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Optimer Presents Positive Data on Two Lead Anti-Infective Drug Candidates

SAN DIEGO--(BUSINESS WIRE)--Sep 20, 2007 - Optimer Pharmaceuticals, Inc. (NASDAQ:OPTR), presented data on the activity of its two lead compounds at the 47th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC).

Earlier this week, data was presented at ICAAC showing that ulifloxacin, the active metabolite of prulifloxacin, Optimer's prodrug antibiotic product candidate, has significantly higher antibiotic activity in vitro than ciprofloxacin, the current standard of care for infectious gastroenteritis, or traveler's diarrhea. This study was conducted and presented by JMI Laboratories, a contract research laboratory.

In this study, ulifloxacin's activity against eight pathogens known to cause traveler's diarrhea was compared to the activity of four commonly prescribed antibiotics: ciprofloxacin, rifaximin, ampicillin and co-trimoxazole. All bacteria were shown to be susceptible to ciprofloxacin and ulifloxacin, but ulifloxacin exhibited two to four fold greater activity compared to ciprofloxacin. Importantly, this increase in activity was observed against all targeted subgroups of E. coli, the pathogen most commonly associated with traveler's diarrhea.

"These results demonstrate a significant breadth of antimicrobial activity and support our development of prulifloxacin for the treatment of travelers' diarrhea," commented Michael N. Chang, Ph.D., Optimer's President and Chief Executive Officer. "We are advancing prulifloxacin through two pivotal Phase 3 clinical trials with the goal of bringing this compound to the U.S. market."

Optimer scientists also presented data today demonstrating the narrow spectrum of activity exhibited by lead clinical candidate, OPT-80 and its major metabolite, OP-1118, against 32 strains of bacteria which commonly populate the gastrointestinal tract. In this study, OP-1118 demonstrated similar selective in vitro antimicrobial activity against Clostridium difficile and was as active in vitro as vancomycin against Clostridium difficile. Both OPT-80 and OP-1118, which are present at levels far in excess of their MIC in the gastrointestinal tract, had limited fecal binding properties similar to vancomycin. OPT-80's selectivity may preserve the natural balance of flora in the gastrointestinal tract in patients with Clostridium difficile-associated diarrhea (CDAD) while eliminating the infection. OPT-80 is currently being investigated in two pivotal Phase 3 clinical trials for the treatment of CDAD, a severe and sometimes life-threatening infectious diarrhea.

About Optimer

Optimer Pharmaceuticals, Inc. is a biopharmaceutical company focused on discovering, developing and commercializing innovative anti-infective products for the treatment of serious infections. Optimer currently has two late-stage anti-infective product candidates. OPT-80, currently in two pivotal Phase 3 clinical trials, is being developed for the treatment of Clostridium difficile-associated diarrhea, the most common hospital-acquired diarrhea. Prulifloxacin, also currently in two pivotal Phase 3 clinical trials, is an antibiotic being developed for the treatment of travelers' diarrhea, a form of infectious diarrhea. Additional information regarding Optimer and its products can be found at

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 OPT-80 , Prulifloxacin, CDAD, and the timing of clinical trials and anticipated results and regulatory activities. 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 timing, progress and likelihood of success of our product research and development programs, the timing and status of our preclinical and clinical development of potential drugs and other risks detailed in Optimer's filings with the Securities and Exchange Commission.


Optimer Pharmaceuticals, Inc.
Christina Donaghy, Corporate Communications Manager
John D. Prunty, Chief Financial Officer & VP Finance

Posted: September 2007