The US Food and Drug Administration (FDA) approved Viread – an antiretroviral drug which has been available in Europe as a part of combination therapy for HIV infection in adults since 2002 – in 2001. The drug was initially approved by the FDA for about 40 percent of AIDS patients, but the company marketed it for all AIDS patients. The drug made by Gilead quickly became a top-selling anti-HIV treatment.

Gilead became one of the nation’s leading sellers of AIDS medications. In April, the European Commission approved Viread to treat chronic hepatitis B.

Gilead had another product, Hepsera, to treat the liver infections in adults. A study conducted by the company showed superior results in case of treatment with Viread than in case of treatment with Hepsera.

These results helped Viread to have the basis to apply to regulatory authorities in the United States and European Union, in order to market Viread as a treatment for HBV. The FDA’s approval was based on these trials that showed that Viread was more effective than Hepsera at combating liver inflammation and scarring caused by hepatitis B.

On Monday, the 9th US Circuit Court of Appeals in San Francisco reinstalled a lawsuit against Gilead that claimed the drug maker mislead investors about demand for Viread by allegedly marketing Viread for “off-label” uses.

Hepatitis B infection affects about 1.25 million Americans, with about 46,000 new cases a year, according to the US Centers for Disease Control and Prevention.

“Viread will be an important new treatment option and its approval represents a significant step forward in the fight against chronic hepatitis B,” the company said in a statement.