indication

For the treatment of chronic hepatitis B in adult and adolescent patients ≥16 years of age with evidence of viral replication and either evidence of persistent elevations in serum aminotransferases (ALT or AST) or histologically active disease.

pharmacology

Telbivudine is a synthetic thymidine nucleoside analogue with activity against hepatitis B virus (HBV). Telbivudine is the unmodified β–L enantiomer of the naturally occurring nucleoside, thymidine. It undergoes phosphorylation via interaction with cellular kinases to form the active metabolite, telbivudine 5'-triphosphate.

mechanism of action

Telbivudine 5'–triphosphate inhibits HBV DNA polymerase (reverse transcriptase) by competing with the natural substrate, thymidine 5'–triphosphate. This leads to the chain termination of DNA synthesis, thereby inhibiting viral replication. Incorporation of telbivudine 5'–triphosphate into viral DNA also causes DNA chain termination, resulting in inhibition of HBV replication. Telbivudine inhibits anticompliment or second-strand DNA.

toxicity

There is no information on intentional overdose of telbivudine, but one subject experienced an unintentional and asymptomatic overdose. Healthy subjects who received telbivudine doses up to 1800 mg/day for 4 days had no increase in or unexpected adverse events. A maximum tolerated dose for telbivudine has not been determined.

biotransformation

No metabolites of telbivudine were detected following administration of [14C]–telbivudine in humans. Telbivudine is not a substrate, or inhibitor of the cytochrome P450 (CYP450) enzyme system.

absorption

Absorbed following oral administration. Telbivudine absorption and exposure were unaffected when a single 600–mg dose was administered with a high–fat (~55 g), high–calorie (~950 kcal) meal.

half life

Approximately 15 hours.

route of elimination

Telbivudine is eliminated primarily by urinary excretion of unchanged drug.