Idenix Pharmaceuticals, Inc. Announces Thirteen Data Presentations at the 2007 European Association For the Study of the Liver

CAMBRIDGE, Mass., March 1 /PRNewswire-FirstCall/ -- Idenix Pharmaceuticals, Inc. , a biopharmaceutical company engaged in the discovery, development and commercialization of drugs for the treatment of human viral and other infectious diseases, announced today that 13 abstracts have been accepted for presentation at the 42nd annual meeting of the European Association for the Study of the Liver (EASL), to be held in Barcelona, Spain, April 11-15, 2007. Full abstracts are available on the EASL web site (http://www.easl.ch/liver-meeting/).

Hepatitis C Abstracts

Dr. Nezam Afdhal, Chief of Hepatology at Beth Israel Deaconess Medical Center in Boston and Associate Professor at Harvard Medical School, will present “Valopicitabine (NM283), Alone or With Peg-Interferon, Compared to Peg-Interferon/Ribavirin (Peg-IFN/RBV) Retreatment in Patients With HCV-1 Infection and Prior Non-Response to Peg-IFN/RBV: One-Year Results” in a general session on Thursday April 12, 2007 between 3:00 p.m. and 4:30 p.m. Central European Time (CET).

Dr. Eric Lawitz of Alamo Medical Research in San Antonio will present “Clearance of HCV RNA With Valopicitabine (NM283) Plus Peg-Interferon in Treatment-Naïve Patients With HCV-1 Infection: Results at 24 and 48 Weeks” in a parallel session on Thursday, April 12, 2007 between 5:00 p.m. and 7:00 p.m. (CET).

Vadim Bichko, Director, Biology at Idenix Pharmaceuticals, Inc., will present “Valopicitabine (NM283) Is Fully Active Against Known HCV Protease Resistance Mutations In Vitro” in a poster session beginning on Thursday, April 12, 2007 at 7:00 p.m. CET.

Dr. Robert Ralston, Senior Director, Virology, Schering-Plough Corporation, will present “Combination of Two Hepatitis C Virus Inhibitors, SCH 503034 and NM107, Provides Enhanced Anti-Replicon Activity and Suppresses Emergence of Resistant Replicons” in a poster session beginning on Thursday, April 12, 2007 at 7:00 p.m. CET.

About Valopicitabine (NM283)

Valopicitabine is an investigational HCV RNA polymerase inhibitor being evaluated in ongoing clinical trials for the treatment of hepatitis C.

Hepatitis B Abstracts

Dr. Thierry Poynard, Professor of Medicine at the University of Paris, Hopital Pitie-Salpetriere in Paris France, will present “Sustained Off- Treatment HBeAg Response in Telbivudine and Lamivudine Treated HBeAg-Positive Patients From The GLOBE Study” in a parallel session on Friday, April 13, 2007 between 4:00 p.m. and 6:00 p.m. CET. Dr. Antonio Riva of the UCL Institute of Hepatology, University College London, UK, will present “Effector/Memory Subsets and Functionality of CD4/CD8+ T-Cells During Potent Antiviral Therapy in Chronic Hepatitis B (CHB)” in a parallel session on Saturday, April 14 between 4:00 p.m. and 6:00 p.m. CET.

Dr. Patrick Marcellin, Professor of Medicine and Head of the Viral Hepatitis Research Center at the University of Paris, Hopital Beaujon in Clichy, France, will present “76 Week Follow-up of HBeAg-Positive Chronic Hepatitis B Patients Treated with Telbivudine, Adefovir or Switched from Adefovir to Telbivudine” in a general session on Sunday, April 15, 2007 between 12:00 p.m. and 1:30 p.m. CET.

Dr. Marcellin will also present “In Hepatitis B Patients Treated with Either Adefovir or Telbivudine, Maximal Early HBV Suppression at 24 Weeks Predicts Optimal One-Year Efficacy” in a poster session beginning on Thursday, April 12, 2007 at 7:00 p.m. CET.

Dr. Rifaat Safadi of the Division of Medicine at The Hebrew University in Jerusalem, Israel, will present “A Randomized Trial of Switching to Telbivudine Versus Continued Lamivudine In Adults With Chronic Hepatitis B: Results of the Primary Analysis at Week 24" in a poster session beginning on Thursday, April 12 at 7:00 p.m. CET.

Dr. Jens Rasenack, Professor of Internal Medicine at Albert Ludwigs University, Freiburg, Germany, will present “Efficacy of Telbivudine vs Lamivudine at 2 Years In Patients With HBeAg-Positive Chronic Hepatitis B Who Are Eligible for Treatment Based on Guidelines” in a poster session beginning on Thursday, April 12, 2007 at 7:00 p.m. CET.

Dr. Ji-Dong Jia, Professor of Medicine and Director of the Hepatitis Research Center at Beijing Friendship Hospital, Beijing, China, will present “Two-Year Results of a Phase III Comparative Trial of Telbivudine vs Lamivudine in Chinese Patients” in a poster session beginning on Thursday, April 12, 2007 at 7:00 p.m. CET.

Dr. Edward Gane, Professor of Gastroenterology and Hepatology, Middlemore Hospital in Auckland, New Zealand, will present “Adefovir Salvage Therapy for Virologic Breakthrough in Telbivudine-Treated Patients from the GLOBE Study” in a poster session beginning on Thursday, April 12, 2007 at 7:00 p.m. CET.

