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Pharmasset Announces Intent To Amend QUANTUM Trial

PRINCETON, N.J., Dec. 16, 2011 /PRNewswire/ – Pharmasset, Inc. (NASDAQ:VRUS) announced today that the company will amend the design of the QUANTUM Phase 2b trial of the guanine nucleotide analog PSI-938 and discontinue all treatment arms with a regimen containing PSI-938. There are 235 individuals with hepatitis C virus (HCV) in the study who are receiving treatment with PSI-938 alone or in combination with PSI-7977 or PSI-7977 and ribavirin. During routine safety monitoring, the company detected laboratory abnormalities associated with liver function in subjects receiving PSI-938 300 mg once daily. These laboratory abnormalities have not been observed in patients receiving PSI-7977 and ribavirin in the QUANTUM study or in other trials evaluating PSI-7977. Both the 12 and 24-week PSI-7977 and ribavirin arms will continue unchanged, data from which will support NEUTRINO, an interferon free, 12-week Phase 3 study of PSI-7977 and ribavirin in patients with HCV genotype 1 (GT-1).

The subject of today’s announcement does not trigger the “key product event” clause set forth in section 4.1(t) of the Agreement and Plan of Merger entered into by Pharmasset and Gilead Sciences, Inc. on November 21, 2011 and does not alter either party’s rights and obligations under the terms of the agreement. Pharmasset anticipates that the transaction announced on November 21, 2011 will conclude in the first quarter of 2012.