Lamivudine Dosing and Administration: Practical Guide for Healthcare Providers

Quick Takeaways

• Lamivudine is a nucleoside reverse transcriptase inhibitor (NRTI) used for HIV and chronic hepatitis B.
• Standard adult dose: 300 mg orally once daily for HIV, 100 mg once daily for hepatitis B.
• Pediatric dosing is weight‑based (4 mg/kg for HIV, 2 mg/kg for hepatitis B) and must be rounded to the nearest 50 mg tablet or appropriate liquid volume.
• Renal impairment requires dose reduction: lamivudine dosing is cut in half when CrCl < 50 mL/min and stopped if CrCl < 10 mL/min.
• Take tablets with or without food; crush tablets only for oral solution if absolutely necessary.

Lamivudine is a synthetic nucleoside analogue that inhibits reverse transcriptase, a key enzyme for both HIV‑1 and hepatitis B virus replication. Marketed under the brand name Epivir, it has been part of first‑line antiretroviral therapy (ART) combos since its FDA approval in 1995. Because the drug is cleared primarily by the kidneys, dosing adjustments are crucial for patients with renal dysfunction, children, and pregnant women.

Why Lamivudine Matters in Modern Therapy

In the era of combination ART, lamivudine offers a low pill burden, excellent tolerability, and a modest resistance profile. For chronic hepatitis B, it provides rapid viral suppression and is often paired with tenofovir disoproxil fumarate (TDF) or tenofovir alafenamide (TAF) to achieve deep viral load reductions. Clinicians who understand the nuances of dosing can avoid sub‑therapeutic exposure-which fuels resistance-and prevent unnecessary toxicity.

Indications: HIV vs. Hepatitis B

Although the same molecule is used, the dose varies because the viral kinetic goals differ. For HIV, lamivudine is typically combined with other NRTIs such as tenofovir and a third agent (integrase inhibitor, NNRTI, or protease inhibitor). In hepatitis B monotherapy, the lower 100 mg dose still achieves >95 % viral suppression when paired with a second antiviral.

Standard Adult Dosing

Take the tablet at the same time each day. For hepatitis B patients who prefer tablets, split a 300 mg tablet into three equal parts-each part equals the 100 mg dose.

Pediatric Dosing Guidelines

Children < 15 kg receive weight‑based dosing. The CDC and WHO both recommend:

1. Calculate dose: 4 mg/kg for HIV, 2 mg/kg for hepatitis B, once daily.
2. Round the calculated dose to the nearest 50 mg tablet strength (or use the oral solution).
3. Re‑assess weight every 3‑6 months and adjust the dose accordingly.

Example: A 12‑kg child with HIV requires 48 mg. Rounding to the nearest 50 mg gives a 50 mg dose-administered as half of a 100 mg tablet or 2.5 mL of the 20 mg/mL solution.

Renal Impairment Adjustments

Since about 70 % of lamivudine is eliminated unchanged in urine, clinicians must modify the regimen for reduced creatinine clearance (CrCl):

• CrCl ≥ 50 mL/min - no change.
• CrCl 30‑49 mL/min - give 150 mg daily for HIV (or 50 mg for hepatitis B).
• CrCl 10‑29 mL/min - give 150 mg every 48 hours for HIV (or 50 mg every 48 hours for hepatitis B).
• CrCl < 10 mL/min - discontinue lamivudine; switch to a regimen that can be dosed safely in severe renal failure.

Use the Cockcroft‑Gault equation for adult patients and the Schwartz formula for children.

Special Populations

Pregnancy & Breastfeeding

Lamivudine crosses the placenta but is classified as Pregnancy Category C by the FDA (now replaced by the Pregnancy and Lactation Labeling Rule). Large cohort studies (e.g., the PROMISE trial) show no increase in congenital anomalies. The consensus among obstetricians and infectious disease experts is to continue the standard 300 mg dose throughout pregnancy and the postpartum period. Breast‑feeding mothers can also maintain the same dose; lamivudine appears in low concentrations in breast milk and is not associated with infant toxicity.

Hepatic Impairment

Because the liver contributes minimally to lamivudine clearance, no dose reduction is needed for mild to moderate hepatic dysfunction. In severe cirrhosis, monitor liver enzymes and viral load closely, but the standard dose remains appropriate.

Drug‑Drug Interactions

Lamivudine has a clean interaction profile. However, be aware of the following:

• Tenofovir - synergistic antiviral effect; no dose change needed.
• Zidovudine - both are NRTIs; combined use can increase the risk of mitochondrial toxicity, especially in patients with pre‑existing anemia.
• Didanosine - avoid co‑administration; increases pancreatitis risk.

Always review a patient’s full medication list, including over‑the‑counter supplements, before initiating lamivudine.

Monitoring & Follow‑Up

Effective monitoring ensures viral suppression and catches adverse events early:

1. Baseline labs: HIV RNA or HBV DNA, CD4 count (if HIV), liver function tests, serum creatinine, and pregnancy test (if applicable).
2. Week 4: Check renal function; adjust dose if CrCl drops.
3. Month 3 and thereafter: HIV RNA < 50 copies/mL or HBV DNA < 2000 IU/mL indicates successful therapy.
4. Every 6‑12 months: Evaluate for resistance, especially if viral load rebounds.

Adverse events are uncommon but may include headache, nausea, and mild fatigue. Discontinue if severe hypersensitivity (rash, facial swelling) occurs.

Practical Administration Tips

• Tablets can be taken with water; food does not affect absorption.
• Crush tablets only when a palatable oral solution is unavailable and the patient cannot swallow pills-inform the pharmacy to provide the liquid formulation if possible.
• Store tablets at room temperature, away from moisture; oral solution should be refrigerated after opening and used within 30 days.
• Educate patients to keep a medication diary; missed doses (>48 hours) may need a “restart” with a loading dose for HIV.

Frequently Asked Questions

Bottom Line

Getting lamivudine dosing right saves lives. Stick to weight‑based calculations for kids, adjust for renal function, keep an eye on pregnancy status, and pair it with a well‑chosen companion drug. When you follow these practical steps, you’ll see patients achieve undetectable viral loads and stay on therapy with minimal side effects.