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 approved as an antihistamine in Russia in the early 1980s attracted attention as a potential Alzheimer's treatment following positive animal studies in 2000. Study results indicate that Dimebon has a different mechanism of action that is unrelated to its antihistamine properties.

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.

Researchers believe trial results suggest a broad, general benefit affecting language, memory, and other domains of cognition.

Dimebon is not like some of the the currently approved Alzheimer's drugs, such as — Aricept, Razadyne, and Exelon — which block the activity of an enzyme in the brain called cholinesterase and are approved for the treatment of mild to moderate disease. Cholinesterase inhibitors are believed to slow down the death of neurons in the area of the brain that govern memory which are characteristic of Alzheimer's. Cholinesterase inhibitors however 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.

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. The company plans to petition the FDA for the drug's approval as an Alzheimer's treatment in 2010 if thew international study findings are consistent with the earlier studies.

SOURCES: American Academy of Neurology 60th Anniversary Annual Meeting, April 12-19, 2008.  Alzheimer's Disease Research Center, University of Pittsburgh. Lermontova, Bulletin of Experimental Biology and Medicine, 2000.