Entecavir is an antiviral medicine used to treat chronic hepatitis B virus (HBV) infection. It works by blocking the activity of the virus in the body and preventing further damage to the liver. Entasvir is available in tablet form and is taken once a day. This medicine can help reduce the amount of virus in the body and reduce the risk of serious liver problems. Entavir is a prescription drug, so talk to your doctor to see if it's right for you.