By Ben Hirschler

LONDON Thu Aug 14, 2014 7:36pm EDT

(Reuters) – Gilead Sciences’ expensive new hepatitis C pill has been endorsed for use in certain patients by Britain’s healthcare cost-effectiveness watchdog, after the U.S. firm provided more information.

The National Institute for Health and Care Excellence (NICE) had told Gilead in June to come back with more data to support the use of Sovaldi, a drug whose sky-high U.S. price of $1,000 per pill has sparked fierce debate over costly modern medicines.

Carole Longson, director of the NICE Centre for Health Technology Evaluation, said on Friday it was now provisionally recommending Sovaldi, also known as sofosbuvir, as a cost-effective treatment for some people with chronic hepatitis C.

Gilead welcomed the decision to endorse Sovaldi as part of a combination treatment regimen, which it said would potentially make the drug available for the majority of hepatitis C patients.

The new drug is recommended for people chronically infected with certain strains, or genotypes, of the disease, which can cause liver cirrhosis and, in a small percentage of people, liver cancer. The conditions attached to its use vary according to a patient’s disease state and any past treatments.

Gilead argues its drug’s high price is justified by the near guarantee of a cure, far fewer side effects and the treatment’s ability to help patients avoid far more expensive hospital treatment, including potential liver transplants.

But the sheer cost of the drug – which has already sold $5.8 billion in its first six months, making it the most successful new drug launch ever – has fueled controversy. Two members of the U.S. Senate Finance Committee wrote to Gilead last month asking the company to justify the price.

In Britain, where NICE’s control over which drugs are used on the state health service exerts downward pressure on prices, Sovaldi is priced at 35,000 pounds ($58,400) for a 12-week course of treatment – 30 percent less than in the United States.

NICE was set up by the government in 1999 to decide in a rational way which drugs and treatments should be available on the National Health Service in England and Wales, making it an early pioneer of so-called healthcare technology assessment.

Since then it has had numerous run-ins with the pharmaceuticals industry, especially over cancer drugs.

The latest cancer drug row involves a decision, also announced on Friday, not to recommend the use of Johnson & Johnson’s prostate cancer medicine Zytiga before chemotherapy, even though it is already recommended for use afterwards.

J&J said it was very disappointed by the ruling, which comes hard on the heels of a rebuff for Roche’s new breast cancer drug Kadcyla last week.

(Editing by Raissa Kasolowsky)