LAMIVUDINE

Clinical safety rating: safe

Human studies have proved safety

How it works

Lamivudine is a nucleoside reverse transcriptase inhibitor (NRTI) that inhibits HIV reverse transcriptase and hepatitis B virus polymerase via incorporation into viral DNA, causing chain termination.

What the body does with it

Metabolism	Lamivudine is not significantly metabolized; it is primarily eliminated unchanged in urine via active renal secretion. Intracellularly, it is phosphorylated to its active triphosphate form.
Excretion	Renal: approximately 70% of the dose excreted unchanged in urine via glomerular filtration and active tubular secretion; biliary/fecal: minimal, less than 5%
Half-life	Terminal elimination half-life: 5-7 hours in adults; prolonged to 20-35 hours in patients with creatinine clearance <30 mL/min, necessitating dose adjustment
Protein binding	<36% bound to plasma proteins (primarily albumin) — low binding minimizes interactions
Volume of Distribution	1.3 L/kg; distributes widely into total body water, including cerebrospinal fluid (CSF-to-plasma ratio ~0.6)
Bioavailability	Oral: 86% (range 80-92%); no significant food effect
Onset of Action	Oral: antiviral effect begins within 1-2 hours due to intracellular phosphorylation; maximal effect by 4-6 hours
Duration of Action	Duration: approximately 12 hours based on intracellular triphosphate half-life of 10-15 hours; dosing interval is 12-24 hours depending on indication

Classification & Brands

Dosing & administration

150 mg orally twice daily or 300 mg orally once daily; for HIV-1 infection, 300 mg once daily or 150 mg twice daily; for hepatitis B, 100 mg orally once daily.

Dosage form	TABLET
Renal impairment	CrCl >=50 mL/min: no adjustment; CrCl 30-49 mL/min: 150 mg once daily (HIV) or 100 mg once daily (HBV); CrCl 15-29 mL/min: 150 mg first dose then 100 mg once daily (HIV) or 100 mg first dose then 50 mg once daily (HBV); CrCl 5-14 mL/min: 150 mg first dose then 50 mg once daily (HIV) or 100 mg first dose then 25 mg once daily (HBV); CrCl <5 mL/min: 150 mg first dose then 25 mg once daily (HIV) or 100 mg first dose then 10 mg once daily (HBV). Dosing recommendations per FDA labeling.
Liver impairment	No dosage adjustment required in patients with mild to moderate hepatic impairment (Child-Pugh A or B). Safety and efficacy in severe hepatic impairment (Child-Pugh C) not established; use with caution.
Pediatric use	For HIV-1: age 3 months to 16 years, dose 4 mg/kg (max 150 mg) orally twice daily; for body weight >=14 kg, 4 mg/kg twice daily; for weight 30 kg or more, adult dose may be used. For hepatitis B: pediatric patients not indicated per FDA; off-label use in children with chronic HBV (age >2 years) at 3 mg/kg once daily (max 100 mg).
Geriatric use

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Trimethoprim/sulfamethoxazole increases lamivudine exposure Severe acute exacerbations of hepatitis B have been reported upon discontinuation.

Breastfeeding	Lamivudine is excreted into human breast milk. M/P ratio approximately 0.6-3.3. Infant exposure is subtherapeutic. Limited data suggest no adverse effects in breastfed infants. CDC recommends breastfeeding for HIV-infected women on ART with undetectable viral load.
Teratogenic Risk	Lamivudine is FDA Pregnancy Category C. Human data show no increased risk of major birth defects in first trimester exposure based on Antiretroviral Pregnancy Registry. No evidence of fetal toxicity in second/third trimester. Animal studies showed embryotoxicity at high doses.

Warnings & precautions

■ FDA Black Box Warning

Posttreatment exacerbations of hepatitis B have been reported in patients who have discontinued lamivudine. Hepatic function should be monitored closely for at least several months in patients who discontinue anti-hepatitis B therapy.

Side Effect Profile

Common Effects	Hepatitis B
Serious Effects

Absolute Contraindications

Hypersensitivity to lamivudine or any component of the formulation.

Clinical Precautions

Precautions

["Lactic acidosis and severe hepatomegaly with steatosis, including fatal cases","Pancreatitis, particularly in pediatric patients with advanced HIV disease","Immune reconstitution syndrome","Hepatitis B exacerbation upon discontinuation","Risk of HIV resistance when used alone or with other NRTIs in HBV patients with unrecognized or untreated HIV"]

Clinical Tips & Counseling

Drug interactions

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