Optimer Pharmaceuticals Announces Positive Results in Prulifloxacin Phase 3 Study

SAN DIEGO– July 16, 2008 – Optimer Pharmaceuticals, Inc. (Nasdaq: OPTR) today announced positive results from its first double-blind Phase 3 trial assessing the safety and efficacy of Prulifloxacin as a once-daily (600 mg), three-day oral therapy for infectious diarrhea.

The top-line analysis of data from this study shows that Prulifloxacin met the primary endpoint of Time to Last Unformed Stool (TLUS) in both the mITT (modified intent- to-treat; n=187) and microbiologically evaluable (per protocol; n=165) populations compared to placebo.  The median TLUS for patients treated with Prulifloxacin was approximately 24 hours; this was significantly different from the TLUS for placebo with a p-value of <0.0001.  Prulifloxacin was generally well tolerated and had a similar safety profile compared to placebo.

“We are encouraged by the positive data, which shows superiority of Prulifloxacin over placebo,” said Michael N. Chang, Ph.D., President and CEO of Optimer Pharmaceuticals. “We believe these results provide a solid foundation for pursuing a New Drug Application with the FDA, assuming similar data from a second Phase 3 trial. Prulifloxacin’s short course of therapy, convenient dosing and potent bactericidal activity against a broad spectrum of gastrointestinal pathogens may make it an attractive alternative to existing treatments for infectious diarrhea.” 

Prulifloxacin Clinical Study Design

This study, referenced as OPT-099-001, was conducted at sites in Mexico and Peru and evaluated adult travelers suffering from infectious diarrhea.  This is the first of two clinical studies being carried out in preparation for a New Drug Application to the U.S. Food and Drug Administration. The patients were randomized (2:1) to receive either 600mg of Prulifloxacin once daily over three days, or placebo. Stool specimens were collected before treatment and one to three days following the end of treatment to identify enteric pathogens. 

The primary efficacy endpoint was time to the last unformed stool (TLUS), which is defined as the time in hours from the first dose of study medication to the passage of the last unformed stool.

About Infectious Diarrhea

Infectious diarrhea can be caused through infection by bacteria, viruses or parasites. Travelers’ diarrhea is infectious diarrhea contracted by the ingestion of contaminated food or water.  Symptoms include stomach cramps, vomiting, nausea, fever and headache.  Bacteria cause approximately 85% of travelers’ diarrhea which can include multiple bacteria such as E. coli, Shigella, Salmonella, or Campylobacter.  The limitations of currently available antibiotics for infectious diarrhea include limited spectrum of activity, antimicrobial resistance, possible side effects, and poor compliance, which can reduce successful outcome.

About Optimer Pharmaceuticals

Optimer Pharmaceuticals, Inc. is a biopharmaceutical company focused on discovering, developing and commercializing innovative anti-infective products for the treatment of serious infections. Optimer has two late-stage anti-infective product candidates.  OPT‑80 is being developed for the treatment of Clostridium difficile infection, the most common hospital-acquired diarrhea.  Prulifloxacin is an antibiotic being developed for the treatment of travelers’ diarrhea, a form of infectious diarrhea.  Additional information can be found at http://www.optimerpharma.com.

Forward-looking Statements

Statements included in this press release that are not a description of historical facts are forward-looking statements, including without limitation all statements related to the efficacy of Prulifloxacin as a treatment of infectious diarrhea, the timing of future clinical trials and any results thereof and expected filings with the FDA.  Words such as "believes," "anticipates," "plans," "expects," "intend," "will," "goal" and similar expressions are intended to identify forward-looking statements. The inclusion of forward-looking statements should not be regarded as a representation by Optimer that any of its plans will be achieved. Actual results may differ materially from those set forth in this release due to the risks and uncertainties inherent in Optimer's business including, without limitation, risks relating to: the development of treatments that may compete with Optimer’s drug candidates, the potential of negative factors that could arise following a full analysis of clinical trial data, the fact that past clinical results may not be indicative of future clinical results, the timing, progress and likelihood of success of Optimer’s product research and development programs, the timing and status of Optimer’s preclinical and clinical development of potential drugs and other risks detailed in Optimer's filings with the Securities and Exchange Commission.

Contacts

Optimer Pharmaceuticals, Inc.

Christina Donaghy, Corporate Communications Manager

John D. Prunty, Chief Financial Officer & VP Finance

858-909-0736

Porter Novelli Life Sciences

Jason I. Spark, Account Director

619-849-6005