Updated from 9:13 a.m. EDT

Shares of Forest Laboratories ( FRX) were dropping in midday trading after the company said its prospective treatment for Alzheimer's disease produced disappointing results in a recent study.

The company said that based on a preliminary analysis of the study, memantine administered to patients currently receiving acetylcholinesterase-inhibitor therapy for mild to moderate Alzheimer's disease didn't yield "statistically significant differences" when compared with the placebo and acetylcholinesterase treatment.

In January, Forest said the company's new drug application for memantine was accepted for filing by the Food and Drug Administration. The company said Thursday that it expects to receive an action letter from the FDA regarding the submission by the end of this year, and Forest still hopes to make memantine commercially available by mid-2004.

The company said it doesn't believe the results of the recent study will affect the memantine new-drug application. Additional analysis of the results is continuing, Forest said.

Forest's shares were losing $6.70, or 11%, to $53.91 in recent New York Stock Exchange trading.

The patients in the latest group were different than earlier memantine studies, which covered individuals with moderate to severe Alzheimer's. Among the group with mild to moderate Alzheimer's, patients receiving the combination of memantine and acetylcholinesterase "did not show a change from baseline in cognitive function" after 24 weeks of treatment, while the decline in cognitive function in patients treated with a placebo and acetylcholinesterease inhibitors wasn't as severe as expected. Forest said the difference between the two treatment groups wasn't statistically significant.

To be eligible for the recent study, patients had to have mild to moderate Alzheimer's disease and be taking a stable dose of an FDA-approved acetylcholinesterase inhibitor for at least six months.

"It may be harder to demonstrate the efficacy of combination therapy in patients with milder forms of AD when they are already being treated with an effective agent," Forest said in a press release. "In this case, the unexpected outcome that patients treated with placebo/acetylcholinesterase inhibitor did not appreciably decline in cognitive function from their baseline status would obviously make it even more difficult to show an additional benefit for the combination therapy."

More from Stocks

Pegasystems Founder Explains Why He Has One of the Hottest Tech Stocks Around

Pegasystems Founder Explains Why He Has One of the Hottest Tech Stocks Around

9 Stocks Goldman Sachs Thinks Will Blow Wall Street's Performance Away in 2019

9 Stocks Goldman Sachs Thinks Will Blow Wall Street's Performance Away in 2019

Jim Cramer on U.S.-China Trade: The Media Has it Wrong

Jim Cramer on U.S.-China Trade: The Media Has it Wrong

Is Tesla's Stock Set to Nearly Double to $500?

Is Tesla's Stock Set to Nearly Double to $500?

Tesla's $78,000 Model 3 Is a Bargain. Here's Why

Tesla's $78,000 Model 3 Is a Bargain. Here's Why