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Antimycobacterial (TB) Pregnancy: Not recommended during pregnancy and in women of childbearing potential unless the potential benefit to the mother outweighs possible risks (UK SPC). Breast-feeding not recommended unless benefit to the child outweighs risks.

Ethambutol hydrochloride

Brand names: Myambutol

Ethambutol hydrochloride is a first-line oral antimycobacterial used as part of combination therapy for active tuberculosis, typically during the initial intensive phase alongside rifampicin, isoniazid and pyrazinamide.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 15 mg/kg
Route: oral
Frequency: single daily dose
Dose adjusted to body weight. Adults, primary treatment and prophylaxis: single daily oral dose of 15 mg/kg, with concomitant antituberculous drugs at their recommended levels. Re-treatment: 25 mg/kg single daily dose for the first 60 days, then reduce to 15 mg/kg. Elderly: as for adults, but decreased renal function may require adjustment based on blood levels; give once daily. Renal impairment: preferably avoid; if used and creatinine clearance <30 mL/min, use 15–25 mg/kg (max. 2.5 g) three times a week with plasma ethambutol concentration monitoring.

Paediatric dose

Dose: 25 mg/kg
Route: oral
Frequency: single daily dose
Children, primary treatment and re-treatment: 25 mg/kg single daily oral dose for the first 60 days, then reduce to 15 mg/kg. For prophylaxis: single daily dose of 15 mg/kg. (US labelling states ethambutol is not recommended for pediatric patients under 13 years as safe conditions have not been established — verify against a children's formulary.)

Dose adjustments

Renal

Preferably avoid in renal impairment. If used and creatinine clearance <30 mL/min, use 15–25 mg/kg (max. 2.5 g) three times a week and monitor plasma ethambutol concentration.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Paediatric weight-based calculator

Children, primary treatment and re-treatment: 25 mg/kg single daily oral dose for the first 60 days, then reduce to 15 mg/kg. For prophylaxis: single daily dose of 15 mg/kg. (US labelling states ethambutol is not recommended for pediatric patients under 13 years as safe conditions have not been established — verify against a children's formulary.)

Verify in a children's formulary

Contraindications

  • Hypersensitivity to the drug or to any of the excipients
  • Known optic neuritis and poor vision, unless clinical judgement determines it may be used

Side effects

  • Optic neuritis (decreased visual acuity, loss of vision, scotoma, colour blindness, visual field defect, eye pain) — uncommon
  • Peripheral neuropathy, numbness, paraesthesia of the extremities — rare
  • Hyperuricaemia — uncommon
  • Thrombocytopenia — rare
  • Rash, pruritus, urticaria — rare; severe cutaneous reactions (SJS, TEN, DRESS) reported

Interactions

  • Aluminium hydroxide (antacids) may impair absorption of ethambutol

Clinical monograph

How it works

It inhibits arabinosyl transferases involved in mycobacterial cell wall arabinogalactan synthesis, impairing cell wall assembly and exerting a bacteriostatic effect on dividing mycobacteria.

Prescribing in practice

  • Dose-related optic neuropathy is the key hazard: assess visual acuity and colour vision before treatment and warn the patient to stop and seek review immediately if vision or colour perception changes.
  • Renally excreted, so the dose must be reduced and exposure monitored in renal impairment to limit ocular toxicity.
  • Always prescribe as part of a multi-drug regimen to prevent emergence of resistance, never as monotherapy.

Monitoring

Baseline and periodic visual acuity and red-green colour discrimination testing is required, with renal function monitored to guide dosing.

Counselling the patient

  • Report any blurring of vision or difficulty distinguishing red and green at once.
  • Take all your TB medicines together for the full course even when you feel well.
  • Children who cannot reliably report visual changes need careful specialist oversight.

Evidence & guidelines

Ethambutol is a WHO- and NICE-endorsed component of standard quadruple-therapy regimens for drug-susceptible tuberculosis.

Reference: NICE NG33; BTS/SIGN TB guidelines; UKHSA TB strategy; SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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