Pharmasset Initiates Racivir(R) Phase II HIV Study

ATLANTA -- Pharmasset, Inc. has initiated a Phase II clinical study to assess the safety, tolerability, and antiviral effect of substituting Racivir (RCV) for Epivir(R) (lamivudine, 3TC) in treatment-experienced HIV-infected individuals. The goal of this study, RCV-201, is to evaluate HIV viral load reduction, particularly in individuals carrying the M184V mutation who are failing their current drug regimens.

"M184V is one of the most prevalent viral mutations resulting from both Epivir and Emtriva HIV therapies," noted Dr. Michael J. Otto, Pharmasset's executive vice president of Pharmaceutical Research. "If this study demonstrates that Racivir is more effective than Epivir in reducing the viral load of patients carrying virus strains with the M184V mutation, Racivir could become an alternative to Epivir in the treatment of drug-resistant HIV."

RCV-201, is a randomized, double-blind, placebo-controlled, multicenter study in the United States, Argentina, Mexico and Panama, designed to include 60 patients. The study entry criteria requires participants to have been receiving lamivudine as part of their antiretroviral therapy for the previous 60 days, to carry the M184V mutation, and to have an HIV RNA viral load of greater than or equal to 2,000 copies/mL. The study has a blinded treatment period of up to 28 days, followed by an open label treatment period of up to 20 weeks. Patients will be subsequently followed for an additional four weeks after the conclusion of the study treatment periods.

"Drug resistance continues to be a significant problem in HIV therapy," stated Schaefer Price, Pharmasset's president and CEO. "Pharmasset is committed to the development of HIV drugs that address emerging viral resistance."

Racivir is a nucleoside analog that is being developed at Pharmasset under a U.S. FDA IND for the treatment of HIV-1 and hepatitis B (HBV). A Phase I single-dose, oral pharmacokinetic study in healthy volunteers demonstrated that Racivir was safe and well-tolerated at all doses studied. In a Phase Ia/IIb 14-day study, plasma HIV RNA levels dropped two logs by day 14 in HIV-infected treatment-naïve patients receiving a triple drug combination of Racivir, Zerit(R) (D4T, stavudine), and Sustiva(R) (efavirenz).

   * Epivir is a registered trademark of GlaxoSmithKline.

     Emtriva is a registered trademark of Gilead Sciences.

     Zerit and Sustiva are registered trademarks of Bristol-Myers Squibb.

Source: Pharmasset, Inc.