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Donepezil has a small effect in the treatment of dementia from Parkinson's disease

Over 30 percent of patients with Parkinson's disease (PD), which is characterized by motor tremors, develop dementia. Although dementia is associated with loss of independence and increased mortality, it is a largely untreated symptom of PD. The drug donepezil, which has been shown to improve cognition and daily functioning of patients with Alzheimer's disease, may also improve cognitive function in patients with PD, according to a new study.

Researchers, supported in part by the Agency for Healthcare Research and Quality (HS00004), found that donepezil was well tolerated among patients with PD and did not worsen their symptoms. In this study, 22 patients with PD and mild to moderate dementia were randomized into two groups. The first group received donepezil (5-10 mg/day) while the second group received a placebo that looked identical to donepezil. The treatment period lasted 10 weeks followed by a "washout" period of 6 weeks during which neither group received either donepezil or the placebo. After 6 weeks, patients in the first group who originally received the donepezil received the identical placebo, while the second group of patients received the donepezil. Again, the treatment period was 10 weeks.

The primary outcome measure was the Alzheimer's Disease Assessment Scale Cognitive Subscale (ADAScog). Researchers found that donepezil was well tolerated in 81 percent of patients and most adverse events were mild. There was no worsening of total or motor PD symptoms as measured by the Unified Parkinson's Disease Rating Scale. Donepezil had a modest effect on cognitive function. Although this is a small study, it is the largest reported randomized, blinded, placebo-controlled clinical trial of a cholinesterase inhibitor for PD-related dementia.

More details are in "Donepezil for dementia in Parkinson's disease: A randomized, double blind, placebo controlled, crossover study," by Bernard Ravina, M.D., Mary Putt, Sc.D., Andrew D. Siderowf, M.D., and others, in the July 2005 Journal of Neurology, Neurosurgery, and Psychiatry 76, pp. 934-939.

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