Optimer shares drop on analyst downgrades

Shares of Optimer Pharmaceuticals Inc. fell Monday as several analysts expressed concern over study results from the company's developing gastrointestinal infection drug, Fidaxomicin.

The stock fell 90 cents, or 7.7 percent, to $10.76 in afternoon trading. Shares have traded between $3.30 and $14.70 over the past 52 weeks.

On Sunday, a study investigator presented positive late-stage study results on the drug candidate at a medical conference in Finland. The results showed the treatment is as effective as ViroPharma Inc.'s Vancocin. The drugs treat a gastrointestinal infection called C. difficile, which causes diarrhea.

The full results of the late-stage study are a followup to results announced in November.

But the company also presented a subgroup analysis from the study, showing Fidaxomicin reduced recurrence rates better than Vancocin in several settings, including inpatient and outpatient, and for people both over and under 65 years of age.

The drug was no more effective at reducing recurrence from the most virulent strain of C. difficile, though.

The sub-results disappointed JMP Securities analyst Liisa Bayko, who downgraded shares to "Market Perform" from "Market Outperform" in a note to investors.

"The antibiotic appears to have a lower rate of recurrence regardless of patient age or inpatient status, however, we are disappointed that there is no difference in patients with the hypervirulent strain," she said.

She recommended investors maintain caution as more information on the key differences between Fidaxomicin and Vancocin are clarified.

Meanwhile, a Needham analyst cut the rating to "Hold" from "Buy".

ViroPharma shares gained 33 cents, or 5.9 percent, to $5.93.