Pharmasset and Roche Obtain FDA Consent to Start a Phase 2b Study With R7128 in Treatment...

Pharmasset and Roche Obtain FDA Consent to Start a Phase 2b Study With R7128
in Treatment Naive HCV Patients

PRINCETON, N.J., Jan. 12 /PRNewswire-FirstCall/ -- Pharmasset, Inc. (Nasdaq:
VRUS) announced today that they and their development partner, Roche, have
agreed with the FDA on the final design for a phase 2b trial with R7128, a
nucleoside inhibitor of hepatitis C (HCV), slated to initiate in the first
quarter of this year.

"We are pleased that R7128 is advancing into a large phase 2b trial," stated
Michelle Berrey, MD, MPH, Pharmasset's Chief Medical Officer. "R7128 is the
most advanced nucleoside polymerase inhibitor in development and we believe
this class of drug brings a number of advantages to HCV-infected patients.
R7128's higher barrier to resistance and activity across multiple viral
genotypes, as well as the promising short-term safety and tolerability, may
bring patients a new option for therapy. We look for this trial to better
define the optimal treatment duration with R7128 in combination with the
standard of care."

The phase 2b trial is anticipated to enroll about 400 treatment naive,
genotype-1 or genotype 4 HCV-infected patients. The trial will evaluate the
dose and duration of treatment of R7128 in combination with Pegasys(R) plus
Copegus(R). The primary efficacy endpoint of the trial will be the proportion
of patients that achieve a sustained virologic response (SVR), defined as
undetectable (measured by Roche TaqMan assay) HCV RNA 24 weeks after
completion of treatment. Patients will be enrolled into one of 5 arms:

-- 24 weeks of total treatment, with R7128 500mg bid in combination with
pegylated interferon and ribavirin for 12 weeks, followed by 12 weeks
of
pegylated interferon and ribavirin
-- 24 weeks of total treatment, with R7128 1000mg bid in combination with
pegylated interferon and ribavirin for 12 weeks, followed by 12 weeks
of
pegylated interferon and ribavirin
-- 24 weeks of total treatment, with R7128 1000mg bid in combination with
pegylated interferon and ribavirin for 8 weeks, followed by a further
16
weeks of pegylated interferon and ribavirin
-- 48 weeks of total treatment, with R7128 1000mg bid in combination with
pegylated interferon and ribavirin for 12 weeks, followed by a further
36 weeks of pegylated interferon and ribavirin.
-- A control arm with pegylated interferon and ribavirin for 48 weeks.

Patients in the 24 week arms will discontinue treatment at week 24 if they
achieved a rapid virological response (RVR), defined as undetectable level of
HCV RNA at week 4 ("RVR-guided"). Patients that do not achieve an RVR will
continue on the standard of care until week 48.

According to the current study design, patients will be enrolled as two
cohorts, with randomization of the second larger cohort being initiated based
on 12 week safety data of the first cohort.

During 2009, we expect to provide updates on the progress of the trial.

About R7128
R7128 is being developed for the treatment of chronic HCV infection. R7128 is
a prodrug of PSI-6130, a cytidine 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. R7128 has shown in vitro activity against all of the most common HCV
genotypes (1, 2, 3 and 4).

In a 4-week Phase 1 combination study that was conducted in 81 treatment-naive
patients chronically infected with HCV genotype 1, R7128 demonstrated
significant short-term antiviral activity with safety and tolerability
comparable to placebo with SOC. Results from the 500mg, 1500mg and 1000mg dose
cohorts (cohorts 1, 2 and 3) in 81 treatment-naive patients infected with HCV
genotype 1 indicated:

-- Results with R7128 500mg bid, 1000mg bid and 1500mg bid with SOC
achieved a mean 3.8 log10 IU/mL (30% RVR, 6 of 20), 5.0 log10 IU/mL
(88%
RVR, 22 of 25) and 5.1 log10 IU/mL (85% RVR, 17 of 20) decrease in
HCV
RNA, respectively. Results with placebo with SOC indicated patients
achieved a mean 2.9 log10 IU/mL decrease in HCV RNA and 18.75% (3 of
16)
patients achieved RVR (<15 IU/ml).

In a harder to treat, non-responder, genotype 2 and 3 HCV patient population
treated for 4 weeks:

-- Results with R7128 1500mg bid with SOC led to 90% of patients
achieving
an RVR (<15 IU/ml) compared to 60% in the standard of care arm.

In November 2008, Pharmasset, Roche and InterMune initiated the INFORM-1 trial
to investigate the combination of R7128 with InterMune's R7227 (ITMN-191), a
protease inhibitor in HCV patients in the absence of pegylated interferon and
ribavirin. Patients will receive a maximum of 14 days of combination
treatment, followed by Pegasys(R) plus Copegus(R) for a further 46 weeks. The
aim of the study is to investigate the safety and antiviral activity of the
combination.

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, has completed a 4-week clinical trial in
combination with Pegasys(R) plus Copegus(R) 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.

Contact
Richard E. T. Smith, Ph.D.
VP, Investor Relations and Corporate Communications
richard.smith@pharmasset.com
Office: +1 (609) 613-4181

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 adverse
events could cause the cessation or delay of any of the ongoing or planned
clinical trials and/or our development of our product candidates, the risk
that the results of previously conducted studies involving our product
candidates will not be repeated or observed in ongoing or future studies
involving 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, 2008 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.

SOURCE Pharmasset, Inc.

Richard E. T. Smith, Ph.D., VP, Investor Relations and Corporate
Communications of Pharmasset, Inc., +1-609-613-4181,
richard.smith@pharmasset.com