Hepatitis B is inflammation of the liver that is caused by a virus. The virus spreads through contact with infected body fluids. Most people who get hepatitis B recover within a few months, but some develop chronic infection. Chronic infection increases risk for liver failure and liver cancer. Persons with chronic infection often have virus-related protein substances in their blood (called hepatitis B surface antigens and e antigens) for many years. When an e antigen is present, it usually means that the person has very active liver disease and a lot of virus present. Doctors often treat these patients with powerful antiviral drugs. However, some patients develop viral forms (mutants) that are resistant to 1 or more antiviral drugs. To help suppress virus levels, prevent resistance, and improve outcomes, doctors might use different types of antiviral drugs or switch drugs during treatment. Few studies have assessed the benefits and harms of switching among different antiviral therapies for chronic hepatitis B.