Controversy Shadows Medivation (Update)

Updated from 9:30 a.m. EDT

Shares of Medivation traded moderately higher Tuesday, one day after the biotech company announced that its experimental drug Dimebon improved the mental status of patients with Huntington's disease, according to results of a phase II study.

The positive news was not without controversy, however, which may be dampening investor enthusiasm.

Shares of the San Francisco-based company jumped as much as 22% to $14.70 in after-hours trading Monday, but selling pared back the gain, leaving the stock up just 3% at $12.42 in recent trading Tuesday.

Patients treated with Dimebon over three months showed a statistically significant improvement in cognition compared to placebo patients, as measured by the Mini-Mental State Examination (MMSE), a commonly used test of mental status, Medivation said.

Dimebon-treated patients also demonstrated positive improvement on the behavioral component of the United Huntington's Disease Rating Scale (UHDRS), although this result was not statistically significant.

The UHDRS also measures cognitive changes in Huntington's patients, but here, Dimebon apparently had no effect.

The data were noteworthy because there are no drugs approved to treat Huntington's disease, a progressive and fatal disease that gradually kills certain brain cells, causing involuntary muscle movement, deteriorating mental status and severe behavioral disturbances.

Other drugs have shown promise treating the motor deficits associated with Huntington's, but none has been able to help patients improve cognition or behavior, according to Dr. Karl Kieburtz, neurology professor at the University of Rochester and the principal investigator of the Dimebon phase II study.