NEW YORK ( TheStreet) -- Pfizer ( PFE - Get Report) announced late Monday the failure of its experimental Alzheimer's disease drug bapineuzumab in a late-stage clinical trial.

Bapineuzumab is being co-developed by Johnson & Johnson ( JNJ - Get Report) with certain economic rights held by Irish drug maker Elan ( ELN). Investors widely expected bapineuzumab clinical trials to fail based on similarly poor results from mid-stage studies presented in July 2008.

The study announced Monday enrolled patients with mild to moderate Alzheimer's who also carried a gene known as ApoE4 that confers a higher risk of developing the disease. Patients treated with bapineuzumab showed no cognitive or functional improvement compared to patients treated with a placebo, Pfizer said.

Three other phase III studies of bapineuzumab, enrolling both Apoe4 carriers and non carriers, are still underway with results expected later this year.

Elan shares are down 16% to $11.26 in Monday after-hours trading.

--Written by Adam Feuerstein in Boston.

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