Optimer Pharmaceuticals Receives Milestone Payment from Cempra for Next-Generation Macrolide Antibiotic

SAN DIEGO, CA - JULY 8, 2010 - Optimer Pharmaceuticals, Inc. (NASDAQ:OPTR) today announced it has received a $500,000 milestone payment from Cempra Pharmaceuticals, Inc. pursuant to the terms of a licensing agreement between the companies.  The milestone payment was made as a result of Cempra’s continuing development of a next-generation macrolide (CEM-101) for the treatment of respiratory infections. Cempra licensed CEM-101 from Optimer and has successfully completed a Phase 1 study. 

“The successful completion of the CEM-101 Phase 1 study further validates our OPopS™ drug discovery platform. We are pleased to see this compound progress into the next phase of development by Cempra,” said Pedro Lichtinger, Optimer’s President and CEO.

CEM-101 is a next-generation oral macrolide entering Phase 2 clinical development for the treatment of community-acquired bacterial pneumonia (CABP). Cempra has exclusive worldwide rights, except in Association of Southeast Asian Nations, or ASEAN, countries, from Optimer to discover, develop and commercialize macrolides from a library of more than 500 compounds, including CEM-101, originated from Optimer’s OPopS drug discovery platform.

In vitro and in vivo studies of CEM-101 have shown potent activity against S. pneumoniae as well as an extended spectrum of activity against community-associated methicillin-resistant Staphylococcus aureaus (CA-MRSA), M. avium and in animal models of malaria. These studies have also indicated that CEM-101 is active against atypical bacteria, such as Legionella, Mycoplasma and Ureaplasma and against gonococci and other organisms that cause genitourinary tract infections.

About OPopS™

Optimer’s OPopS drug discovery platform allows the development of potential drug candidates through carbohydrate mediated medicinal chemistry and enables the rapid synthesis of a wide variety of proprietary molecules. It includes GlycoOptimization, which enables the modification of a carbohydrate group on an existing drug to improve its properties, and De Novo Glycosylation, which introduces new carbohydrate groups on existing drugs to create new patentable compounds with improvement of pharmacokinetics.

About Optimer Pharmaceuticals

Optimer Pharmaceuticals, Inc. is a biopharmaceutical company focused on discovering, developing and commercializing innovative anti-infectives to treat serious infections and address unmet medical needs. Optimer has two late-stage anti-infective product candidates under development. Fidaxomicin is a narrow spectrum antibiotic being developed for the treatment of Clostridium difficile infection (CDI).  In two Phase 3 trials completed by Optimer to study the safety and efficacy of fidaxomicin for the treatment of CDI, fidaxomicin was statistically superior to vancomycin in global cure rate (defined as cure with no recurrence within four weeks of completing therapy) as well as statistically superior in reducing recurrences of CDI by up to 50% when compared with vancomycin, the only FDA approved product for CDI. Pruvel™ is a prodrug in the fluoroquinolone class of antibiotics being developed as a treatment for infectious diarrhea.  Optimer has also successfully completed two Phase 3 trials with Pruvel.  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 CEM-101, Cempra’s development plans and Optimer’s OPopS™ drug discovery technology. 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 or Cempra’s 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 or Cempra’s respective businesses including, without limitation, risks relating to: the timing, progress and likelihood of success of Cempra’s research and development efforts and clinical trials of CEM-101 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

Canale Communications, Inc.

Kim Richards

619-849-5377