MIAMI BEACH — Neither donepezil nor vitamin E significantly prevented more patients with mild cognitive impairment from converting to Alzheimer's disease at 3 years than placebo, according to a study presented at the annual meeting of the American Academy of Neurology.
The randomized, controlled trial included 769 people with mild cognitive impairment (MCI). Researchers compared the number of “conversions” to Alzheimer's disease (AD) among 257 people taking 2,000 IU of vitamin E per day, 253 taking 10 mg of donepezil per day, and 259 taking placebo. The mean age was 72 years, and 46% of participants were women.
Rates of progression from MCI to AD were comparable among patients in the three treatment arms at 36 months. When researchers reassessed the data in 6-month increments, they found that people on donepezil were significantly less likely to have progressed to AD at 6 months and 1 year than those taking placebo. At 18 months, the difference was no longer significant, and then results converged with the placebo group. There were no significant differences at any 6-month measurement between vitamin E and placebo.
“Donepezil appears to reduce the risk of progressing from MCI to Alzheimer's disease up to 12 months,” said Leon J. Thal, M.D., professor and chair of the department of neurosciences at the University of California, San Diego, and one of the study authors.
The study is scheduled for publication in the New England Journal of Medicine on June 9. (An online preview was posted at www.nejm.org
A total of 212 patients converted from MCI to AD during the study. About 16% of patients treated with placebo converted each year, or more than 45% by the study's end. One patient progressed to mixed dementia, and another converted to primary progressive aphasia.
Secondary outcomes included cognition and function. There were very few significant differences between vitamin E and placebo, except in scores for executive, language, and overall cognitive scores; these differences were only significant in the first 18 months. However, “donepezil had a [greater] effect on overall function, memory, and language up to 18 months,” Dr. Thal said. Six of seven mental-scoring differences were only significant during the first 18 months of the study.
A genetic factor made a significant difference in conversion of MCI to Alzheimer's disease: ϵ4 allele status for apolipoprotein E (apoE). About 55% of participants tested positive for one or more apoE ϵ4 alleles. “Positives converted at a higher rate and accounted for 76% of conversions,” said Dr. Thal, who is also principal investigator for his university's Alzheimer's disease research center.
Donepezil made a significant difference in participants positive for the allele, compared with placebo, at 12, 24, and 36 months. Most of the treatment effect of donepezil occurred among the apoE ϵ4 carriers.
David S. Knopman, M.D., discussed the study findings in a subsequent presentation at the meeting. “My thinking is that [apoE ϵ4] genotyping should not be done prior to initiating therapy with donepezil in people with MCI, he said.” Dr. Knopman is professor of neurology at the Mayo Clinic, Rochester, Minn., and had no conflict of interest to report.
“Are we there yet? Should MCI be treated with donepezil?” Dr. Knopman asked. “We need to discuss these results with families and give them both views.” On the negative side, treatment with donepezil is not cost effective. On the plus side, the drug provides a 58% 1-year risk reduction “that may be clinically meaningful to some patients and families.”