CHICAGO (Reuters) -
A drug for Alzheimer's disease made by
Medivation Inc kept symptoms at bay for 18 months, U.S.
researchers said on Wednesday, but people who got the drug
after first taking a placebo fared less well, suggesting early
treatment is best.

The latest results, being presented at the Alzheimer's
Association's international meeting in Chicago, found Dimebon
was safe and continued to benefit people who took it for a year
and a half.

“The most important thing from my point of view is there
were no new safety issues that emerged with longer exposure of
the patients,” said Dr. Jeffrey Cummings of UCLA, who helped
with the study.

The results from the 183-patient study conducted in Russia
found people continued to improve, with benefits seen in
cognition, memory, activities of daily living and behavior.

The study also found that people who were treated with a
placebo for a year and then took Dimebon stabilized across five
measures of thinking ability, but were unable to catch up to
the group who had taken it for the full 18 months.

“People initially treated with the placebo and then crossed
over to Dimebon did not show the same level of benefit as those
people who took Dimebon for the full 18 months,” Cummings said
in a statement.

“This emphasizes the benefit of earlier treatment and
suggests the possibility that Dimebon may slow the progress of
Alzheimer's,” he said.

Medivation has provided frequent updates of patients in the
study in Russia, where patients in the study took few if any
drugs other than Dimebon.

Such a study would not be possible in Western countries,
where most Alzheimer's patients take a variety of other drugs.

Some doctors think the true test of whether Dimebon
represents an advance over current therapies will come from
studies done in the West, where patients have ready access to
other drugs that can slow progression of the disease.

These include Eisai Co Ltd's and Pfizer Inc's Aricept,
Forest Laboratories Inc's Namenda, Novartis AG's Exelon and
Johnson & Johnson's Razadyne.

All affect message-carrying chemicals in the brain called
neurotransmitters, but lose their effect over time.

“The one issue with this trial is that no other treatments
were allowed,” Dr. Scott Turner, incoming director of the
Memory Disorders Program at Georgetown University Medical
Center in Washington, said in a telephone interview.

“Here it will be tested as an add-on, and the question is
will it have any other benefit (when taken) with the current
therapies,” he said. “I think that is a big if.”

Cummings thinks the drug has a shot.

“I think we will continue to see an effect because the
signal was strong; but under the circumstances of a global
trial, it will likely be not as clearly seen as it was in the
Russian trial,” he said in a telephone interview.

In late afternoon Nasdaq trading, Medivation shares were
down 84 cents or 4.3 percent to $18.93.

(Editing by Gerald E. McCormick)