A synthetic thymidine nucleoside analogue with antiviral activity highly specific for the treatment of hepatitis B virus (HBV). Intracellularly, telbivudine is phosphorylated to its active metabolite, telbivudine triphosphate. The dideoxy telbivudine triphosphate competes with thymidine for incorporation into viral DNA, thereby causing DNA chain termination and inhibiting the function of HBV DNA polymerase (reverse transcriptase). This results in the blockade of HBV DNA replication and viral propagation.