The first all-oral regimen for hepatitis C virus (HCV) infection has been endorsed by a US Food and Drug Administration advisory committee.

The panel has voted unanimously to approve Gilead Sciences' NS5B polymerase inhibitor sofosbuvir in combination with ribavirin to treat two less common forms of HCV - genotypes 2 and 3 - and also backed its use in combination with injectable interferon-based therapy and ribavirin for genotypes 1 and 4 in treatment-naïve patients.

The positive vote was widely anticipated as treatment of HCV moves inexorably towards combinations of new directly-acting agents that remove the need for interferon treatment, which as well as being injectable can have unpleasant side effects and is ineffective or unusable in up to half of all HCV cases.

Genotype 1 accounts for around 70% of all cases of HCV, with genotype 2 the next most common form and types 3 and 4 found in fairly limited geographies. Sofosbuvir is also being tested in interferon-free regimens in genotype 1 infections, with results expected next year. The FDA is due to rule on whether to approve the drug by December 8.

Analysts predict that sofosbuvir will reach multibillion annual sales at peak, with estimates ranging from $2 billion to $5 billion and even in excess of $10 billion a year in some cases. Gilead is competing with rival firms including AbbVie, Bristol-Myers Squibb and Boehringer Ingelheim to bring all-oral regimens with efficacy across the board in HCV, including genotype 1.

At the moment the standard of HCV care - namely a protease inhibitor (Merck & Co's Victrelis or Vertex' Incivek) plus pegylated interferon or ribavirin for 48 weeks - is "very, very difficult for a patient to undertake," said Gilead president John Milligan last month.

Combination therapy with oral antivirals could mean treatment for as little as 12 weeks, he noted. "That's 84 pills you have to take for a cure, [and] it’s a pretty good deal if we can get to that in the not too distant future," he said.

Meanwhile, following approximately one year behind sofosbuvir as a single agent is a fixed-dose combination of sofosbuvir plus NS5A inhibitor ledipasvir (GS-5885), which has been granted breakthrough status by the FDA and is in phase III testing. It is scheduled for filing in the second quarter of 2014.

Approval will reinforce Gilead's leading position in antivirals and consolidate its strong position in treatments for HIV, a category which is only around a quarter of the size of the HCV market.

HIV drugs account for the bulk of Gilead's sales at the moment at $4.4 billion out of total company turnover of a little over $5 billion in the first half of the year. Its dominant position in HIV has come from providing ever simpler treatment regimens based on fixed-dose combinations of antiviral agents.