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The Lancet Infectious Diseases Publishes Phase 3 Study Results Confirming Superior Rate of Sustained Clinical Response of DIFICID(R) (fidaxomicin) Tablets Compared to Oral Vancomycin in Adult Patients with Clostridium difficile Infection (CDI)

- DIFICID-treated patients also experienced significantly fewer recurrences compared to vancomycin -

SAN DIEGO, March 26, 2012 /PRNewswire/ -- Optimer Pharmaceuticals, Inc. (NASDAQ: OPTR) announced today The Lancet Infectious Diseases has published results from the European and North American Phase 3 trial evaluating the safety and efficacy of DIFICID® (fidaxomicin) tablets in the treatment of adult patients with Clostridium difficile infection (CDI). The Phase 3 non-inferiority trial showed that DIFICID had similar clinical cure rates as oral vancomycin in the initial treatment of the disease. In addition, secondary endpoint analyses showed that DIFICID provided superior rates of sustained clinical response through 25 days after the end of treatment and had significantly lower recurrence rates within four weeks of treatment. The article, titled "Fidaxomicin versus vancomycin for infection with Clostridium difficile in Europe, Canada, and the USA: a double-blind, non-inferiority, randomised controlled trial," was published online ahead of print in The Lancet Infectious Diseases.

"Resolution of symptoms without recurrence is vital in the long-term management of C. difficile. We are encouraged by the results of this study that support the superiority of DIFICID in producing sustained clinical response and lowering rates of recurrence at 25 days after treatment compared with oral vancomycin," said Sherwood L. Gorbach, M.D., co-author and Optimer's Chief Scientific Officer and Senior Vice President. "To the extent treatments for CDAD can help sustain a clinical response and reduce recurrences, they would be able to offer an improvement in treatment options for patients. We look forward to conducting further research to understand how DIFICID may particularly benefit patients with continued unmet medical needs."

The results of the study showed that 87.7% of DIFICID-treated patients achieved the primary endpoint of clinical cure, defined as resolution of diarrhea and no further need for treatment, compared to an 86.8% cure rate in vancomycin-treated patients. Among patients who achieved initial clinical cure following treatment with oral vancomycin, 26.9% had a recurrence of disease within four weeks, compared with only 12.7% of patients who achieved a clinical cure with DIFICID (p =0.0002). This difference in recurrence was reflected in a statistically superior rate of sustained clinical response through 25 days after the end of treatment for the DIFICID treatment group versus vancomycin-treated patients (p=0.001).

Treatment emergent adverse events were not significantly different between groups and were primarily gastrointestinal (i.e. nausea, vomiting, diarrhea, and abdominal pain). Mortality was also similar between the two groups with a rate of 7.6% in the DIFICID-treated population and 6.5% for vancomycin.

About the Study

The Phase 3 trial was a multi-center, randomized, double-blind clinical trial, which enrolled 535 adult subjects throughout Europe and North America. Subjects with confirmed CDI received either 200 mg DIFICID (fidaxomicin) dosed orally twice daily or 125 mg vancomycin dosed orally four times daily for 10 days. This trial, known as Study OPT-80-004, is the second of two Phase 3 studies that served as the basis of approval for DIFICID by the U.S. Food and Drug Administration (FDA) in May 2011.

The objective of both studies was to show that a 10-day course of DIFICID 200 mg twice daily was at least as efficacious (non-inferior) and safe as a 10-day course of vancomycin 125 mg four times daily for the treatment of CDI. Non-inferiority in clinical cure (defined as resolution of diarrhea for the duration of treatment and patients requiring no further CDI therapy as of two days after completion of study medication) compared to vancomycin was the primary endpoint. Patients who achieved a clinical cure were monitored for a subsequent four-week period to evaluate recurrence, which was a secondary endpoint. Sustained clinical response, an exploratory endpoint, was defined as patients who were cured and did not have a recurrence during this subsequent period. The modified intention-to-treat population (mITT) was the patient group that met inclusion criteria of more than 3 unformed bowel movements in 24 hours, had a positive stool assay for toxin A or B and received at least one dose of study medication (n=509). The per protocol population was the patient group that met criteria for mITT as well as having no protocol violations, had an end-of-therapy assessment for cure, and received at least 3 days of therapy if deemed a failure or at least 8 days of therapy if deemed a cure.

