"These patients seem to be declining much less, about half as much as ordinarily expected, over a 6-month period," said Barry Reisberg, M.D., lead investigator. "This medication will slow down the otherwise inexorable progress of this disease, and it is remarkably free of side effects. These are very impressive results. It looks like this drug really will have an impact on this disease."

Neil Buckholtz, Ph.D., of the National Institutes of Health, said "This study shows that treatment in the very late stages of Alzheimer's disease can be beneficial in a number of ways, for both patients and caregivers."

It isn't yet known if memantine can slow the disease for more than 6 months, said Reisberg. "It may slow the progression for a longer period of time, and we have some evidence that it does, but that remains to be definitively determined." He added that the drug may also be effective in milder forms of the disease and may have other uses in combination with other medications.

Prior to the current study, there were no treatments available for slowing the later stages of the disease. In these stages, patients begin to lose the ability to care for themselves. "This is the time when there is an increase in behavioral disturbances, and when the burden on caregivers intensifies as they struggle to care for a loved one who is slipping away," said Reisberg.

Memantine blocks the excitatory effects of glutamate. In recent years researchers have learned that when neurons become overstimulated due to an abundance of glutamate, they can be damaged or die. Reisberg noted that this "excitotoxicity" has been linked to neuronal loss in the brains of patients that results in functional losses in memory and learning. "Memantine is a completely different chemical way of getting at the disease," he said.

In the United States, currently available treatments strengthen the activity of the cholinergic system. They have proved effective in the mild to moderate stages of the disease.

The new study, led by Reisberg and Steven Ferris, Ph.D., involved 32 medical centers and 252 patients. The mean age of the patients was 76 years, and 67 percent of the participants were women. All of the patients lived independently in the community. All had trouble putting on clothing. Many also had difficulties with bathing, toileting, and continence. All of the patients could speak to some extent and were still able to walk.

In the randomized, double-blind design, patients received 10 milligrams of memantine or a placebo twice a day for 28 weeks. A battery of behavioral, cognitive, and functional tests were used to evaluate patients at the beginning and end of the study, and clinicians conducted interviews with caregivers to assess the activities of patients during the study.

Overall, the study found that the patients who were taking memantine showed significantly less deterioration in cognition and in the ability to perform daily life activities than those taking placebo pills. The side effects from the drug were minimal: Patients in the placebo group experienced more side effects than those who received memantine. No side effects were considered likely to be related to the drug.