(Adds competitive details, analyst comment, updates shares)
By Ransdell Pierson and Bill Berkrot
May 2 (Reuters) - Gilead Sciences Inc on Thursday said almost all patients taking a fixed-dose combination of two of its experimental hepatitis C drugs appeared to have eliminated the liver virus after either eight weeks or 12 weeks of treatment in a small mid-stage study.
The data should strengthen the widely held perception that Gilead is leading the race among many companies to bring to market a highly curative, all-oral regimen with shorter treatment durations for the serious liver disease. Gilead shares rose 5 percent after the data was released.
Calling them "excellent results," Stifel analyst Joel Sendek said in a research note, "We see Gilead further increasing the pressure on its hepatitis C competitors with positive Phase II Lonestar trial data evaluating a short 8-week regimen of sofosbuvir plus ledipasvir."
AbbVie and Bristol-Myers Squibb are also developing highly promising all-oral hepatitis C treatments, seen as not far behind Gilead. But those regimens require patients to take many more pills each day than does Gilead's.
The Gilead combination pill is taken once a day and is being tested with and without the older drug ribavirin, which is typically taken twice a day.
Current treatments introduced in 2011 must still be taken with ribavirin and the injected drug interferon, which causes miserable flu-like symptoms and leads many patients to delay or discontinue treatment. The current standard treatment takes either 24 or 48 weeks. The new combinations are attempting to cut the duration to 12 weeks, or as few as eight.
Gilead is expected to have a new hepatitis C treatment approved next year.
Based on the favorable interim data from the Lonestar trial of 60 previously untreated patients, Gilead said it plans to conduct a third late-stage study of the once-daily fixed-dose combination tablet pairing sofosbuvir and ledipasvir.
The new Phase III trial, called ION-3, will enroll 600 patients new to treatment who have the most common and difficult to treat genotype 1 form of hepatitis C, Gilead said.
It will evaluate the combination tablet for eight weeks of treatment, with and without ribavirin, as well as for 12 weeks without ribavirin. An all-oral combination with high cure rates that does not include ribavirin, which also has some tough to tolerate side effects, would be viewed by doctors and patients as a huge advantage over those that include the older drug.
Wall Street expects any approved oral regimen for hepatitis C to garner billions of dollars in annual sales.
Gilead said all 19 patients in the Lonestar trial who took its 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. They will be followed for a further 20 weeks. Any patient in whom the virus is undetectable 24 weeks after completing treatment is deemed to be cured.
In another arm of the trial, 40 of 41 patients who took the tablet for eight weeks were deemed free of the virus eight weeks after they completed treatment. The one patient who relapsed was from a group that took the combo tablet but not ribavirin, the company said. That may suggest that 12 weeks of treatment will be necessary if ribavirin is not part of the regimen.
Gilead also tested 40 patients who had failed to be helped by current treatments, half of them with cirrhosis - an indication of advanced disease. Ninety-five percent of those more difficult to treat patients had no sign of the virus four weeks after completing 12 weeks of the combination pill either with or without ribavirin, according to preliminary results.
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.
Gilead shares were up $2.49 at $52.62 in midday trading on Nasdaq. (Reporting By Ransdell Pierson and Bill Berkrot; Editing by Gerald E. McCormick and Nick Zieminski)