SIX-MONTH PHASE IIB DATA OF TELBIVUDINE (LDT) FOR THE TREATMENT OF HEPATITIS B

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FOR IMMEDIATE RELEASE
Contact:
Idenix Pharmaceuticals, Inc.
(617) 250-3119
Teri Babine
Idenix Public Relations Noonan/Russo Presence Euro RSCG
(212) 845-4200
Amy Garay (investor) ext. 4261
Lynn Blenkhorn (media) ext. 4276


IDENIX PHARMACEUTICALS PRESENTS SIX-MONTH PHASE IIB DATA OF TELBIVUDINE (LDT) FOR THE TREATMENT OF HEPATITIS B INFECTION

- Clinical data demonstrating marked antiviral activity presented at the Annual Meeting of the American Association for the Study of Liver Diseases (AASLD) -

Boston, MA, November 5, 2002 - Idenix Pharmaceuticals, Inc. announced yesterday interim 24-week data from an ongoing international phase IIb clinical trial of telbivudine (LdT), the Company's lead drug candidate for the treatment of chronic hepatitis B virus (HBV) infection. This clinical trial compares telbivudine therapy with lamivudine, the current standard of care, and with the combination of telbivudine plus lamivudine.

The interim study results indicate a strong antiviral response coupled with substantial improvement in ALT level (a serum marker of liver disease) in patients receiving telbivudine, either alone or in combination with lamivudine. The median reduction in serum virus load for all LdT-containing arms was greater than 6 log10 or a million fold. In patients receiving lamivudine alone, a median reduction of 4.67 log10 occurred. To date, LdT treatment appears to have been well tolerated by patients and no treatment-limiting or dose-related adverse events have been observed.

"Results from this study confirm the safety profile and potent viral suppression we have seen in previous clinical trials of LdT," said Ching-Lung Lai, M.D., Professor of Medicine at the University of Hong Kong and a principal study investigator who presented the new data at the annual conference of the American Association for the Study of Liver Diseases (AASLD). "Among patients receiving an LdT-containing treatment, greater viral suppression has been achieved during the 24 weeks of treatment than in previous shorter duration studies. We look forward to evaluating the effects of longer treatment in the final 48-week data."

Study Description
Telbivudine is a nucleoside that exhibits marked and selective activity against HBV replication in laboratory assays. The randomized, blinded, international multicenter phase IIb clinical trial is comparing the safety and antiviral effectiveness of telbivudine, and telbivudine in combination with lamivudine, to a control arm of lamivudine alone. The study enrolled 104 adults with chronic hepatitis B and an average age of 37 years (range: 16-68 years). The trial is being conducted at 19 sites in Hong Kong, Singapore, France, Canada and the United States. The study includes five treatment arms as follows: telbivudine 400 mg, telbivudine 600 mg, telbivudine 400 mg + lamivudine 100 mg, telbivudine 600 mg + lamivudine 100 mg and lamivudine 100 mg. At baseline, patients had a median serum HBV DNA of 9.28 log10. All patients are to be dosed orally once daily for a treatment period of one year. Treatment groups are well matched for demographic and disease features.

Study Results
In the five treatment groups, median reductions in viral load (serum HBV DNA) after 24 weeks are as follows: 6.08 log10 for telbivudine 400 mg; 6.11 log10 for telbivudine 600 mg; 6.21 log10 for telbivudine 400 mg + lamivudine; 6.24 log10 for telbivudine 600 mg + lamivudine; and 4.67 log10 for lamivudine alone.

After 24 weeks of treatment, 92% of patients receiving an LdT-containing regimen had achieved suppression of viral load below 5 log10, a level associated with clinical improvements in liver disease according to the hepatitis B Practice Guidelines published by the AASLD 1. Among patients receiving lamivudine alone, 63% of such patients achieved suppression of viral load below 5 log10. Further, a significant proportion of patients on LdT treatment achieved reductions in viral levels below the limit of detection of a highly sensitive polymerase chain reaction (PCR) assay. Patients achieving undetectable virus levels at week 24 of the study accounted for 32% of patients receiving LdT monotherapy, 32% of patients receiving LdT in combination with lamivudine and 16% of patients receiving lamivudine monotherapy.

Study results also show that a high proportion of LdT-treated patients achieved early normalization of serum ALT. Among patients receiving LdT monotherapy, 49% demonstrated normalized ALT levels within 12 weeks of treatment, which increased to 75% by 24 weeks.

This interim 24-week data supports the strong safety profile demonstrated in previous studies of LdT. With all patients reaching 24 weeks of treatment, there have been no serious treatment-related adverse events (AE), no discontinuations for AEs and no dose-related AEs or laboratory abnormalities.

"These interim results of the phase IIb study support our plans for a large phase III clinical trial of telbivudine, which will be conducted globally in North America, Europe and Asia," commented Nathaniel Brown, M.D., Idenix's Senior Vice President of Hepatitis Clinical Research. "We hope that the safety profile and antiviral activity demonstrated thus far for LdT will translate into long-term clinical benefits for hepatitis B patients."

There are approximately 350 million people worldwide with chronic hepatitis B virus infection, of whom approximately 33% have potentially progressive and life-threatening liver disease associated with their chronic HBV infection. Chronic hepatitis B can lead to cirrhosis, liver failure and hepatocellular carcinoma (liver cancer). Globally, hepatitis B accounts for over one million deaths annually, making it the ninth leading cause of death worldwide.

About Idenix:
Idenix Pharmaceuticals, Inc., formerly Novirio Pharmaceuticals Limited, is a biopharmaceutical company engaged in the discovery and development 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). Idenix is developing telbivudine in collaboration with Sumitomo Pharmaceuticals Co. Ltd. for Japan and selected Asian markets.