Optimer Initiates Phase 3b Clinical Trial of DIFICID® for the Prevention of Clostridium difficile-Associated Diarrhea in Bone

 Optimer Initiates Phase 3b Clinical Trial of DIFICID® for the Prevention of
 Clostridium difficile-Associated Diarrhea in Bone Marrow Transplant Patients

PR Newswire

JERSEY CITY, N.J., Nov. 1, 2012

JERSEY CITY, N.J., Nov. 1, 2012 /PRNewswire/ --Optimer Pharmaceuticals, Inc.
(NASDAQ: OPTR) today announced that the first patient has been dosed in its
DEFLECT-1, Phase 3b clinical trial of DIFICID® (fidaxomicin) tablets for the
prevention of Clostridium difficile-associated diarrhea (CDAD) in patients
undergoing hematopoietic stem cell transplant (HSCT), often referred to as
bone marrow transplantation. CDAD can be a serious complication of HSCT.

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Patients undergoing HSCT present with multiple risk factors including immune
suppression and the use of prophylactic antibiotics which make them
susceptible to CDAD; it is estimated that up to 30% of patients undergoing the
procedure will develop CDAD. HSCT patients with CDAD generally have longer
hospital stays, increased average costs and are at increased risk of death.

"By nature of the procedure, patients undergoing HSCT have weakened immune
systems and are often receiving antibiotics, both of which are significant
risk factors for the development of CDAD," said Sherwood L. Gorbach M.D.,
Optimer's Chief Scientific Officer and Senior Vice President of R&D.
"Consequently, the prevalence of CDAD in these patients is high and we believe
that DIFICID has potential to prevent CDAD in this high-risk population. We
hope that this trial will provide us data supporting this hypothesis."

This multi-center study will utilize a randomized, double-blind design to
evaluate the safety and efficacy of DIFICID as prophylaxis in individuals
undergoing HSCT. It will enroll an estimated 340 patients into two arms, one
of which will receive 200 milligrams of DIFICID daily for thirty days and the
other of which will receive a placebo, since the efficacy of CDAD prophylaxis
has not been previously determined. By using an innovative "adaptive design,"
a blinded interim analysis will be conducted after 170 evaluable subjects have
completed treatment and the 30 day post-treatment follow up to re-estimate the
sample size based on accumulated data. The primary endpoint is the incidence
of CDAD from the first dose of study drug through the 30-day follow-up period
after the last day of drug. The objective is to achieve a 60% improvement in
the CDAD incidence rate in the DIFICID group over the placebo group. Initial
data from the trial is expected in the first half of 2014.

"There are currently no demonstrated options to prevent CDAD in patients
undergoing HSCT and the incidence rate in this population suggests that the
need is very high. Pursuing a prophylaxis indication has the potential to help
a new population at risk of CDAD and is an important step in the
implementation of our life cycle management plan," said Pedro Lichtinger,
President and CEO of Optimer.

AboutClostridium difficile-associated Diarrhea (CDAD)
Clostridium difficileinfection (CDI) is a serious illness resulting from
infection of the inner lining of the colon byC. difficilebacteria, which
produce toxins that cause inflammation of the colon, severe diarrhea and, in
the most serious cases, death.Clostridium difficile-associated diarrhea is
the most common symptom of CDI. In recent years,C. difficilehas surpassed
methicillin-resistantStaphylococcus aureus(MRSA) as the leading cause of
healthcare-acquired infections in community hospitals. Patients typically
develop CDAD from the use of broad-spectrum antibiotics that disrupt normal
gastrointestinal (gut) flora, possibly allowingC. difficilebacteria to

About DIFICID® (fidaxomicin) Tablets
DIFICID is the first macrolide antibacterial drug indicated for Clostridium
difficile-associated diarrhea (CDAD) to be approved in over 25 years in the
U.S. It is indicated for the treatment of CDAD in adults 18 years of age or
older. DIFICID is administered in 200 milligram tablets given orally twice

Important Safety Information for DIFICID
DIFICID is contraindicated in patients with hypersensitivity to fidaxomicin or
to any of the excipients in the formulation. 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%).

About Optimer Pharmaceuticals
Optimer Pharmaceuticals, Inc. is a global biopharmaceutical company focused on
developing and commercializing innovative hospital specialty products that
have a positive impact on society. Optimer developed DIFICID® (fidaxomicin)
tablets, an FDA-approved macrolide antibacterial drug for the treatment of
Clostridium difficile-associated diarrhea (CDAD) in adults 18 years of age and
older and is commercializing DIFICID in the U.S. and Canada. Optimer also
received marketing authorization for fidaxomicin tablets in the European Union
where its partner, AstellasPharma Europe, is commercializing fidaxomicin under
the trade name DIFICLIR™. The Company 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 the potential of DIFICID to prevent CDAD, the safety and
efficacy of DIFICID in individuals undergoing HSCT, the sample size of the
Phase 3b clinical trial, the use of DIFICID to benefit additional populations
at risk of CDAD and Optimer's life cycle management plans for DIFICID. 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 releaseand Optimer undertakes no obligation
to update or revise these statements, except as may be required by law. Actual
results may differ materially from those set forth in this release due to the
risks and uncertainties inherent in Optimer's businessincluding, without
limitation, risks relating to:Optimer'sability to continue driving adoption
and use of DIFICID, DIFICID's ability to compete with cheaper generic
competition, whether healthcare professionals will prescribe DIFICID,the
extent to which DIFICID will be accepted on additional hospital formularies
and the timing of hospital formulary decisions, whether Optimer's hospital
contracting strategy will result in additional DIFICID prescriptions in the
hospital or retail markets, whether Rx Assist is utilized and whether it will
facilitate access to DIFICID and other risks detailed inOptimer'sfilings
with theSecurities and Exchange Commission.

Optimer Pharmaceuticals, Inc.
David Walsey, Vice President, Investor Relations and Corporate Communications

Canale Communications, Inc.
Jason I. Spark, Senior Vice President

SOURCE Optimer Pharmaceuticals, Inc.

Website: http://www.optimerpharma.com
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