A synthetic analog of 2-deoxyguanosine with antiviral activity against hepatitis B virus (HBV). Entecavir is activated in vivo to a 5-triphosphate metabolite. In turn, the triphosphate form competes with the natural substrate deoxyguanosine triphosphate (dGTP) for incorporation into viral DNA. The incorporation of the activated triphosphate metabolite of entecavir inhibits the reverse transcriptase (RT) viral RNA-dependent HBV DNA polymerase and, so, the replication of viral DNA and transcription.