ent-Entecavir is an enantiomeric impurity of the antiviral drug Entecavir. Entecavir is an oral antiviral drug used in the treatment of hepatitis B virus (HBV) infection. Entecavir is a reverse transcriptase inhibitor. It prevents the hepatitis B virus from multiplying and reduces the amount of virus in the body. More specifically, it is a deoxyguanosine analogue belonging to a class of carbocyclic nucleosides, that inhibits reverse transcription, DNA replication and transcription in the viral replication process.