Gilead Sciences Inc.’ AIDS drug Viread received the Food and Drug Administration’ s approval on Monday as hepatitis B treatment.

Viread is an antiretroviral drug, which has been available in Europe as a part of combination therapy for HIV infection in adults since 2001. The drug quickly became a top-selling anti-HIV treatment with sales of $783 million in 2004. Last year, the drug had about $613 million in sales, while Gilead’s total revenues were of $3.73 billion.

Hepatitis B is a serious liver disease, which affects about 400 million people globally and some 2 million in the United States. According to the Centers for Disease Control and Prevention, the disease can result in liver damage, liver failure, or liver cancer. The disease can be spread through blood, semen, or other body fluids.

Viread works by blocking an enzyme called HBV DNA polymerase, which is needed by the hepatitis B virus to replicate in liver cells, its maker said in a news release.

The approval was based on the results of two studies, which found that, “a significantly greater percentage of patients with chronic hepatitis B who received Viread achieved a complete response to treatment compared to those who received Hepsera.”

Hepsera is another Gilead’s drug for liver infections in adults.

Treatment with Viread can have as side effects abdominal pain, diarrhea, headache, dizziness, fatigue, inflammation of the nose or throat, back pain and skin rash.

Patients should have a HIV test before starting treatment with Viread, Gilead says.