closely watched by investors. If proven to work, the drug could be the first to modify the course of Alzheimer's disease, rather than just offering symptom relief.

Some analysts have forecast eventual annual sales of $13 billion (6.56 billion pounds).