Gilead Sciences' (NASDAQ:GILD) sofosbuvir has gone 4-for-4 in phase 3 trials treating hepatitis C patients.

The latest data come from a trial dubbed Fusion, which tested sofosbuvir plus a generic drug called ribavirin in patients infected with genotype 2 or 3 hepatitis C virus who failed prior treatment. Treating patients with sofosbuvir and ribavirin for 12 weeks left 50% of them free of the virus 12 weeks after treatment. Extending the treatment to 16 weeks increased the cure rate to 73%.

Historically, 25% of treatment-experienced patients infected with genotype 2 or 3 virus who were re-treated with the current standard of care would become virus-free. The difference between the observed treatment with sofosbuvir and the historical data was statistically significant.

The positive Fusion data follows data from three other positive phase 3 trials -- Positron, Fission, and Neutrino -- where sofosbuvir was tested in a variety of settings, including patients infected with viruses of all six genotypes, newly diagnosed patients, and in combination with the current standard of care.

Gilead plans to use the data from the four clinical trials to support applications for approval of sofosbuvir. The full data from the studies will be presented at an upcoming scientific conference.

Fool contributor Brian Orelli has no position in any stocks mentioned. The Motley Fool recommends Gilead Sciences. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.