Roche and Pharmasset To Present the R7128 Monotherapy Resistance Profile

Thursday, February 7, 2008 General News
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PRINCETON, N.J., Feb. 6 Pharmasset(Nasdaq: VRUS) and Roche will present the R7128 monotherapy resistance profileat the EASL-AASLD-APASL-ALEH-IASL Conference on Hepatitis B & C VirusResistance to Antiviral Therapies being held in Paris, France from February14-16, 2008. The scientific abstract for poster board no. 36, entitled "Lackof Viral Resistance after 14-day Monotherapy Treatment with R7128 inTreatment-experienced Patients Infected with HCV Genotype 1," is currentlyavailable on the conference website at The posterpresentation will be available for download in PDF format after it ispresented on February 14, 2008 in the "Events & Presentations" section ofPharmasset's website at

About R7128

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

In a Phase 1 clinical trial, R7128 demonstrated potent, dose-dependentantiviral activity across four patient cohorts (n=40) receiving 750mg or1500mg administered either once-daily or twice-daily for 2 weeks asmonotherapy. The greatest mean decrease in HCV RNA from baseline was observedin the patient cohort that received 1500mg twice-daily, the highest dose ofR7128 administered in the study. These patients experienced a mean 2.7 log10IU/mL (>99%) decrease in HCV RNA. There was no evidence of the selection ofPSI-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 twooral dose levels of R7128 in combination with Pegasys(R) (pegylatedinterferon) plus Copegus(R) (ribavirin) in 50 treatment-naive patientschronically infected with HCV genotype 1 demonstrated potent short-termantiviral activity. Eighty-five (85%) of patients receiving R7128 1500mg andPegasys plus Copegus (n=20) achieved undetectable HCV RNA levels following 4weeks of treatment, or rapid virologic response. The R7128 combinationcohorts demonstrated safety and tolerability comparable to placebo withPegasys plus Copegus.

About Pharmasset

Pharmasset is a clinical-stage pharmaceutical company committed todiscovering, developing and commercializing novel drugs to treat viralinfections. Pharmasset's primary focus is on the development of oraltherapeutics 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 clinicaltrials for registration in North, Central and South America and Europe.Clevudine is already approved for HBV in South Korea and marketed by BukwangPharmaceuticals in South Korea under the brand name Levovir. R7128, an oraltreatment for chronic HCV infection, is in a 4-week Phase 1 clinical trial incombination with Pegasys plus Copegus through a strategic collaboration withRoche. Racivir, which is being developed for the treatment of HIV incombination with other approved HIV drugs, has completed a Phase 2 clinicaltrial.

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

Forward-Looking Statements

Pharmasset "Safe Harbor" Statement under the Private Securities LitigationReform Act of 1995: Statements in this press release regarding our businessthat are not historical facts are "forward-looking statements" that involverisks and uncertainties, including without limitation the risk that we willfail to present the monotherapy resistance profile of R7128, the risk that wewill fail to release final safety and eff

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