Pharmasset, Inc. Announces Clevudine and Hepatitis C Presentations at EASL

PRINCETON, N.J., April 3 /PRNewswire/ -- Pharmasset announced today that presentations of preclinical studies of Clevudine for the treatment of hepatitis B (HBV) and PSI-6130, the parent molecule of R7128, for the treatment of hepatitis C (HCV) will be made during the 42nd Annual Meeting of the European Association for the Study of the Liver (EASL) being held in Barcelona, Spain from April 11-15, 2007. The PSI-6130 studies were conducted through Pharmasset’s HCV collaboration with Roche. Dr. Phillip Furman, Pharmasset’s Vice President of Biological Sciences, will be presenting Pharmasset’s posters beginning on Thursday, April 12, 2007 at 7:00pm (CEST). The complete abstracts can be viewed at http://www.easl.ch/liver-meeting.

Clevudine is Efficiently Phosphorylated to the Active Triphosphate form in Human Hepatocytes

C. Niu 1, E. Murakami 1, M.J. Otto 1, P.A. Furman 1 1 Pharmasset, Inc., Princeton, NJ, USA Study subject: initial half-life of the clevudine triphosphate.

Inhibition of HCV Replication by PSI-6130: Characterization of Activity in the HCV Replicon System

W.R. Jiang 1, S. Ali 1, S. Le Pogam 1, C. Daniel 1, S. Chiu 1, T. Kretz 1, I. Najera 1, P. Furman 2, N. Cammack 1, J. Symons 1

1 Roche Palo Alto LLC, Palo Alto, CA, USA; 2 Pharmasset Inc., Princeton, NJ, USA

Study subject: inhibition of HCV replication using combinations of PSI- 6130 with other HCV inhibitors.

Inhibition of HCV Replication by PSI-6130: Mechanism of Biochemical Activation and Inhibition

P.A. Furman 1, E. Murakami 1, H. Bao 1, J. Symons 2, M.J. Otto 1

1 Pharmasset, Inc., Princeton, NJ, USA; 2 Roche Palo Alto LLC, Palo Alto, CA, USA

Study subject: investigation of the enzymes involved in the phosphorylation of PSI-6130 and inhibition of HCV NS5B.

About Clevudine

Clevudine is an oral, once-daily pyrimidine nucleoside analog that we are developing for the treatment of HBV. We licensed clevudine from Bukwang Pharm. Co., Ltd., a Korean pharmaceutical company. Bukwang has recently initiated the commercial launch of clevudine in the Korean market under the brand name Levovir. We plan to initiate two Phase 3 clinical trials of clevudine for registration in the United States and Europe in the second calendar quarter of 2007.

About R7128, a Prodrug of PSI-6130

R7128 is a polymerase inhibitor being developed for the treatment of chronic hepatitis C. R7128 is a prodrug of PSI-6130, a pyrimidine nucleoside analog inhibitor of HCV RNA polymerase. The current R7128 Phase I clinical trial is a multiple center, observer-blinded, randomized and placebo- controlled study to investigate the pharmacokinetics, pharmacodynamics, safety, tolerability and food effect of R7128 in healthy volunteers and in patients chronically infected with HCV genotype 1.

About Hepatitis B Virus (HBV)

Hepatitis B viruses can cause liver disease leading to significant morbidity and death. HBV can cause either acute or chronic (lifelong) infection. The World Health Organization (WHO) has reported that approximately 350 million people worldwide have chronic HBV infection. According to the Centers for Disease Control and Prevention (CDC), approximately 1.25 million people in the United States are chronically infected with HBV, and the Hepatitis B Foundation reports that 100,000 people will become infected with HBV this year.

About Hepatitis C Virus (HCV)

Hepatitis C is a blood-borne infectious disease of the liver and is a leading cause of chronic liver disease and liver transplants. The WHO estimates that nearly 180 million people worldwide are infected with hepatitis C virus (HCV). The CDC has reported that almost four million people in the United States have been infected with HCV, of whom 2.7 million are chronically infected.

About Pharmasset

Pharmasset is a clinical-stage pharmaceutical company committed to discovering, developing and commercializing novel drugs to treat viral infections. Pharmasset’s primary focus is on the development of oral therapeutics for the treatment of hepatitis B virus (HBV), hepatitis C virus (HCV) and human immunodeficiency virus (HIV).

Contact: Alan Roemer Vice President, Investor Relations & Corporate Communications alan.roemer@pharmasset.com Office: (609) 613-4125

STATEMENTS IN THIS COMPANY PRESS RELEASE MAY CONSTITUTE FORWARD-LOOKING STATEMENTS AND ARE SUBJECT TO NUMEROUS RISKS AND UNCERTAINTIES, INCLUDING THE FAILURE OF CLEVUDINE AND R7128 TO PERFORM AS EXPECTED, THE COMPANY’S ABILITY TO ATTRACT AND RETAIN QUALIFIED PERSONNEL TO CONDUCT THE REQUIRED CLINICAL TRIALS OF CLEVUDINE AND R7128 , THE STATUS OF THE COMPANY’S HCV COLLABORATION WITH ROCHE, THE COMPANY’S FUTURE CAPITAL NEEDS TO FUND THE CLEVUDINE AND R7128 DEVELOPMENT PROGRAMS, THE COMPANY’S ABILITY TO OBTAIN ADDITIONAL FINANCING, THE COMPANY’S ABILITY TO OBTAIN REQUIRED REGULATORY APPROVALS FOR CLEVUDINE AND R7128, THE DEVELOPMENT OF COMPETITIVE HBV AND HCV PRODUCTS BY OTHERS, THE EXISTENCE OF THIRD-PARTY PATENT RIGHTS, AND OTHER RISKS INHERENT IN DISCOVERY AND DEVELOPMENT STAGE PROGRAMS AT A BIOTECHNOLOGY COMPANY. THE ACTUAL RESULTS FOR CLEVUDINE AND R7128 MAY DIFFER MATERIALLY FROM THOSE ANTICIPATED IN THIS COMPANY PRESS RELEASE. THE COMPANY DISCLAIMS ANY OBLIGATION TO UPDATE THE STATEMENTS CONTAINED IN THIS COMPANY PRESS RELEASE.

Pharmasset, Inc.

CONTACT: Alan Roemer, Vice President, Investor Relations & CorporateCommunications of Pharmasset, Inc., +1-609-613-4125,alan.roemer@pharmasset.com

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