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Rifamycin Antibiotic Pregnancy: Caution — used in pregnancy for TB (benefit outweighs risk); neonatal vitamin K at birth (inhibits vitamin K-dependent clotting factors)

Rifampicin

Brand names: Rimactane, Rifadin

Adult dose

Dose: TB (standard): 600 mg OD or 10 mg/kg OD (max 600 mg/day) as part of RHZE regimen. Meningococcal prophylaxis: 600 mg BD × 2 days. Staphylococcal biofilm: 300–600 mg BD in combination.
Route: Oral (or IV for serious infections)
Frequency: OD (TB) or BD (prophylaxis/biofilm)
Max: 600 mg/day (standard); higher in some specialist protocols
Powerful CYP inducer — massive drug interactions. Always used in combination (monotherapy causes rapid resistance). Turns body fluids orange-red — warn patients. NEVER use as monotherapy.

Paediatric dose

Dose: 10 mg/kg
Route: Oral
Frequency: OD
Max: 600 mg/day
Concentration: 20 mg/ml
BNF for Children: TB treatment 10–20 mg/kg OD (max 600 mg) — calculator uses 10 mg/kg (conservative standard). Meningococcal prophylaxis: 10 mg/kg BD × 2 days (neonates: 5 mg/kg BD). Source: BNF for Children 2024; NICE NG33 TB; British Thoracic Society TB Guidelines

Dose adjustments

Renal

No dose adjustment required

Hepatic

Reduce dose in severe hepatic impairment — hepatically metabolised; also hepatotoxic

Paediatric weight-based calculator

BNF for Children: TB treatment 10–20 mg/kg OD (max 600 mg) — calculator uses 10 mg/kg (conservative standard). Meningococcal prophylaxis: 10 mg/kg BD × 2 days (neonates: 5 mg/kg BD). Source: BNF for Children 2024; NICE NG33 TB; British Thoracic Society TB Guidelines

Clinical pearls

  • Most potent CYP3A4, CYP2C9, P-gp inducer in clinical use — affects almost every co-prescribed drug
  • OCP: warn patients rifampicin makes the pill ineffective — use barrier contraception AND for 4 weeks after stopping
  • Warfarin: dose may need to be DOUBLED when starting rifampicin; carefully retitrate when stopping
  • Never use as monotherapy — rapid selection of resistant mutants within days

Contraindications

  • Active hepatic disease
  • Porphyria
  • Concurrent saquinavir/ritonavir (HIV protease inhibitors)

Side effects

  • Orange-red discolouration of urine, saliva, tears, sputum (harmless — warn patient; stains contact lenses)
  • Hepatotoxicity (check LFTs)
  • Influenza-like syndrome (intermittent regimens)
  • Thrombocytopenia
  • Interstitial nephritis (rare)
  • Immunological reactions (especially intermittent high-dose use)

Interactions

  • CYP inducers — multiple critical interactions: reduces levels of warfarin (double dose may be needed), OCP (use barrier contraception), ciclosporin/tacrolimus, antiretrovirals (most), statins, DOACs, phenytoin, corticosteroids, methadone, clarithromycin
  • Massive drug interaction list — always check BNF appendix before co-prescribing

Monitoring

  • LFTs (baseline, 2 weeks, then monthly during TB treatment)
  • Drug levels for co-medications (warfarin INR, ciclosporin levels, etc.)
  • Orange discolouration (reassure patient)
  • FBC (thrombocytopenia)

Reference: BNFc; BNF; NICE NG33 TB; British Thoracic Society TB Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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