Used for Decades as an Allergy Drug, Dimebon now Shows Promise in Treating Alzheimer's Patients

By Salynn Boyles

WebMD Health News

Reviewed By Louise Chang, MD

April 17, 2008 — A nearly forgotten allergy drug first used in Russia more than two decades ago is showing promise for the treatment of Alzheimer's disease.

In a study of the antihistamine Dimebon, Alzheimer's patients with mild to moderate disease continued to show improvements in memory, thinking, and daily and overall functioning over six months of treatment.

Some patients showed improvements when treated for up to a year.

Results from the Russian study were presented this week at the 60th annual meeting of the American Academy of Neurology (AAN) in Chicago. Study results were also reported last summer at an international conference on Alzheimer's disease.

Dimebon Alzheimer's Trial

Dimebon was approved as an antihistamine in Russia in the early 1980s.

It attracted attention as a potential Alzheimer's treatment following positive animal studies in 2000.

The human trial conducted in Russia included 183 patients with mild-to-moderate disease treated for six months with either Dimebon or placebo. Some patients continued to take the antihistamine for as long as a year.

Researchers reported significant improvement in memory, thinking, and other cognitive measures over placebo in as little as 12 weeks, and the differences were maintained over six months to a year.

Tests to measure mental function and interviews with caregivers confirmed improvements or disease stabilization in 81% of the Dimebon-treated patients after six months.

In a presentation delivered Thursday at the AAN meeting, Steven H. Ferris, PhD, reported that the drug's impact in Alzheimer's patients appears to be broad, rather than selective.

Ferris directs the Alzheimer's Disease Center at NYU School of Medicine.

"Our sub-analysis of the trial results suggests a broad, general benefit affecting language, memory, and other domains of cognition," Ferris tells WebMD.

International Trial Planned

The biopharmaceutical company Medivation Inc., which hopes to market Dimebon for the treatment of Alzheimer's in the U.S., is funding a second study of the drug to be conducted in the U.S., Europe, and South America.

If the earlier findings are confirmed, Medivation Inc. CEO David Hung, MD, tells WebMD that the company plans to petition the FDA for the drug's approval as an Alzheimer's treatment in 2010.

Dimebon has not been compared to the currently approved Alzheimer's drugs, but Hung says there are suggestions from the Russian study that it has a different mechanism of action that is unrelated to its antihistamine properties.

Three of the drugs — Aricept, Razadyne, and Exelon — block the activity of an enzyme in the brain called cholinesterase and are approved for the treatment of mild to moderate disease.

"What happens in Alzheimer's disease is that the neurons in the area of the brain that govern memory and thinking get sick and die," Hung says. "The cholinesterase inhibitors can slow this down, but they don't keep the cells from dying."

Early findings suggest that Dimebon may keep the neurons alive and even make sick neurons healthy again, he says.

Because many patients in the Russian trial showed improvements in memory and other aspects of mental functioning over time, there is some suggestion that the drug could modify the course of Alzheimer's disease.

Longer, rigorously designed studies would be needed to prove this, however.

Alzheimer's disease researcher Steven DeKosky, MD, who was not involved with the Dimebon research, calls the findings from the Russian study very promising. But he adds that the findings must be confirmed.

DeKosky directs the Alzheimer's Disease Research Center at the University of Pittsburgh.

"If the Russian findings hold up, that would be a big deal," he tells WebMD. "There isn't anything out there that works as well as this drug appeared to in that study. But there are still a lot of unanswered questions. We will know more when the phase III international trial is completed."

SOURCES: American Academy of Neurology 60th Anniversary Annual Meeting, April 12-19, 2008. Steven Farris, PhD, professor of psychiatry; head of the Alzheimer's Disease Center, New York University School of Medicine, New York, N.Y. David Hung, MD, president and CEO, Medivation Inc. Steven DeKosky, MD, professor and chairman, department of neurology; director, Alzheimer's Disease Research Center, University of Pittsburgh. Lermontova, Bulletin of Experimental Biology and Medicine, 2000.

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