RIFAMPIN

Clinical safety rating: safe

Human studies have proved safety

How it works

Inhibits DNA-dependent RNA polymerase in bacteria, blocking RNA synthesis.

What the body does with it

Metabolism	Primarily hepatic via deacetylation; induces CYP3A4, CYP2C9, and CYP2C19; undergoes enterohepatic circulation.
Excretion	Biliary excretion of unchanged drug (60–65%) and metabolites (15–20%); renal excretion of unchanged drug (15–20%) and metabolites (5–10%); fecal elimination of unabsorbed drug (≤5%).
Half-life	Terminal elimination half-life is 3–5 hours initially, decreasing to 2–3 hours after repeated dosing due to autoinduction of hepatic microsomal enzymes. In hepatic impairment, half-life may increase to 5–8 hours.
Protein binding	80–90% bound to albumin.
Volume of Distribution	Vd is 1.0–1.5 L/kg, indicating extensive tissue distribution (e.g., lungs, liver, macrophages, pleural fluid).
Bioavailability	Oral bioavailability is 90–95% (fasting state); reduced by 15–25% with high-fat meal.
Onset of Action	Oral: onset of antimycobacterial effect occurs within 1–2 hours after a single dose; IV: onset within 30–60 minutes.
Duration of Action	Duration of antimycobacterial activity is approximately 12–24 hours after a single dose, supporting once-daily dosing. Longer duration may occur in hepatic impairment.

Classification & Brands

Dosing & administration

Oral or IV: 600 mg once daily (10 mg/kg/day). For tuberculosis: 10 mg/kg (max 600 mg) once daily.

Dosage form	INJECTABLE
Renal impairment	No dose adjustment required for GFR >10 mL/min. For GFR ≤10 mL/min: reduce dose by 50% (300 mg daily). Not significantly removed by hemodialysis.
Liver impairment	Child-Pugh A: No adjustment. Child-Pugh B: Consider 50% dose reduction or extended interval. Child-Pugh C: Avoid use or use with extreme caution (monitor LFTs).
Pediatric use	10-20 mg/kg (max 600 mg) once daily orally or IV. For tuberculosis: 10-20 mg/kg (max 600 mg) daily.
Geriatric use	No specific dose adjustment; use normal adult dosing with monitoring for hepatotoxicity and drug interactions. Caution in renal impairment (GFR ≤10 mL/min requires dose reduction).

Use during pregnancy

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

Clinical note

A strong inducer of CYP450 enzymes decreasing levels of many drugs Can cause hepatotoxicity and orange discoloration of bodily fluids.

Breastfeeding	Rifampin is excreted into breast milk in small amounts (M/P ratio approximately 0.2-0.3). The American Academy of Pediatrics considers it compatible with breastfeeding. However, monitor infant for jaundice, drowsiness, or gastrointestinal disturbances. It is recommended to continue breastfeeding while on therapy.
Teratogenic Risk	Rifampin is generally considered safe in pregnancy. FDA Category C. First trimester: limited data suggest no increased risk of major malformations, but avoid if possible. Second and third trimesters: increased risk of postpartum hemorrhage due to vitamin K deficiency in the neonate; prophylactic vitamin K administered to the mother. Potential for neonatal bleeding.

Warnings & precautions

■ FDA Black Box Warning

Hepatotoxicity: severe and sometimes fatal hepatitis has been reported; monitor liver function closely.

Side Effect Profile

Common Effects	Hepatotoxicity
Serious Effects

Absolute Contraindications

["Hypersensitivity to rifampin or any rifamycins","Concomitant use with atazanavir, darunavir, fosamprenavir, saquinavir, tipranavir, and other protease inhibitors boosted with ritonavir","Severe liver disease with jaundice"]

Clinical Precautions

Precautions

["Hepatotoxicity, including fatal hepatitis","Hematologic reactions (thrombocytopenia, hemolytic anemia)","CNS effects (confusion, ataxia)","Renal impairment","Discoloration of bodily fluids (orange-red)","Potential for drug interactions due to enzyme induction"]

Clinical Tips & Counseling

Drug interactions

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