Entecavir hydrate is primarily used as an antiviral medication for the treatment of chronic hepatitis B virus (HBV) infection. It works by inhibiting the replication of the virus, thereby reducing the viral load in the body. This helps in slowing down the progression of liver damage, lowering the risk of complications such as cirrhosis and liver cancer. It is often prescribed for patients with evidence of active viral replication and liver inflammation. The medication is typically administered orally and is considered a first-line treatment due to its high efficacy and low resistance profile. Regular monitoring of liver function and viral load is essential during treatment to assess its effectiveness and make necessary adjustments.