Biotechnology company Medivation Inc. said Thursday a midstage study testing its Dimebon treatment for Alzheimer's showed the drug was significantly effective, sending shares soaring in morning trading.

Shares surged $2.25, or 37 percent, to $8.30 on the American Stock Exchange.

The Phase II clinical trial involved 183 patients with mild to moderate Alzheimer's disease at 11 sites in Russia. The drug met all five of its efficacy endpoints, which included different measurement scales for improvement in the disease, during the six-month, randomized and double-blind study.

Results also showed the drug was well tolerated with mild side effects.

"We believe that these results are important, in part because the primary and key secondary efficacy endpoints used in this trial are accepted by the Food and Drug Administration for registration of drugs to treat mild to moderate Alzheimer's disease," said Dr. David Hung, Medivation president and chief executive, in a statement.

The company has also started an extension study on the drug, which allows patients to continue treatment for up to a total of 12 months. Those results are expected in the second quarter of 2007.

Dimebon is also being studied for possible use in treating Huntington's disease.