2005

Mayo Clinic Briefings — Mayo Clinic-Led Study Finds Drug Donepezil Shows Modest Slowing Effect on Progression to Alzheimer's Disease

The drug donepezil is the first to show a slowing effect — though limited — on the progression from mild cognitive impairment to Alzheimer's disease.

The randomized, double-blind, placebocontrolled study involved 769 participants and 69 medical centers in the United States and Canada, including Mayo Clinic. It compared vitamin E, donepezil, and placebo for delay or prevention of Alzheimer's disease in patients with mild cognitive impairment. Patients in the donepezil group received 5 mg per day for the first 6 weeks, then 10 mg until the study's end. Those in the vitamin E group were given 1,000 IU per day for the first 6 weeks and then 2,000 IU per day until the study's end.

Results showed that the modest slowing effect of donepezil occurred during the first 18 months of the 3-year trial, although researchers do not yet know why this was so. Over the course of the 3-year study, the patients treated with donepezil averaged 661 days until they were diagnosed as having Alzheimer's disease, while those treated with vitamin E averaged 540 days until Alzheimer's diagnosis, and those treated with placebo averaged 484 days to a diagnosis of Alzheimer's disease.

Mild cognitive impairment is considered a strong early indicator of the progression to Alzheimer's disease. Previous studies have shown that, without treatment, about 10% to 15% of individuals with mild cognitive impairment progress to Alzheimer's disease each year. Not every patient with mild cognitive impairment progresses to Alzheimer's disease, however.

The researchers conclude that donepezil has a time-limited and modest effect. While researchers do not yet know why the effect declined over time, they are encouraged by the early results and continue to search for new Alzheimer's disease treatments.