MONDAY, July 28 (HealthDay News) -- It may be harder to prove the effectiveness of new Alzheimer's disease therapies, because researchers have been having a hard time finding measurable decline in memory and thinking processes in the placebo groups the drugs are being tested against, according to two new reports.
Several discoveries may explain this, according to the reports, which are expected to be presented Monday in Chicago at the Alzheimer's Association's International Conference on Alzheimer's Disease.
In the first study, researchers looked at 87 randomized, double-blind, placebo-controlled Alzheimer clinical trials conducted between 1991 and 2005. Their analysis help set conditions that may be optimal in these types of trials.
"Based on our analysis, the most reliable approach to maximize the likelihood for demonstrating efficacy is to have a placebo group size greater than 200 and to use (cognitive testing methods) at least four times and in English," researcher Dr. Lon S. Schneider, professor of psychiatry and neurology at the University of Southern California Keck School of Medicine, said in a news release issued from the conference.
The second study, which looked at trials of the drug donepezil during the 1990s, showed that the length of the placebo study may be of increasing importance. Placebo groups experienced slower declines in cognitive functions in trials done later in the decade, but this was mitigated when the trial period was longer.
"Our results indicate that patients with Alzheimer's entering the later clinical trials appear to be experiencing a slower rate of decline in memory and thinking processes," researcher Roy Jones, director of The Research Institute for the Care of Older People, in Bath, England, said in the same news release. "These observations are potentially important for the future design of clinical trials in people with Alzheimer's. For example, it may be necessary to conduct longer duration research studies -- more than 24 weeks -- to ensure any effects of treatment can be fully evaluated."
The Alzheimer's Association has more about Alzheimer's disease.
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