Gilead Sciences Inc said its experimental combination treatment was effective against all forms of hepatitis C infection, citing data from four late-stage studies.

The trials were evaluating a once-daily, fixed-dose combination of the drugmaker's hep C drug, Sovaldi, with velpatasvir, an experimental NS5A inhibitor.

The main goal of each study was to achieve a cure, or sustained virological response, 12 weeks after the completion of therapy.

The combination is Gilead's second single-tablet treatment for hep C. Harvoni, its other treatment, is already approved for genotype 1 infections.

Sovaldi and Harvoni brought in combined sales of about $4.9 billion last quarter.

The U.S. Food and Drug Administration has granted the experimental combination "breakthrough therapy" status, expediting the development and review of the drug.

Gilead expects to file marketing applications for the combination - which could eliminate the need for HCV genotype testing altogether - by the fourth quarter, it said on Monday.