About DIFICID® (fidaxomicin) Tablets

DIFICID is the first antibacterial drug indicated for Clostridium difficile-associated diarrhea (CDAD) to be approved in more than 25 years. It is indicated for the treatment of CDAD in adults 18 years of age or older. DIFICID is administered in 200 mg tablets given orally twice daily.

Important Safety Information for DIFICID

DIFICID should not be used for systemic infections. Only use DIFICID for infection proven or strongly suspected to be caused by C. difficile. Prescribing DIFICID in the absence of a proven or strongly suspected C. difficile infection is unlikely to provide benefit to the patient and increases the risk of the development of drug resistant bacteria. The most common adverse reactions are nausea (11%), vomiting (7%), abdominal pain (6%), gastrointestinal hemorrhage (4%), anemia (2%), and neutropenia (2%).

Please visit or call 855-DIFICID (343-4243) for full prescribing information for DIFICID.

About CDAD

Clostridium difficile is the most common cause of infectious diarrhea for hospitalized patients in North America and Europe , and CDAD has become a significant medical problem in hospitals, long-term care facilities and in the community. Recent data from the Agency for Healthcare Research and Quality (AHRQ) showed C. difficile cases in hospitals increased 300 percent between 1993 and 2008.

CDAD is a serious illness resulting from infection of the inner lining of the colon by C. difficile bacteria, which produce toxins that cause inflammation of the colon, severe diarrhea and, in the most serious cases, death. Patients typically develop CDAD from the use of broad-spectrum antibiotics that disrupt normal gastrointestinal (gut) flora, possibly allowing C. difficile bacteria to flourish. Older patients in particular are at risk for CDAD, potentially because of a weakened immune system or the presence of underlying disease. Approximately two-thirds of CDAD patients are 65 years of age or older. Historically, approximately 20% to 30% of CDAD patients who initially respond to treatment experience a clinical recurrence.

About Optimer Pharmaceuticals

Optimer Pharmaceuticals, Inc. is a global biopharmaceutical company focused on discovering, developing and commercializing innovative hospital specialty products that have a positive impact on society. Optimer developed and commercialized DIFICID® (fidaxomicin) tablets, an FDA-approved antibacterial drug for the treatment of adult patients with Clostridium difficile-associated diarrhea (CDAD). Optimer has also received marketing authorization for fidaxomicin tablets in the European Union under the trade name DIFICLIR™. The company is seeking marketing authorization for fidaxomicin in Canada and is exploring marketing authorization in other parts of the world where C. difficile has emerged as a serious health problem, including Asia. Additional information 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 statements related to DIFICID's ability to improve CDAD treatment options by sustaining clinical response or reducing recurrences. Words such as "believes," "would," "anticipates," "plans," "expects," "may," "intend," "will" 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. These forward-looking statements are based on management's expectations on the date of this release. 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: Optimer's ability to continue driving adoption and use of DIFICID, whether healthcare professionals will prescribe DIFICID, whether DIFICID will receive or continue to receive reimbursement coverage from healthcare payers and government agencies, the extent to which DIFICID will be accepted on hospital formularies and potential delays in formulary decisions, Optimer's ability to successfully coordinate commercialization efforts with Cubist Pharmaceuticals under its co-promotion agreement, whether Optimer will be able to realize expected benefits under its co-promotion agreement with Cubist, the fact that past results may not be predictive of future results of performance, the possibility of alternative means of preventing or treating DIFICID impacting adoption and sales of DIFICID, Optimer's ability, though its third party manufacturers and logistics providers, to maintain a sufficient supply of DIFICID to meet demand, Optimer's ability to pursue new indications for DIFICID, whether any studies intended to support additional indications for DIFICID will be successful, whether any new indications for DIFICID will be approved by the FDA and other risks detailed in Optimer's filings with the Securities and Exchange Commission. Forward-looking statements speak only as of the date of this release, and Optimer undertakes no obligation to update or revise these statements, except as may be required by law.

SOURCE Optimer Pharmaceuticals, Inc.

CONTACT: Optimer Pharmaceuticals, Inc., David Walsey, Vice President, Investor Relations and Corporate Communications, +1-858-909-0736; or Canale Communications, Inc., Jason I. Spark, Senior Vice President, +1-619-849-6005

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Posted: March 2012