An acyclic nucleotide adenine analogue with potent antiviral activity. Adefovir is activated in vivo to a diphosphate metabolite which is incorporated into viral DNA, leading to viral RNA-dependent DNA polymerase inhibition, DNA chain termination and impairment of viral replication. This agent inhibits the reverse transcriptases of hepatitis B, herpes and HIV viruses, induces natural killer cell activity, and stimulates endogenous interferon production. Viral resistance to adefovir develops at a slower rate compared to other antivirals.