How the dose is calculated
This calculator covers rifampicin's contact-prophylaxis regimens (meningococcal and Hib, each with a reduced neonatal dose alongside the standard infant/child dose) and a simplified single-drug reference dose for its role in tuberculosis treatment. Real-world TB treatment is normally given as a fixed-dose combination (FDC) tablet dosed by weight-band tables rather than rifampicin alone — confirm the exact FDC dose against the current national/WHO weight-band table before prescribing.
Typical dosing by indication
| Indication | Dose | Frequency | Max |
|---|---|---|---|
| Meningococcal prophylaxis — infant & child | 20 mg/kg/day | every 12h (2×/day) for 2 days | 1200 mg/day |
| Meningococcal prophylaxis — neonate | 10 mg/kg/day | every 12h (2×/day) for 2 days | — |
| Hib prophylaxis — infant & child | 20 mg/kg once daily | once daily for 4 days | 600 mg/day |
| Hib prophylaxis — neonate | 10 mg/kg/day | every 12h (2×/day) for 4 days | — |
| Tuberculosis (single-drug reference) | 10 mg/kg/day, empty stomach | once daily, as part of multidrug regimen | 600 mg/day |
The neonatal dose for both prophylaxis indications is halved compared with the infant/child dose (10 vs 20 mg/kg/day), reflecting reduced drug-metabolising capacity in this age group, but keeps the same twice-daily frequency and course length as the corresponding infant/child regimen.
Clinical use
- Meningococcal contact prophylaxis is given to close contacts of a confirmed case as soon as possible, ideally within 24 hours of diagnosis, for the short 2-day course shown above.
- Haemophilus influenzae type b (Hib) contact prophylaxis follows a longer 4-day course, used for household contacts including an unvaccinated or incompletely vaccinated young child in the household.
- For tuberculosis, rifampicin (10 mg/kg/day, range 8–12 mg/kg, max 600 mg/day) is always given as part of a multidrug regimen, on an empty stomach (at least 30 minutes before food) to maximise absorption — never as monotherapy, which rapidly selects for resistance.
- Rifampicin is a potent inducer of hepatic CYP450 enzymes, significantly reducing the effectiveness of many drugs including oral contraceptives, warfarin, and some antiretrovirals — review the full medication list before prescribing.
- Harmlessly turns urine, tears, sweat, and contact lenses orange-red — warn patients in advance to avoid alarm.
Frequently asked questions
What is rifampicin used for in this calculator?
This calculator covers rifampicin's use as short-course prophylaxis for close contacts of confirmed meningococcal disease or Haemophilus influenzae type b (Hib) infection (with separate neonatal and infant/child doses), plus a simplified single-drug reference dose for tuberculosis — real TB treatment normally uses a fixed-dose combination tablet dosed from a weight-band table rather than rifampicin alone.
Why are the meningococcal and Hib prophylaxis courses different lengths?
They're separate, independently established regimens — meningococcal prophylaxis uses a twice-daily dose for 2 days, while Hib prophylaxis uses the same twice-daily neonatal dose (or once-daily infant/child dose) for 4 days. Both are effective for their specific indication when given as designed.
Why is the neonatal dose lower than the infant/child dose?
Neonates have reduced drug-metabolising capacity compared with older infants and children, so the same mg/kg/day dose used in older children would risk higher drug exposure — the neonatal dose is halved (10 vs 20 mg/kg/day) for both meningococcal and Hib prophylaxis, while keeping the same frequency and course length.
What is the rifampicin dose for tuberculosis?
10 mg/kg/day (range 8–12 mg/kg/day), up to a maximum of 600 mg/day, given once daily on an empty stomach, always as part of a multidrug regimen — never alone. In practice this is usually delivered as a fixed-dose combination (FDC) tablet dosed by weight band rather than as rifampicin alone; a common adult FDC dose is around 300–450 mg, close to a standalone 300mg rifampicin dose for lower-weight adults — confirm the exact FDC product and weight band against current national/WHO TB guidelines.
Why does rifampicin turn urine and tears orange?
This is a harmless, expected effect of the drug's own colour being excreted in body fluids — it doesn't indicate liver injury or any other problem, but patients should be warned in advance so it isn't mistaken for something concerning.
Does rifampicin interact with the contraceptive pill?
Yes — rifampicin strongly induces liver enzymes that break down oestrogen and progestogen, significantly reducing the effectiveness of hormonal contraception. Patients should be advised to use an additional or alternative contraceptive method during and shortly after treatment.
References
- Centers for Disease Control and Prevention. Meningococcal Disease — Chemoprophylaxis Guidance.
- American Academy of Pediatrics Red Book — Haemophilus influenzae Infections.
- British National Formulary for Children (BNFc) — Rifampicin.