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Antituberculous Agents Pregnancy: Use with caution — benefits usually outweigh risks for active TB; associated with haemorrhagic disease of the newborn — give vitamin K to neonate at delivery; avoid in last 4 weeks of pregnancy if possible

Rifampicin

Brand names: Rifadin, Rimactane

Adult dose

Dose: 600 mg once daily (body weight above 50 kg); 450 mg once daily (body weight 50 kg or below)
Route: Oral (also IV available)
Frequency: Once daily on empty stomach
Max: 600 mg/day
Take 30 minutes before meals (food reduces absorption by 30%). Warn patient urine, tears, sweat, and saliva turn orange-red — stains contact lenses permanently. Co-prescribe pyridoxine with isoniazid combination.

Paediatric dose

Dose: 10 mg/kg once daily (max 600 mg) mg/kg
Route: Oral
Frequency: Once daily
Max: 600 mg/day
Liquid formulation available; shake well before use; seek specialist paediatric infectious disease opinion

Dose adjustments

Renal

No dose adjustment required — primarily hepatically metabolised and excreted in bile; use with caution in severe renal impairment

Hepatic

Use with caution — rifampicin is hepatotoxic; avoid in severe hepatic impairment or acute liver disease; baseline LFTs mandatory

Paediatric weight-based calculator

Liquid formulation available; shake well before use; seek specialist paediatric infectious disease opinion

Clinical pearls

  • DRUG INTERACTION KING: rifampicin is the most potent inducer of CYP enzymes known in clinical practice — affects CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP3A4, and P-glycoprotein; review EVERY concurrent medication before starting
  • CONTRACEPTIVE FAILURE: oral contraceptive failure during rifampicin is one of the most important MHRA warnings for TB treatment — women on hormonal contraception MUST be counselled to use additional non-hormonal contraception during treatment AND for 4 weeks after stopping rifampicin
  • ORANGE DISCOLOURATION: all body fluids turn orange-red — this is harmless and expected; warn patients before starting; permanently stains soft contact lenses (use glasses during treatment)
  • LTBI TREATMENT: 3-month course of rifampicin + isoniazid (3HR) is equally effective to 6-month isoniazid alone (6H) for LTBI; NICE NG33 recommends both as options; 3HR has better completion rates
  • Rifabutin: alternative to rifampicin with fewer CYP3A4 induction effects — preferred when used with HIV protease inhibitors or other sensitive CYP3A4 drugs; less orange discolouration
  • MHRA: rifampicin is listed as a critical medicine for TB; supply shortages may occur — notify Public Health England if supply issues arise

Contraindications

  • Known hypersensitivity to rifamycins
  • Jaundice or active hepatic disease
  • Acute porphyria
  • Concurrent use with strong CYP3A4-dependent drugs listed as contraindicated (see interactions)

Side effects

  • Hepatotoxicity (dose-related; combination with isoniazid increases risk)
  • Orange-red discolouration of urine, saliva, tears, sweat (inevitable — harmless)
  • Thrombocytopenia (especially with intermittent dosing regimens)
  • Flu-like syndrome (with intermittent use)
  • Hypersensitivity reactions (fever, rash)
  • Cholestatic jaundice

Interactions

  • POTENT CYP3A4/CYP2C9/P-gp INDUCER — most important drug interaction in all of medicine: reduces plasma levels of: warfarin (INR may halve), oral contraceptives (ABSOLUTE contraindication — use non-hormonal contraception), HIV antiretrovirals (critical), immunosuppressants (tacrolimus, ciclosporin halved), methadone, antifungals, statins, calcium channel blockers, antiepileptics, NOACs
  • Contraceptive pill — MUST inform patients: rifampicin renders oral/patch/ring contraception INEFFECTIVE — use condom or other barrier method for duration AND 4 weeks after stopping
  • Antiretrovirals — consult HIV specialist before starting TB treatment in HIV-positive patients; rifabutin may be substituted to reduce CYP interactions

Monitoring

  • LFTs (baseline, at 2 weeks for high-risk, then monthly — hepatotoxicity)
  • Full blood count (thrombocytopenia — especially intermittent regimens)
  • INR if on warfarin (major interaction — may need 2–3× warfarin dose increase)
  • Drug levels of critical concurrent medications (tacrolimus, ciclosporin, antiretrovirals)
  • Monthly sputum smear and culture (treatment response)

Reference: BNFc; BNF 90; NICE NG33 (TB 2016); WHO TB Guidelines 2022; MHRA SPC Rifadin; BTS TB Guidelines. Verify against your local formulary and the latest BNF before prescribing.

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Curated clinical cross-links plus same-class fallbacks.

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