Clinical safety rating: caution
Essential component of TB treatment (HRZE regimen) safe to use in pregnancy. No established teratogenicity at standard doses. At term, rifampicin induces fetal CYP enzymes and can deplete vitamin K-dependent clotting factors — administer prophylactic vitamin K (10 mg IM) to the neonate at birth if the mother was on rifampicin near delivery. Also a potent enzyme inducer that reduces levels of many coadministered drugs (e.g., reduces hormonal contraceptive efficacy).
Inhibits bacterial DNA-dependent RNA polymerase by binding to the beta subunit, thereby blocking RNA transcription.
| Metabolism | Primarily hepatic via deacetylation; undergoes extensive enterohepatic recirculation. Induces CYP3A4, CYP2C9, CYP2C19, CYP1A2, and P-glycoprotein. |
| Excretion | Primarily hepatic (biliary) excretion into feces; about 60-65% as unchanged drug and metabolites. Renal elimination accounts for approximately 30% (mostly as metabolites). <5% excreted unchanged in urine. |
| Half-life | Terminal elimination half-life is 3-5 hours initially, but decreases to 2-3 hours after repeated dosing due to auto-induction of hepatic enzymes. Clinically significant for daily dosing and need for consistent timing. |
| Protein binding | 89% bound, primarily to albumin. |
| Volume of Distribution | 1.6 L/kg (range 1.3-2.0 L/kg), indicating extensive tissue distribution and penetration into cells, including macrophages. |
| Bioavailability | Oral: 90-95% (well-absorbed). Food reduces absorption slightly but not clinically significant. IV: 100%. |
| Onset of Action | Oral: 1-2 hours for antimycobacterial effect. IV: immediate. Intrathecal: not applicable. |
| Duration of Action | Approximately 12-24 hours; auto-induction reduces duration of effective concentrations. Serum levels remain above MIC for most of the dosing interval with daily dosing. |
| Molecular Weight | 822.94 |
600 mg orally or intravenously once daily
| Renal impairment | No dose adjustment required for renal impairment; caution in severe renal failure (GFR <30 mL/min) due to accumulation of metabolite; monitor closely |
| Liver impairment | Child-Pugh Class A: no adjustment; Child-Pugh Class B: reduce to 10 mg/kg (max 600 mg) daily or use every other day; Child-Pugh Class C: use with extreme caution, consider dose reduction to 10 mg/kg twice weekly or alternative agent |
| Pediatric use | 10-20 mg/kg (max 600 mg) orally or intravenously once daily; neonates: 10 mg/kg once daily |
| Geriatric use | Start at lower end of dosing range (300-450 mg daily) due to age-related decline in hepatic function and potential for drug interactions; monitor for hepatotoxicity and adjust based on tolerance |
| 1st trimester | Use only if clearly needed; potential for teratogenicity (limb reduction defects) in animal studies, but human data limited. Risk-benefit assessment required. |
| 2nd trimester | Generally acceptable if indicated; no known increased risk of fetal malformations from human data. Monitor for maternal hepatotoxicity. |
| 3rd trimester | Use with caution near term; may cause hemorrhage in neonate due to vitamin K antagonism. Administer vitamin K to mother if indicated. |
Clinical note
Essential component of TB treatment (HRZE regimen) safe to use in pregnancy. No established teratogenicity at standard doses. At term, rifampicin induces fetal CYP enzymes and can deplete vitamin K-dependent clotting factors — administer prophylactic vitamin K (10 mg IM) to the neonate at birth if the mother was on rifampicin near delivery. Also a potent enzyme inducer that reduces levels of many coadministered drugs (e.g., reduces hormonal contraceptive efficacy).
| Placental transfer | Crosses placenta readily; fetal serum concentrations reach approximately 33% of maternal levels. |
■ FDA Black Box Warning
Rifampicin should not be used in patients with pre-existing liver disease unless the expected benefits outweigh the risks. Severe hepatic injury, including fatalities, has been reported.
| Serious Effects |
Known hypersensitivity to rifamycinsActive liver disease (acute hepatitis)Severe hepatic impairment (Child-Pugh class C)PorphyriaConcomitant use with ritonavir-boosted protease inhibitors (e.g., saquinavir/ritonavir) due to hepatotoxicity risk
| Precautions | Hepatotoxicity, including fatal hepatitis; monitor liver function tests. Discontinue if signs of hepatocellular damage occur. Thrombocytopenia, hemolytic anemia, and renal failure may occur. Use with caution in patients with hepatic impairment. Rifampicin may produce a reddish-orange discoloration of urine, sweat, sputum, tears, and contact lenses. |
| Food/Dietary | Take on an empty stomach to enhance absorption. Avoid high-fat meals as they can reduce peak concentrations. Separate from antacids by at least 2 hours. |
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| Breastfeeding |
| Small amounts excreted into breast milk; generally considered compatible with breastfeeding. Monitor infant for jaundice, liver enzyme abnormalities, or gastrointestinal disturbances. Consider lowest effective dose. |
| Lactation Rating | L2 |
| Teratogenic Risk | Rifampicin crosses the placenta. First trimester: Increased risk of neural tube defects, cleft palate, and cardiovascular malformations based on animal studies; human data limited but possible. Second and third trimesters: Associated with increased risk of limb reduction defects and intracranial hemorrhage in neonates; may cause hemorrhagic disease due to vitamin K deficiency. Overall, use only if clearly needed. |
| Fetal Monitoring | Monitor liver function tests (ALT, AST, bilirubin) and renal function regularly. Check complete blood count (CBC) with differential for thrombocytopenia or leukopenia. Assess prothrombin time/INR due to risk of hemorrhagic disease. Monitor fetal growth and amniotic fluid volume via ultrasound. In neonates, monitor for signs of hemorrhage or kernicterus. |
| Fertility Effects | Rifampicin may induce hepatic enzymes and reduce the efficacy of hormonal contraceptives, potentially increasing the risk of unintended pregnancy. No direct evidence of impaired fertility in humans, but animal studies have shown alterations in estrous cycle and fertility at high doses. |
| Clinical Pearls | Rifampicin is a potent inducer of CYP450 enzymes (especially CYP3A4) and P-glycoprotein, significantly reducing the efficacy of oral contraceptives, warfarin, methadone, antiretrovirals, and many other drugs. It causes reddish-orange discoloration of urine, sweat, tears, and contact lenses. Monitor liver function tests due to risk of hepatotoxicity, especially when combined with isoniazid. Administer on an empty stomach for optimal absorption; avoid antacids within 2 hours. |
| Patient Advice | Take rifampicin on an empty stomach, at least 1 hour before or 2 hours after a meal. · Do not skip doses; complete the full course as prescribed. · Urine, sweat, tears, and feces may turn reddish-orange; this is harmless and expected. · Inform your doctor if you are using birth control pills; an alternative method may be needed. · Avoid alcohol and acetaminophen while on this medication to reduce liver strain. · Report any signs of liver problems: yellowing of skin/eyes, dark urine, abdominal pain, or persistent nausea. |