Updated from 7:03 a.m. EDT

Elan ( ELN) and Wyeth ( WYE) are eliminating the highest dose of their Alzheimer's drug bapineuzumab from two phase III studies after independent safety monitors concluded that patients were at risk for developing swelling of the brain, the companies announced Thursday.

The two phase III studies affected are enrolling mild to moderate Alzheimer's patients who don't carry a gene known as ApoE4 that is known to increase the risk of developing the disease.

The need to remove the highest dose of bapineuzumab from studies enrolling Alzheimer's patients who are "non-carriers" of the ApoE4 gene indicates that the risk of potentially dangerous brain swelling, or vasogenic edema, is more widespread than Elan and Wyeth originally anticipated.

These patients weren't considered to be at high risk for the complication, based on safety data from an earlier phase II study of bapineuzumab.

Two other phase III studies of bapineuzumab in patients carrying the ApoE4 gene aren't affected. These studies are testing a single, lower dose of the drug, in part, because it was already known that ApoE4 "carriers" had an increased risk for brain swelling.

The decision to alter the ongoing phase III studies was made by an independent safety monitoring committee after a review of reports of vasogenic edema in patients. Elan and Wyeth didn't disclose how many patients were adversely affected.

The highest of three doses of bapineuzumab, 2.0 mg/kg, is being dropped from these studies. Patients treated with two lower doses of the drug will continue and patients currently on the high dose of bapineuzumab will switch to a lower dose.

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