1. Clinical Overview
A fixed-dose combination (FDC) of two nucleoside reverse transcriptase inhibitors (NRTIs) used as first-line antiretroviral therapy (ART) for the treatment of Human Immunodeficiency Virus (HIV) infection. Lamivudine and Zidovudine work synergistically to inhibit viral replication, thereby reducing viral load, increasing CD4 cell counts, and slowing disease progression. This combination is a cornerstone of public health programs in India under the National AIDS Control Organization (NACO) guidelines.
| Onset | Duration | Bioavailability |
|---|---|---|
| Plasma concentrations peak within 0.5 to 1.5 hours. Virological response (reduction in HIV RNA) is typically observed within 2-4 weeks of initiation. | Approximately 12 hours, supporting a twice-daily dosing regimen. | Lamivudine: ~86%; Zidovudine: ~64% (oral). Bioavailability of the combination is similar to individual components. |
2. Mechanism of Action
Both are nucleoside analogues that require intracellular phosphorylation to their active triphosphate forms. These active metabolites competitively inhibit the HIV reverse transcriptase enzyme and act as chain terminators during viral DNA synthesis, thereby halting viral replication.
3. Indications & Uses
- Treatment of Human Immunodeficiency Virus (HIV-1) infection in adults and children (in combination with other antiretroviral agents).
- Prevention of maternal-to-child transmission (PMTCT) of HIV during pregnancy and labor.
4. Dosage & Administration
Adult Dosage: One tablet (Lamivudine 150mg + Zidovudine 300mg) orally, twice daily.
Administration: Can be taken with or without food. Swallow whole with water. Maintain a strict 12-hourly schedule to ensure consistent drug levels. If a dose is missed, take it as soon as remembered, but if it is almost time for the next dose, skip the missed dose. Do not double the dose.
5. Side Effects
Common side effects may include:
- Headache
- Nausea
- Malaise/Fatigue
- Insomnia
- Nasal symptoms
- Cough
- Mild gastrointestinal disturbances
- Hyperpigmentation of nails/skin (common in Indian population)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Ganciclovir/Valganciclovir | Additive myelosuppression (severe neutropenia, anemia). | Major |
| Ribavirin | Antagonistic effect on Zidovudine's antiviral activity; may increase risk of lactic acidosis. | Major |
| Stavudine (d4T) | Pharmacological antagonism; concurrent use is contraindicated. | Major |
| Doxorubicin | May antagonize the anti-HIV effect of Zidovudine. | Moderate |
| Phenytoin | May alter phenytoin levels; Zidovudine levels may be increased. | Moderate |
| Probenecid | Inhibits glucuronidation of Zidovudine, increasing its toxicity risk. | Moderate |
| Trimethoprim-Sulfamethoxazole | Increases Lamivudine levels by ~40%. Usually safe but monitor for Lamivudine toxicity in renal impairment. | Moderate |
| Other Nephrotoxic drugs (e.g., Aminoglycosides, Amphotericin B) | May increase risk of renal impairment, affecting Lamivudine excretion. | Moderate |
7. Patient Counselling
- DO take your medicine at the same times every day, exactly as prescribed. Lifelong adherence is critical.
- DO NOT stop taking this medicine without consulting your doctor, especially if you have Hepatitis B.
- DO inform all your healthcare providers (doctors, dentists) that you are taking this HIV medication.
- DO use barrier protection (condoms) to prevent HIV transmission to others, as this medicine does not prevent sexual transmission.
- DO NOT share your medication with anyone else.
8. Toxicology & Storage
Overdose: Nausea, vomiting, lethargy, headache, dizziness, bone marrow suppression (severe anemia, neutropenia), hepatic dysfunction, lactic acidosis, and peripheral neuropathy.
Storage: Store below 30°C in a cool, dry place, protected from light and moisture. Keep in the original blister pack or container. Keep out of reach of children. Do not use after the expiry date printed on the pack.