Optimer Pharmaceuticals Announces Change to Board of Directors

SAN DIEGO, July 17, 2008 - Optimer Pharmaceuticals, Inc. (Nasdaq: OPTR) today announced that Martin C. Muenchbach, Ph.D., an Investment Manager at Bellevue Asset Management AG, has notified the Company that he will be stepping down from his position as a member of the Board of Directors as of August 1, 2008.  Dr. Muenchbach joined the Board in December 2005, advising Optimer as a private company and then working with the Company in its transition to a public company.  Dr. Muenchbach’s departure is not related to relations with the board members or with the company.  Dr. Muenchbach will continue to follow his pursuits in venture capital, serving on the Board of many privately held companies. Optimer is currently in the process of identifying candidates to serve on its Board of Directors.

 “We would like to thank Martin for his many contributions and dedicated service to the Company.  His board experience and leadership have been invaluable as the company has grown from a private company through its maturation as a public company," said Michael N. Chang, Ph.D., CEO and President of Optimer.  “We wish him great success in his future endeavors.” 

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, currently in two pivotal Phase 3 clinical trials, is being developed for the treatment of Clostridium difficile infection, the most common hospital-acquired diarrhea. Prulifloxacin, also 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 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 anticipated resignation of current directors and the identification of additional directors.  Words such as "believes", "anticipates", "plans", "expects", “may”, "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, the 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