SHARES IN biotech group Elan tumbled yesterday after a key Alzheimer’s drug failed the first of four key clinical trials.

The drug, bapineuzumab, failed to improve symptoms of dementia in US patients carrying a specific gene variant – ApoE4 – which is associated with the risk of developing Alzheimer’s disease, compared with those treated with a placebo.

Shares fell by close to 12 per cent in Dublin and were last night trading down 13.4 per cent in the United States. The stock suffered the biggest single loss on the FTSE Eurofirst 300 during the session, shedding 15.5 per cent to €9.38 by lunchtime.

The results were announced by Pfizer, one of Elan’s partners in the development of the drug. The company did not provide detailed results, saying they would be presented at a medical meeting in September. One of the principal investigators in the study, Dr Reisa Sperling, said there was no sign of any effect.

“There was absolutely no evidence at all of a clinical benefit of treatment on either of the primary measures, one cognitive and one functional,” said Dr Sperling, director of the Center for Alzheimer Research and Treatment at Brigham and Women’s Hospital in Boston.

Most doctors and Wall Street analysts had been expecting the drug not to succeed, since an earlier phase 2 trial had not shown a statistically significant effect. Based on the phase 2 data, bapineuzumab has a somewhat better chance of working in patients who do not have ApoE4.

Three other trials are still under way, one involving patients with the gene and two in patients without. The trials are being carried out by Pfizer and Janssen AI.

Elan has a 49.9 per cent stake in Janssen AI, which carried out the failed trial. The balance is held by Johnson Johnson.

Separately yesterday, results from Biogen Idec, which partners Elan in another critical drug, Tysabri, said sales of the drug had shown little growth year on year.

Analysts had expected the figures to show accelerating sales of Tysabri, the multiple sclerosis drug which accounts for the bulk of Elan’s revenue. Elan will report its second quarter figures today. – (Additional reporting New York Times service/Financial Times)