Donepezil (Aricept), a drug used for treating people with Alzheimer’s disease, may also improve the thinking ability of   Parkinson’s patients who have developed dementia - a common problem with this disorder, researchers said on Wednesday.

However, the results show that while donepezil is a safe and well-tolerated treatment for Parkinson’s-related dementia, it only provides modest improvements in mental capacity.

Given the drug’s effects in Alzheimer’s patients, it was thought that donepezil might also benefit Parkinson’s patients. However, the drug does have certain chemical properties that could, in theory, worsen the movement problems commonly seen with Parkinson’s disease.

Dr. B. Ravina, from the National Institutes of Health in Bethesda, and colleagues compared the effects of donepezil and placebo in 22 Parkinson’s patients with dementia. The subjects were treated with donepezil or placebo each day for 10 weeks and then, after a 6-week “washout” period, with the other agent for 10 weeks.

In the study, which is reported in the Journal of Neurology, Neurosurgery, and Psychiatry, donepezil was not significantly better than inactive “placebo” at improving thinking ability on a variety of standard tests. However, on two tests, donepezil did outperform placebo.

Moreover, there was no evidence that the drug aggravated any Parkinson’s symptoms as feared.

Parkinson’s disease Symptoms
Parkinson’s disease usually begins as a slight tremor or stiffness involving the arm or leg on one side of the body. The tremor is prominent at rest and is regular, typically occurring at a rate of three to six times per second. The Parkinson’s disease tremor usually worsens under stress, improves when the arm or leg is moved voluntarily, and may disappear entirely during sleep. In the earliest stages, Parkinson’s disease may be evident only as a tremor involving the thumb and index finger. This tremor sometimes is called “pill-rolling” tremor because it looks as if the person is manipulating a small object such as a pill.

As the illness progresses, the tremor may become more widespread, and eventually affect limbs on both sides of the body. Handwriting may become small, shaky and eventually illegible. In addition to the classic tremor, Parkinson’s disease often causes stiffness or rigidity in the muscles of the arms or legs and a slowing of body movements (bradykinesia).

“Additional research is needed to determine whether all (drugs like donepezil) are of equal efficacy in this setting, the duration of benefit to be expected, and the interaction with (other) drugs commonly used in this patient population,” Dr. Jeffrey L. Cummings, from the University of California at Los Angeles, notes in a related editorial.

SOURCE: Journal of Neurology, Neurosurgery, and Psychiatry, June 2005.