Pharmasset Affirms Safety and Continued Progress in Clinical Development of RG7128

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Pharmasset Affirms Safety and Continued Progress in Clinical Development of

RG7128

From the PharmaLive.com News Archive - May. 04, 2010

- Responds to inaccuracies in PharmaWire article

PRINCETON, N.J., May 4 /PRNewswire-FirstCall/ -- Pharmasset, Inc. (NASDAQ: VRUS)

, in response to certain inaccuracies in an article published by PharmaWire on

May 3, 2010 about its development program for treatment of hepatitis C virus

(HCV) in collaboration with Hoffmann-La Roche Inc. and F. Hoffmann-La Roche Ltd,

stated today that the development of RG7128 is on track, and that no safety or

other concerns have delayed the program.

More specifically, M. Berrey, M.D., M.P.H., Chief Medical Officer,

stated, " In discussions with key colleagues at Roche, we have confirmed that the

clinical data available on RG7128 to date indicate no concern with the safety

profile of the compound. All safety data are reviewed by an independent data

monitoring committee (DMC) throughout the conduct of this ongoing Phase IIb

trial. While additional studies are necessary and appropriate to assess the

safety and efficacy of RG7128, there has been no indication of anemia, bone

marrow suppression, or nephrotoxicity, as inaccurately indicated in the

PharmaWire article. "

Based on the timeline of the PROPEL RG7128 study, almost all of the 408 patients

enrolled in the study have already completed their scheduled 8 or 12 weeks of

the triple combination portion of the assigned treatment (RG7128 plus standard

of care). The last patient enrolled in this study is to receive his or her last

dose of RG7128 or placebo in early May.

The development of RG7128 is not on hold or delayed and there are no plans to

amend any ongoing protocol to explore lower doses, in refutation of statements

in the PharmaWire article.

Lubetkin, Executive Vice President and General Counsel, said, " Pharmasset

is troubled that any news organization would issue an article rife with

unsupportable and false statements. One of the two named sources in the article

confirmed that his statements, which were in the context of an off-the-record

discussion about R1626, a Roche nucleoside on clinical hold, were inaccurately

reported and misinterpreted as applying to RG7128. The development efforts for

RG7128 are on track and ongoing. We sincerely hope that PharmaWire promptly

publishes a retraction of this misleading and false article. "

About Pharmasset

Pharmasset is a clinical-stage pharmaceutical company committed to discovering,

developing, and commercializing novel drugs to treat viral infections.

Pharmasset is focusing primarily on the development of oral therapeutics for the

treatment of hepatitis C virus (HCV) and secondarily on the development of

Racivir for the treatment of human immunodeficiency virus (HIV). Our

research and development efforts focus on nucleoside/tide analogs, a class of

compounds which act as alternative substrates for the viral polymerase, thus

inhibiting viral replication. We currently have four clinical-stage product

candidates. RG7128, a cytosine nucleoside analog for chronic HCV infection, is

in two Phase 2b clinical trials in combination with Pegasys® plus Copegus® and

is also in the INFORM studies, a series of studies designed to assess the

potential of combinations of two oral, direct acting antivirals without

pegylated interferon and ribavirin to treat chronic HCV. These clinical studies

are being conducted through a strategic collaboration with Roche. Our other,

unpartnered, clinical-stage candidates for the treatment of HCV include

PSI-7977, a uracil nucleotide analog that is in a Phase 2a trial, and PSI-938, a

guanine nucleotide analog that is in a Phase 1 trial. We also have in our

pipeline an additional guanine nucleotide analog, PSI-661, in advanced

preclinical development for the treatment of HCV. Racivir, for the treatment of

HIV, has completed a Phase 2 clinical trial.

Pegasys® and Copegus® are registered trademarks of Roche.

Contact

E. T. , Ph.D.

VP, Investor Relations and Corporate Communications

Office: +1 (609) 613-4181

Forward-Looking Statements

Statements in this press release regarding our business that are not historical

facts are " forward-looking statements " that involve risks, uncertainties and

other important factors, 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 and other risks, uncertainties and important factors, any of

which could cause our actual results to differ from those contained in the

forward-looking statements, see the section entitled " Risk Factors " in our

Annual Report on Form 10-K for the fiscal year ended September 30, 2009 and our

Quarterly Report on Form 10-Q for the period ended December 31, 2009 filed with

the Securities and Exchange Commission and discussions of potential risks,

uncertainties and other important factors in our subsequent filings with the

Securities and Exchange Commission.

Source: Pharmasset, Inc.

CONTACT: E. T. , Ph.D., VP, Investor Relations and

Corporate Communications, +1-609-613-4181

Web Site: http://www.pharmasset.com/