Antituberculous Agents 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

Brand names: Myambutol

Ethambutol is an oral antimycobacterial used as part of combination therapy for tuberculosis, typically during the intensive phase alongside other first-line agents.

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

Antituberculous therapy (respiratory TB). 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

Patient weight (kg)

Verify in a children's formulary

Contraindications

Hypersensitivity to the active substance 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, producing a bacteriostatic effect against Mycobacterium tuberculosis.

Prescribing in practice

Dose-related optic neuritis causing reduced visual acuity and red-green colour blindness is the key toxicity, so baseline visual assessment is required and the drug must be stopped if visual changes occur.
It is renally cleared and the dose must be reduced and monitored in renal impairment to avoid accumulation and ocular toxicity.
It must always be used within a multidrug regimen to prevent emergence of resistance, never as monotherapy.

Monitoring

Assess visual acuity and colour vision at baseline and review eyesight at each visit, with renal function monitoring particularly where impairment is present.

Counselling the patient

Report any blurring, change in colour vision or reduced sight immediately and stop the tablets.
Take all anti-tuberculosis medicines exactly as directed for the full course.
Children unable to report visual symptoms reliably need careful clinical consideration.

Evidence & guidelines

A standard component of WHO and NICE-endorsed first-line quadruple therapy for drug-sensitive tuberculosis.

Reference: NICE NG33; WHO TB Guidelines 2022; BTS TB Guidelines; MHRA SPC Myambutol; 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).

Curated clinical cross-links plus same-class fallbacks.

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