Optimer Pharmaceuticals ( OPTR) proves that even in a bear market, small biotech stocks are still capable of doubling in price overnight.

Shares of Optimer, a pick in my Biotech Select model portfolio, soared 90% Monday night after the San Diego-based company reported positive top-line results from a pivotal phase III study of its experimental antibiotic OPT-80 in patients infected with the hospital-borne infection Clostridium difficile.

OPT-80 achieved cure rates that are statistically equivalent to Vancocin, the only Food and Drug Administration-approved treatment for Clostridium difficile, or C. diff for short. Better yet, OPT-80 significantly reduced the recurrence of C. diff compared to Vancocin, which is marketed by Viropharma ( VPHM).

C. diff is a scary bacterial superbug that causes severe abdominal pain, bloating and diarrhea. In severe cases, the C. diff bug can rupture colons, cause blood infections and lead to death.

Like the better publicized staph infection known as MRSA, the rate of new and recurrent C. diff infections are on the rise across the U.S. and the rest of the world. Hospitals are struggling to keep new infections under control. Two antibiotics used to treat C. diff -- Vancocin and metronidazole (used off label) -- do a relatively good job of curing patients, but the relapse rate -- once treatment ends -- is high.

Biotech Select

Optimer's experimental drug OPT-80 is designed to match the cure rate of the current C. diff drugs with a more convenient twice-daily dosing schedule. More importantly, earlier data suggests that OPT-80 could significantly cut the recurrence rate of C. diff infections.

According to the top-line results from the phase III study announced Monday night, 88% of patients treated with OPT-80 achieved a clinical cure compared to 86% of patients treated with Vancocin.

Patients were treated with OPT-80 twice daily for 10 days. Vancocin was dosed four times daily, also for 10 days. A clinical cure was defined as patients requiring no further therapy for C. diff two days after completing treatment.

A key secondary endpoint of the study measured the recurrence, or relapse rate. Here, too, OPT-80 excelled, with just 15% of patients reporting a recurrence of the C. diff infection four weeks after treatment compared to a 25% recurrence rate reported for patients treated with Vancocin.

Optimer's phase III study was designed to show statistically non-inferior efficacy of OPT-80 compared to Vancocin on both the primary endpoint (cure rate) and the secondary endpoint of recurrence rate. The fact that OPT-80 was numerically superior on both endpoints is a big win for the drug.

Recurrence of C. diff infection in treated patients is a growing problem, so the lower recurrence rate for OPT-80 makes a strong case for using the drug as a first-line treatment.

A second phase III study of OPT-80 in C. diff patients is ongoing with data expected in the second half of 2009. Optimer also said it plans to resurrect partnering discussions for OPT-80. In 2007, an experimental antibiotic from Genzyme ( GENZ) failed a closely watched phase III study.

Optimer shares closed Monday at $4.60 prior to the release of the OPT-80 study results. That news sent the stock up 90% to $8.75 in the after-hours session.


Know What You Own: In Tuesday's early trading, other top biotech performers include Genetic Technologies ( GENE), Targacept ( TRGT), Cytokinetics ( CYTK) and BioDelivery Sciences ( BDSI).
At the time of publication, Feuerstein's Biotech Select model portfolio was long Optimer Pharmaceuticals.

Adam Feuerstein writes regularly for TheStreet.com. In keeping with TSC's editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet.com. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.