1. Clinical Overview
Lamivudine is a synthetic nucleoside analogue reverse transcriptase inhibitor (NRTI) with potent activity against human immunodeficiency virus (HIV) and hepatitis B virus (HBV). It is phosphorylated intracellularly to its active 5'-triphosphate metabolite, lamivudine triphosphate, which inhibits viral DNA synthesis by terminating the nascent DNA chain. In India, it is a cornerstone of first-line antiretroviral therapy (ART) for HIV and a key component of HBV treatment, available as a low-cost generic medication.
| Onset | Duration | Bioavailability |
|---|---|---|
| Plasma concentration peaks within 0.5 to 1.5 hours post oral dose. Virological response in HIV/HBV is typically observed within 2-4 weeks. | Approximately 24 hours, supporting once-daily dosing for HBV and twice-daily dosing in standard HIV regimens. | 86% in adults, with minimal food interference. |
2. Mechanism of Action
Lamivudine is a prodrug. After cellular uptake, it is phosphorylated by host cell kinases to lamivudine triphosphate (L-TP). L-TP competitively inhibits the reverse transcriptase (RT) enzymes of HIV-1, HIV-2, and HBV by incorporating into the growing viral DNA chain. This incorporation causes chain termination because lamivudine lacks the 3'-OH group required for phosphodiester bond formation.
3. Indications & Uses
- Treatment of Human Immunodeficiency Virus (HIV-1 and HIV-2) infection in combination with other antiretroviral agents.
- Treatment of chronic Hepatitis B Virus (HBV) infection with evidence of active viral replication, elevated serum ALT, and histological evidence of active liver disease.
4. Dosage & Administration
Adult Dosage: HIV: 150 mg twice daily OR 300 mg once daily (as part of combination therapy). HBV: 100 mg once daily (Note: Indian brands commonly have 150mg; 100mg is the standard HBV dose, but 150mg is used in HIV/HBV co-infection as part of ART).
Administration: Can be taken with or without food. For consistent absorption, take at the same time(s) each day. The tablet should be swallowed whole with water.
5. Side Effects
Common side effects may include:
- Headache
- Nausea
- Diarrhea
- Fatigue
- Cough
- Nasal signs and symptoms
- Malaise
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Trimethoprim/Sulfamethoxazole (Cotrimoxazole) | Increases lamivudine AUC by ~40% due to competition for renal secretion. Clinical significance is minimal, but monitor for increased lamivudine side effects. | Moderate |
| Zidovudine (AZT) | Pharmacokinetic interaction is minimal. Used together as a foundational NRTI backbone in ART. Monitor for additive hematological toxicity (neutropenia, anemia). | Moderate |
| Ribavirin | Antagonistic antiviral effect in vitro; may reduce lamivudine efficacy. Use with caution in HIV/HCV co-infected patients. | Moderate |
| Other drugs excreted by active renal secretion (e.g., cimetidine) | Potential increase in lamivudine levels. Monitor. | Mild |
7. Patient Counselling
- DO take the medication exactly as prescribed, at the same times each day.
- DO continue taking lamivudine even if you feel well.
- DO inform all your healthcare providers you are taking lamivudine.
- DON'T stop taking lamivudine for Hepatitis B without consulting your doctor, as it can cause a dangerous flare-up of the disease.
- DON'T share your medication with anyone else.
- DON'T run out of medication; ensure timely refills.
8. Toxicology & Storage
Overdose: Limited data. Symptoms may include nausea, vomiting, dizziness, headache, and elevated liver enzymes. Neurological symptoms like peripheral neuropathy are possible at very high doses.
Storage: Store below 30°C in a cool, dry place, protected from light and moisture. Keep in the original container. Keep out of reach of children.