A pharmaceutical firm has said almost all patients taking two of its experimental hepatitis C drugs appeared to have eliminated the virus after up to 12 weeks of treatment.

The patients took a fixed-dose combination of the drugs in a small mid-stage study for Gilead Sciences.

The data could help Gilead remain in the lead among drugmakers racing to develop better medicines for the potentially dangerous condition that also require far shorter durations of treatment.

Based on the favourable interim data from the trial of 60 previously untreated patients, named LONESTAR, Gilead said it plans to conduct a third late-stage study of the once-daily fixed-dose combination tablet.

It pairs the drugs sofosbuvir and ledipasvir.

The new Phase III trial, called ION-3, will enroll 600 patients new to treatment who have the most common genotype 1 form of hepatitis C, Gilead said.

It will evaluate the combination tablet for eight weeks of treatment, with and without another oral antiviral drug called ribavirin that is a mainstay of current standard treatments.

The trial will also test the combination drug for 12 weeks, without ribavirin.

Gilead said all 19 patients in the LONESTAR trial who took the combo pill for 12 weeks had a sustained virologic response (SVR), meaning they had no detectable signs of the virus, as assessed by blood tests given four weeks after completing therapy.

Moreover, the company said 40 of 41 patients who took the tablet for eight weeks were deemed free of the virus eight weeks after they completed treatment.

Gilead said one patient relapsed, and that patient was from a group that took the combo tablet but did not take ribavirin.

"We believe this data greatly strengthens Gilead's position in the hepatitis C market, with an all oral once-daily pill across all genotype 1 patients and potentially for only 8 weeks" of treatment, ISI Group analyst Mark Schoenebaum said in a research report.

Hepatitis C affects an estimated 170 million people worldwide, and if left untreated can lead to cirrhosis, liver cancer or the need for a new liver. Current treatments include use of interferon, an injectable drug that causes flu like symptoms.