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Idenix Pharmaceuticals Announces Update on Development Program for Its Lead HCV Nucleotide Prodrug Candidate, IDX20963

Idenix Pharmaceuticals Announces Update on Development Program for Its Lead
HCV Nucleotide Prodrug Candidate, IDX20963

CAMBRIDGE, Mass., June 20, 2013 (GLOBE NEWSWIRE) -- Idenix Pharmaceuticals,
Inc. (Nasdaq:IDIX), a biopharmaceutical company engaged in the discovery and
development of drugs for the treatment of human viral diseases, today
announced the Company has received verbal communication from the U.S. Food and
Drug Administration (FDA) requesting additional preclinical safety information
for IDX20963, Idenix's lead uridine nucleotide prodrug candidate. Initiation
of clinical trials for IDX20963 is on hold and the Company must provide a
satisfactory response to the FDA before clinical trials can begin in the
United States. As a result, the Company anticipates a delay in the initiation
of the clinical program for IDX20963 while it responds to the FDA's comments.
Idenix recently submitted an Investigational New Drug (IND) application for
IDX20963 to the FDA, including preclinical data demonstrating potent,
pan-genotypic activity.

ABOUT HEPATITIS C

Hepatitis C virus (HCV) is a common blood-borne pathogen infecting three to
four million people worldwide annually. The World Health Organization (WHO)
estimates that more than 170 million people worldwide are chronically infected
with HCV, representing a nearly 5-fold greater prevalence than human
immunodeficiency virus.

ABOUT IDENIX

Idenix Pharmaceuticals, Inc., headquartered in Cambridge, Massachusetts, is a
biopharmaceutical Company engaged in the discovery and development of drugs
for the treatment of human viral diseases.Idenix's current focus is on the
treatment of patients with HCV infection. For further information about
Idenix, please refer to www.idenix.com.

FORWARD-LOOKING STATEMENTS

This press release contains "forward-looking statements" for purposes of the
safe harbor provisions of The Private Securities Litigation Reform Act of
1995, including but not limited to the statements regarding the Company's
future business and financial performance.For this purpose, any statements
contained herein that are not statements of historical fact may be deemed
forward-looking statements.Without limiting the foregoing, the words
"expect," "plans," "anticipates," "intends," "will," and similar expressions
are also intended to identify forward-looking statements, as are expressed or
implied statements with respect to the Company's potential pipeline
candidates, including any expressed or implied statements regarding the
efficacy and safety of IDX20963 and the likelihood of any future clinical
trials involving IDX20963.Actual results may differ materially from those
indicated by such forward-looking statements as a result of risks and
uncertainties, including but not limited to the following: there can be no
guarantees that the Company will advance IDX20963 or other clinical product
candidate to the clinic, to the regulatory process or to commercialization;
management's expectations could be affected by unexpected regulatory actions
or delays; uncertainties relating to, or unsuccessful results of, clinical
trials, including additional data relating to future clinical trials
evaluating its product candidates; the Company's ability to obtain additional
funding required to conduct its research, development and commercialization
activities; changes in the Company's business plan or objectives; competition
in general; and the Company's ability to obtain, maintain and enforce patent
and other intellectual property protection for its product candidates and its
discoveries.Such forward-looking statements involve known and unknown risks,
uncertainties and other factors that may cause actual results to be materially
different from any future results, performance or achievements expressed or
implied by such statements.These and other risks which may impact
management's expectations are described in greater detail under the heading
"Risk Factors" in the Company's quarterly report on Form 10-Q for the quarter
ended March 31, 2013 as filed with the Securities and Exchange Commission
(SEC) and in any subsequent periodic or current report that the Company files
with the SEC.

All forward-looking statements reflect the Company's estimates only as of the
date of this release(unless another date is indicated) and should not be
relied upon as reflecting the Company's views, expectations or beliefs at any
date subsequent to the date of this release.While Idenix may elect to update
these forward-looking statements at some point in the future, it specifically
disclaims any obligation to do so, even if the Company's estimates change.

CONTACT: Idenix Pharmaceuticals
         Teri Dahlman, (617) 995-9807

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