Optimer Pharmaceuticals Completes Enrollment in Second Fidaxomicin Phase 3 Clinical Trial in Patients With Clostridium difficile Infection

Optimer Pharmaceuticals Completes Enrollment in Second Fidaxomicin Phase 3
Clinical Trial in Patients With Clostridium difficile Infection

SAN DIEGO, Nov. 12 /PRNewswire-FirstCall/ -- Optimer Pharmaceuticals, Inc.
(Nasdaq: OPTR) today announced that it has completed enrollment in the second
of two pivotal Phase 3 clinical trials evaluating the safety and efficacy of
fidaxomicin (OPT-80) for the treatment of Clostridium difficile infection, or
CDI.

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"Completing enrollment in the second Phase 3 trial is a major milestone in the
development of fidaxomicin. The two fidaxomicin trials combined represent the
largest CDI database in the world, and will be an important tool for the
medical community in understanding the epidemiology of this infection," said
Michael N. Chang, Ph.D., President and CEO of Optimer. "We will complete the
analysis of the data from this trial and we expect to report top-line results
in the first quarter of 2010."

The Company previously reported positive data from the first Phase 3 trial
which showed that fidaxomicin met its primary endpoint of non-inferiority of
clinical cure compared to Vancocin®. In addition, patients treated with
fidaxomicin in the first Phase 3 trial experienced a reduction in CDI
recurrence compared to Vancocin (p=0.004) and had a higher global cure (cure
with no recurrence within four weeks) compared to Vancocin (p=0.006). If the
results of this second study are also positive, the Company expects to use
these studies as a basis for a New Drug Application filing in 2010.

Fidaxomicin Clinical Study Design

The second Phase 3 trial is a multi-center, randomized, double-blind clinical
trial comparing the safety and efficacy of fidaxomicin (200 mg q12h) to that
of oral vancomycin (125 mg q6h) in subjects suffering from CDI. This study,
which enrolled 536 adult subjects providing 90% power to assess the primary
endpoint of clinical cure, was conducted in approximately 100 clinical sites
throughout North America and Europe. The study is designed to evaluate safety
and compare the response to treatment by subjects during and after a 10-day
course of therapy for cure, which is the primary endpoint. If cured, subjects
are followed for a subsequent four-week period to evaluate recurrence, which
is a secondary endpoint. Global cure, defined as cure with no recurrence, is
also a secondary endpoint.

About Clostridium Difficile Infection

CDI has become a significant problem in hospitals, long-term care facilities
and in the community. It is a serious illness caused by 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. CDI typically develops from the use of broad-spectrum
antibiotics that disrupt normal gastrointestinal (gut) flora, allowing C.
difficile bacteria to flourish.

Current therapeutic options for CDI include the off-label use of metronidazole
or oral vancomycin, the only FDA approved treatment for CDI. However,
approximately 20% to 30% of CDI patients who initially respond to these
treatments experience a clinical recurrence following cessation of antibiotic
administration.

Primary risk factors for CDI include broad-spectrum antibiotic use, advanced
age (over 65), emerging hyper-virulent strains (BI/NAP1/027, 078, 001) of C.
difficile, and previous exposure to CDI that lead to recurrence. Higher
incidence, increased treatment failures, and recurrence with standard
therapies have resulted in greater awareness and concern of CDI among medical
professionals and public health officials.

About Fidaxomicin

Fidaxomicin is the first in a new class of antibiotics called macrocyclics,
which inhibit the bacterial enzyme RNA polymerase, resulting in the death of
Clostridium difficile. The narrow spectrum profile of fidaxomicin may
eradicate Clostridium difficile selectively with minimal disruption to the
normal intestinal flora. This may facilitate the return of the normal
physiological conditions in the colon and reduce the probability of CDI
recurrence.

About Optimer Pharmaceuticals

Optimer Pharmaceuticals, Inc. is a biopharmaceutical company focused on
discovering, developing and commercializing innovative anti-infective products
to treat serious infections and address unmet medical needs. Optimer has two
late-stage anti-infective product candidates under development. Fidaxomicin,
formerly known as OPT-80, is the only antibiotic therapy currently in Phase 3
worldwide clinical development for Clostridium difficile infection.
Pruvel(TM) (prulifloxacin) is an antibiotic which has completed two Phase 3
clinical trials for the treatment of infectious diarrhea in travelers.
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 ability of fidaxomicin to treat CDI and address
current treatment limitations, expected regulatory filings and announcements
of clinical data. 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 its product research and development programs and
clinical trials, the timing and status of its preclinical and clinical
development of potential drugs, the process of preparing and submitting
regulatory filings with the FDA and other risks detailed in Optimer's filings
with the Securities and Exchange Commission.

Contacts

Optimer Pharmaceuticals, Inc.
John Prunty, CFO & VP, Finance
Christina Donaghy, Corporate Communications Manager
858-909-0736

Porter Novelli Life Sciences
Jason I. Spark, Vice President
619-849-6005

SOURCE Optimer Pharmaceuticals, Inc.

John Prunty, CFO & VP, Finance, or Christina Donaghy, Corporate Communications
Manager, both of Optimer Pharmaceuticals, Inc., +1-858-909-0736; or Jason I.
Spark, Vice President of Porter Novelli Life Sciences, +1-619-849-6005