The US Food and Drug Administration approved Gilead’s HIV drug Viread for the treatment of chronic hepatitis B in adults. The FDA’s approval was based on trials and studies conducted by the company that showed superior results in case of hepatitis B treatment with Viread, than in case of treatment with Hepsera (adefovir dipivoxil), a prescription medicine that is also used to treat chronic infection with hepatitis B. Hepsera helps stop hepatitis B virus (HBV) from multiplying by blocking HBV DNA polymerase, an enzyme necessary for the replication of the virus in the body, according to Hepsera’s manufacturer.

According to the Gilead’s news release, studies showed “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.”

Viread works on the same principle: it blocks the enzyme called HBV DNA polymerase, which is needed by the hepatitis B virus to replicate in liver cells. As a treatment for HIV infection in adults (the medicine won FDA’s approval in 2001), Viread is always used in combinations with other antiretroviral drugs to treat people with HIV-1 infection. Gilead recommends HIV tests for all hepatitis B patients before starting treatment with Viread.

Chronic hepatitis B affects about 400 million people globally and some 2 million in the United States. The disease can cause long-term health problems, including liver damage, liver failure, liver cancer, and it can be fatal, according to the US Centers for Disease Control and Prevention.