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Roche and Pharmasset To Present the R7128 Monotherapy Resistance Profile

-- Study concludes there was no evidence of the development of viral resistance to R7128 after 2 weeks of monotherapy in hepatitis C patients --

PRINCETON, N.J., February 6, 2008 /PRNewswire-FirstCall/ -- Pharmasset and Roche will present the R7128 monotherapy resistance profile at the EASL-AASLD-APASL-ALEH-IASL Conference on Hepatitis B & C Virus Resistance to Antiviral Therapies being held in Paris, France from February 14-16, 2008. The scientific abstract for poster board no. 36, entitled "Lack of Viral Resistance after 14-day Monotherapy Treatment with R7128 in Treatment-experienced Patients Infected with HCV Genotype 1," is currently available on the conference website at http://www.easl.ch/hepatitis-conference/program/session1.asp. The poster presentation will be available for download in PDF format after it is presented on February 14, 2008 in the "Events & Presentations" section of Pharmasset's website at http://investor.pharmasset.com/events.cfm.

About R7128

R7128 is being developed for the treatment of chronic HCV infection through Pharmasset's collaboration with Roche. R7128 is a prodrug of PSI-6130, a nucleoside analog inhibitor of HCV RNA polymerase. A prodrug is a chemically modified form of a molecule designed to enhance the absorption, distribution and metabolic properties of that molecule.

In a Phase 1 clinical trial, R7128 demonstrated potent, dose-dependent antiviral activity across four patient cohorts (n=40) receiving 750mg or 1500mg administered either once-daily or twice-daily for 2 weeks as monotherapy. The greatest mean decrease in HCV RNA from baseline was observed in the patient cohort that received 1500mg twice-daily, the highest dose of R7128 administered in the study. These patients experienced a mean 2.7 log10 IU/mL (>99%) decrease in HCV RNA. There was no evidence of the selection of PSI-6130 resistant virus in any dose cohort during the 2 weeks of dosing.

The preliminary results of a 4 week Phase 1 clinical trial to evaluate two oral dose levels of R7128 in combination with Pegasys(R) (pegylated interferon) plus Copegus(R) (ribavirin) in 50 treatment-naive patients chronically infected with HCV genotype 1 demonstrated potent short-term antiviral activity. Eighty-five (85%) of patients receiving R7128 1500mg and Pegasys plus Copegus (n=20) achieved undetectable HCV RNA levels following 4 weeks of treatment, or rapid virologic response. The R7128 combination cohorts demonstrated safety and tolerability comparable to placebo with Pegasys plus Copegus.

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).

Pharmasset is currently developing three product candidates. Clevudine, for the treatment of chronic HBV infection, is enrolling Phase 3 clinical trials for registration in North, Central and South America and Europe. Clevudine is already approved for HBV in South Korea and marketed by Bukwang Pharmaceuticals in South Korea under the brand name Levovir. R7128, an oral treatment for chronic HCV infection, is in a 4-week Phase 1 clinical trial in combination with Pegasys plus Copegus through a strategic collaboration with Roche. Racivir, which is being developed for the treatment of HIV in combination with other approved HIV drugs, has completed a Phase 2 clinical trial.

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

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 we will fail to present the monotherapy resistance profile of R7128, the risk that we will fail to release final safety and efficacy data from a Phase 1, Part 3 combination study of R7128 with Pegasys plus Copegus or that such final data will not corroborate our preliminary results, the risk that adverse events could cause the cessation of clinical studies and/or the development of any of 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 risks and uncertainties, any of which could cause our actual results 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, 2007 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.

    Contact

    Alan Roemer, Vice President

    Investor Relations & Corporate Communications

    

    Office: (609) 613-4125

alan.roemer@pharmasset.com

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

Web site: http://www.pharmasset.com/

Ticker Symbol: (NASDAQ-NMS:VRUS)

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Posted: February 2008

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