- 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.”

More information

The Alzheimer's Association has more about Alzheimer's disease.