Pharmasset to Present New Data on RG7128 and PSI-7977 at the EASL Conference

Pharmasset to Present New Data on RG7128 and PSI-7977 at the EASL Conference

-- Follow up data from a 28 day trial with RG7128 and standard of care demonstrated an SVR of 65% in HCV genotype 2/3 prior non-responders -- In vitro results demonstrate that a combination of two nucleotide analogs, PSI-7977 and PSI-938, are able to suppress S282T-resistant replicons

PRINCETON, N.J., April 13, 2010 /PRNewswire via COMTEX News Network/ -- Pharmasset, Inc. (Nasdaq: VRUS) announces the oral presentation of new sustained virologic response (SVR) follow-up data in hepatitis C virus (HCV) genotype 2 and 3 non-responder patients treated for 28 days with RG7128 in combination with the standard of care (SOC), Pegasys(R) and Copegus(R), and presentation of an&nb sp;in vitro combination study with PSI-7977 and PSI-938. Both presentations are at the 45th Annual Meeting of the European Association for the Study of the Liver (EASL) in Vienna, Austria (April 14-18, 2010).

On April 15, Edward Gane, M.D., Associate Professor, University of Auckland, and Director, Auckland Clinical Studies Limited, will give an oral presentation entitled "Sustained virologic response (SVR) following RG7128 1500mg BID/PegIFN/RBV for 28 days in HCV Genotype 2/3 prior non-responders" at 5 PM CEST during the hepatitis C drug development session. Data from this trial suggest that the nucleoside RG7128 in combination with SOC is effective in retreatment of HCV genotype 2/3 relapsers/nonresponders and may provide an attractive option for treatment of prior non-responders and treatment-naive patients with HCV genotype 2/3. Larger studies are required to confirm these findings, determine the optimal duration of RG7128 therapy, and evaluate utility in treatment-naive genotype 2/3 patients.

On April 17, Dr Vero nique Zennou, a Pharmasset scientist, will present a poster entitled "Combination of two complementary nucleotide analogues PSI-7977 and PSI-938 effectively clears wild type and NS5B S282T HCV replicons - comparison with combinations of other antiviral compounds" (Poster 1034). The data indicate that in vitro combinations of two nucleotides targeting NS5b effectively suppress resistant replicons with no emergence of resistance. The poster will include comparative data on combinations of other direct acting antivirals (DAA) targeting different HCV proteins.

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 C virus (HCV) and, secondarily, on the development of Racivir(TM) for the treatment of human immunodeficiency virus (HIV). Our research and development efforts focus on nucleoside/tide analogs, a class of compounds which act as alternative substrates for the viral polymerase, thus inhibiting viral replication. We currently have three clinical-stage product candidates. RG7128, a nucleoside analog for chronic HCV infection, is in two Phase 2b clinical trials in combination with Pegasys(R) and Copegus(R) and is also in the INFORM studies, the first series of studies designed to assess the potential of combinations of small molecules without Pegasys(R) and Copegus(R) to treat chronic HCV. These clinical studies are being conducted through a strategic collaboration with Roche. Our other clinical stage candidates include PSI-7977, an unpartnered, next- generation HCV nucleotide analog that is in a Phase 2a trial; PSI-938 in Phase 1a and Racivir, for the treatment of HIV, which has completed a Phase 2 clinical trial. We also have in our pipeline an additional purine nucleotide analog, PSI-661, an isom er of PSI-879, in advanced preclinical development.

Pegasys(R) and Copegus(R) are registered trademarks of Roche.

Contact
Richard E. T. Smith, Ph.D.
VP, Investor Relations and Corporate Communications
Office: +1 (609) 613-4181


Forward-Looking Statements

Pharmasset "Safe Harbor" Statement under the Private Securities Litigation Reform Act of 1995: Statements in this press release regarding our business that are not historical facts are "forward-looking statements" that involve risks and uncertainties, including, without limitation, the risk that adverse events could cause the cessation or delay of any of the ongoing or planned clinical trials and/or our development of our product candidates, the risk that the results of previously conducted studies involving our product candidates will not be repeated or observed in ongoing or future studies involving our product candidates, the risk that our collaboration with Roche will not continue or will not be successful, and the risk that any one or more of our product candidates will not be successfully developed and commercialized. For a discussion of these and other risks and uncertainties, any of which could cause our actual r esults to differ from those contained in the forward-looking statements, see the section of our Annual Report on Form 10-K for the fiscal year ended September 30, 2009 and our Quarterly Report on Form 10-Q for the period ended December 31, 2009 filed with the Securities and Exchange Commission entitled "Risk Factors" and discussions of potential risks and uncertainties in our subsequent filings with the Securities and Exchange Commission.

SOURCE Pharmasset, Inc.