Updated from 9:13 a.m. EDTShares 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.