Pharmasset Reports Positive Preliminary Antiviral Data With PSI-7851 for the Treatment of H...(-0.03 -------------------------------...),Health

PSI-7851 demonstrated potent antiviral activity with a mean HCV RNA decrease of -0.49 log(10) IU/mL, -0.61 log(10) IU/mL and -1.01 log(10) IU/mL in patients receiving 50mg QD, 100mg QD, and 200mg QD, respectively.

PSI-7851 Pharmacokinetic and Safety Summary

Pharmacokinetics were similar between healthy subjects in the single ascending dose study and HCV infected patients in the multiple ascending dose study. PSI-7851 was generally safe and well tolerated across all cohorts with no discontinuations. There were no serious adverse events and no dose-related trends in adverse events or laboratory abnormalities.

"We are very encouraged by the preliminary efficacy and safety data with PSI-7851, our second generation nucleotide analog," said Michelle Berrey, MD, MPH, Pharmasset's Chief Medical Officer. "The data from these first three cohorts demonstrate that we have achieved our goal of identifying a nucleotide analog with good efficacy that can be administered once daily at a low milligram dose. Given these characteristics and the potential benefits of nucleotide analogs over other classes of HCV direct acting antivirals, we continue to believe that PSI-7851 could become a key component of any future combination treatment regimen for HCV."

Conference Call and Webcast

Members of Pharmasset's management team will host a conference call today, Friday, July 31, 2009, at 8:00 a.m. ET to discuss the preliminary results of the multiple ascending dose trial with PSI-7851. Investors may listen to the webcast of the conference call live on the "Events & Presentations" section of Pharmasset's website, www.pharmasset.com. Alternatively, investors may listen to the call by dialing (888) 806-6208 from locations in
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