SHAWN POGATCHNIK Associated Press Writer DUBLIN (AP) — The developers of an experimental new treatment for Alzheimer's disease, Elan Corp. and Wyeth, announced Thursday they have stopped the top dosage because trial patients are suffering from an increased risk of brain inflammation from water retention. The companies said the setback would not affect their ongoing, advanced trials to win approval for bapineuzumab, a drug designed to combat Alzheimer's, an incurable disease that destroys the brain. Elan President Carlos Paya said an independent Safety Monitoring Committee overseeing the Elan-Wyeth trials detected a higher level of vasogenic edema — water accumulating in brain tissue — in trial patients taking the highest dose, 2 milligrams. He said the committee had found no health risks in patients receiving lower doses of bapineuzumab. "Our review of the safety data and the feedback from the Safety Monitoring Committee made it clear that continued development of the highest dose was not advisable. The decision to remove the highest dose from development reduces risk to patients, and it also helps to reduce risk to the overall development effort," Moya said. Investors sold Dublin-headquartered Elan on the news. At midmorning, Elan shares were 2.6 percent lower at €4.91 ($6.53) amid broad gains on the Irish Stock Exchange. Elan said several hundred patients who had been receiving or scheduled to receive the highest dose will be removed from the trials or switched to lower doses, either 1 milligram or 0.5 miligrams. It said the problem was detected early using MRI scans on the brains of patients, who were not displaying symptoms associated with water-inflamed brains. Elan and Wyeth began third-level trials on Alzheimer's sufferers in December 2007. This is the first time they have halted treatment on any category of patients. The trials involve four groups, two of which included patients taking the highest dose. The companies said they now expected approximately 3,600 patients worldwide to participate in the trials, down from their original plan for 4,100. More than a dozen pharmaceutical and biotechnology companies are competing to develop the first viable treatment to suppress or reverse the brain-wasting effects of Alzheimer's, which affects tens of millions worldwide.