Pharmasset Initiates Phase 2b ATOMIC Trial of PSI-7977 for Multiple HCV Genotypes

PRINCETON, N.J., March 30, 2011 /PRNewswire/ — Pharmasset, Inc.
(Nasdaq:
VRUS) announced today that screening has begun in a Phase 2b
study of PSI-7977, a nucleotide analog polymerase inhibitor for the
treatment of chronic hepatitis C (HCV). The trial will evaluate
PSI-7977 400mg QD with pegylated interferon and ribavirin in
patients with HCV genotype 1, 4, 5 or 6 who have not been treated
previously.

“We are encouraged by the early efficacy and safety data being
generated with our nucleotide analogs, PSI-7977 and PSI-938,”
stated Michelle Berrey, MD, MPH, Pharmasset’s Chief Medical
Officer.  “The ATOMIC trial is designed to explore 12 and 24
week durations of PSI-7977. The potency, high barrier to
resistance, and consistent antiviral activity across genotypes
provided the data to support an interferon free dosing period in
this trial, as well as enabling us to enroll multiple genotypes in
this trial.”  

About the Phase 2b ATOMIC Trial

This Phase 2b trial is planned to enroll approximately 300
patients with chronic HCV genotype 1 who have not been treated
previously. The primary endpoint of the trial will be the safety
and tolerability of PSI-7977 in combination with peginterferon and
ribavirin over 12 or 24 weeks. The trial will be conducted in the
U.S. Patients will be randomized (1:2:3) into the following
arms:

• PSI-7977 400mg QD with peginterferon and ribavirin for 12
  weeks;
• PSI-7977 400mg QD with peginterferon and ribavirin for 24
  weeks;
• PSI-7977 400mg QD with peginterferon and ribavirin for 12
  weeks, followed by either PSI-7977 400mg QD monotherapy for 12
  weeks or PSI-7977 400mg QD plus ribavirin for 12 weeks.

HCV GT1 patients will be stratified by IL28B status and baseline
HCV RNA to ensure balance across cohorts. An additional 25
treatment-naïve patients w

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