Lamivudine (BCH-189) is a reverse transcriptase inhibitor and ZALCITABINE analog in which a sulfur atom replaces the 3' carbon of the pentose ring. It is used to treat HIV disease.

Lamivudine exhibits selective inhibitory activity against deoxycytidine kinase, an unusual substrate for the non-natural L-isomer of dNTPs preferred by HBV polymerase. The anti-HBV activity of PCV is attributed to the broad substrate specificity of deoxycytidine kinase and an unusual substrate preference of HBV polymerase for the non-natural L-conformation of dNTPs. The anti-HBV efficacy of PCV appears to rely on multiple factors, including optimal phosphorylation (sufficient for antiviral activity but not cytotoxicity), the extended intracellular half-life of PCV-TP, and the ability of PCV-TP to inhibit the initiation of HBV RT as well as its RT and DNA polymerase activities. Combined use of Lamivudine and Cidofovir synergistically inhibits replication of duck hepatitis B virus and is more effective in reducing the persistent covalently closed circular (CCC) DNA form of DHBV than when used separately. In PBMCs, Lamivudine inhibits HIV-1 p24 antigen production with ED50s ranging from 0.07 μM to 0.2 μM.