Dr. John Wong, Professor of Medicine at Tufts University School of Medicine, Boston, will present “Cost-effectiveness of Telbivudine Versus Lamivudine for Chronic Hepatitis B” in a poster session beginning on Thursday, April 12, 2007 at 7:00 p.m. CET.

Important Information About Telbivudine

Telbivudine is indicated for the treatment of chronic hepatitis B in adult patients with evidence of viral replication and either evidence of persistent elevations in serum aminotransferases (ALT or AST) or histologically active disease. This indication is based on virologic, serologic, biochemical and histologic responses after one year of treatment in nucleoside-treatment-naive adult patients with HBeAg-positive and HbeAg-negative chronic hepatitis B with compensated liver disease.

Important Safety Information about Telbivudine - Lactic acidosis and severe hepatomegaly with steatosis, including fatal cases, have been reported with the use of nucleoside analogues alone or in combination with antiretrovirals. - Severe acute exacerbations of hepatitis B have been reported in patients who have discontinued anti-hepatitis B therapy, including telbivudine. Hepatic function should be monitored closely with both clinical and laboratory follow-up for at least several months in patients who discontinue anti-hepatitis B therapy. If appropriate, resumption of anti-hepatitis B therapy may be warranted. - Cases of myopathy have been reported with telbivudine use several weeks to months after starting therapy. Myopathy has also been reported with some other drugs in this class. Physicians considering concomitant treatment with these or other agents associated with myopathy should weigh carefully the potential benefits and risks and should monitor and advise patients to report any signs or symptoms of unexplained muscle pain, tenderness or weakness, particularly during periods of upward dosage titration. Telbivudine therapy should be interrupted if myopathy is suspected, and discontinued if myopathy is diagnosed. - Because telbivudine is eliminated primarily by renal excretion, co-administration of telbivudine with drugs that affect renal function may alter plasma concentrations of telbivudine and/or the coadministered drug. Dose interval adjustment is recommended in patients with reatinine clearance <50mL/min. - The safety and efficacy of telbivudine in liver transplant recipients are unknown. If telbivudine treatment is determined to be necessary for a liver transplant recipient who has received or is receiving an immunosuppressant that may affect renal function, such as cyclosporine or tacrolimus, renal function should be monitored both before and during treatment with telbivudine. - Patients should be advised that treatment with telbivudine has not been shown to reduce the risk of transmission of HBV to others through sexual contact or blood contamination. - Safety and effectiveness of telbivudine in pediatric patients under the age of 16 years have not been established. - Frequently occurring adverse events (>5%) in clinical studies were upper respiratory tract infection (14%), fatigue and malaise (12%), abdominal pain (12%), nasopharyngitis (11%), headache (11%), blood CPK increased (9%), cough (7%), nausea and vomiting (7%), influenza and influenza-like symptoms (7%), post-procedural pain (7%), diarrhea and loose stools (7%), and pharyngolaryngeal pain (5%). - Creatine kinase (CK) elevations were more frequent among subjects on telbivudine treatment. Grade 3/4 CK elevations occurred in 9% of telbivudine-treated patients and 3% of lamivudine-treated patients. - The optimal duration of treatment with TYZEKA has not been established. The relationship of initial treatment response to outcomes such as hepatocellular carcinoma and decompensated cirrhosis are unknown. About Idenix

Idenix Pharmaceuticals, Inc., headquartered in Cambridge, Massachusetts, is a biopharmaceutical company engaged in the discovery, development and commercialization of drugs for the treatment of human viral and other infectious diseases. Idenix’s current focus is on the treatment of infections caused by hepatitis B virus, hepatitis C virus and human immunodeficiency virus (HIV). For further information about Idenix, please refer to http://www.idenix.com.

Forward-looking Statements

This press release contains “forward-looking statements” within the meaning of The Private Securities Litigation Reform Act of 1995. Such forward- looking statements may be identified by implied discussions regarding clinical trial development of telbivudine or valopicitabine, any potential therapeutic benefits of telbivudine or valopicitabine or our clinical development programs in hepatitis B or C, or any potential pipeline candidates. 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. There can be no guarantees that Idenix will successfully advance any clinical product candidate or other component of our potential pipeline. In particular, management’s expectations could be affected by the unexpected regulatory actions or delays; uncertainties relating to results of clinical trials, including additional data relating to the ongoing clinical trials evaluating its product candidates; the company’s ability to obtain additional funding required to conduct its research, development and commercialization activities; the company’s dependence on its collaboration with Novartis Pharma AG; the ability of the company to attract and retain qualified personnel; competition in general; and the company’s ability to obtain, maintain and enforce patent and other intellectual property protection for its other product candidates and its discoveries. These and other risks which may impact management’s expectations are described in greater detail under the caption “Risk Factors” in the company’s quarterly report on Form 10-Q for the quarter ended September 30, 2006 and filed with the Securities and Exchange Commission and other filings that the company makes with the Securities and Exchange Commission.

All forward-looking statements reflect the company’s expectations only as of the date of this release 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. Idenix anticipates that subsequent events and developments may cause these views, expectations and beliefs to change. However, while Idenix may elect to update these forward-looking statements at some point in the future, it specifically disclaims any obligation to do so.

Idenix Pharmaceuticals’ Contacts:

Media: Teri Dahlman (617) 995-9905

Investors: Amy Sullivan (617) 995-9838

Idenix Pharmaceuticals, Inc.

CONTACT: Media, Teri Dahlman, +1-617-995-9905; Investors, Amy Sullivan+1-617-995-9838, both of Idenix Pharmaceuticals

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