lamivudine

Lamivudine, marketed as Epivir for HIV infection and Epivir-HBV for hepatitis B, is a nucleoside analogue reverse transcriptase inhibitor (NRTI). It is used in combination antiretroviral regimens to treat HIV-1 and, separately, chronic hepatitis B in adults and children.

Lamivudine is a cytidine analogue that, once phosphorylated in cells, becomes lamivudine triphosphate. It competes with natural nucleotides and is incorporated into viral DNA by reverse transcriptase, causing chain termination and inhibition of viral replication.

In HIV infection, lamivudine is co-administered with other antiretrovirals and is commonly prescribed as 300 mg once daily or 150 mg twice daily, with dose adjustments for renal impairment. In chronic hepatitis B, it is used at 100 mg once daily; long-term monotherapy for HBV is discouraged due to the high risk of resistance.

Pharmacokinetics are favorable: oral bioavailability is high (about 80–90%), it is excreted largely unchanged by the kidneys, and it has minimal hepatic metabolism, with no major interactions via the cytochrome P450 system. Lamivudine is generally considered acceptable in pregnancy when the benefits outweigh potential risks.

Common adverse effects include headache, nausea, and fatigue. More serious but rare events include pancreatitis and lactic acidosis with hepatic steatosis, particularly when used with other NRTIs. Resistance can develop: in HIV, the M184V mutation reduces lamivudine susceptibility, and in HBV, resistance (rtM204V/I) emerges with long-term monotherapy, with partial cross-resistance to emtricitabine.