(Adds details on other studies, analyst comment, background)
April 19 (Reuters) - An experimental hepatitis C drug acquired by Gilead Sciences Inc when it paid nearly $11 billion to buy Pharmasset has produced encouraging results in a closely-watched clinical trial, results of which were released in Barcelona.
The U.S. company said that of 25 patients with genotype 1 hepatitis who completed 12 weeks of treatment with a combination of GS-7977 and the older antiviral ribavirin (RBV), 88 percent still had undetectable levels of virus four weeks after completion of treatment.
Three patients in the study, known as ELECTRON, experienced viral relapse.
A second study, QUANTUM, which contained more difficult to treat patients, produced less impressive results, with 59 percent of patients having undetectable virus levels.
Mark Schoenebaum, an analyst at ISI Group, said the ELECTRON data was better than expected, since most analysts had expected a result around 50 percent, while the QUANTUM result was about in-line with expectations.
The market for treating hepatitis C has burgeoned in the last year with two new breakthrough treatments approved for sale in the United States and the promise of even better medicines in the pipeline, like the Gilead drug GS-7977.
GS-7977 works by blocking an enzyme essential to the replication of the hepatitis C virus. It is one of a new class of treatments designed to be given without interferon, which helps boost the body's immune system but can also cause debilitating, flu-like symptoms.
Vertex Pharmaceuticals Inc's new hepatitis C drug Incivek and Merck & Co's Victrelis both won U.S. approval last year. (Reporting by Ben Hirschler; Editing by Mark Potter)