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Pharmacology · Antituberculosis drugs

Ethambutol !

A first-line TB drug that protects the other drugs from resistance. Its hallmark risk is optic neuritis, with loss of red-green colour vision.

Updated 2026-11-01

  • Class: Antituberculosis drugs
  • Enzyme: Arabinosyltransferase EmbB (M. tuberculosis)
  • ATC code: J04AK02
  • WHO Model List of Essential Medicines

Also called: E, EMB

The figure shows ethambutol bound to the EmbA–EmbB arabinosyltransferase complex of M. tuberculosis (cryo-EM).

Target in 3D: Arabinosyltransferase EmbB (M. tuberculosis). PDB structure 7BVF (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Ethambutol blocks the arabinosyltransferases (encoded by the emb genes) that add arabinose to arabinogalactan, a polysaccharide that anchors mycolic acids to the cell wall. It is bacteriostatic at usual doses; its main role in the regimen is to stop resistance emerging to the companion drugs.

  1. Ethambutol blocks the EmbB arabinosyltransferase
  2. Arabinogalactan cannot be assembled
  3. The cell wall weakens and growth stops

Pharmacokinetics

Absorption
Good by mouth; aluminium hydroxide antacids lower it
Elimination
Kidney, largely unchanged; it accumulates in renal failure

Indications

Adverse effects

Common

  • Gastrointestinal upset, loss of appetite
  • Raised uric acid, sometimes gout
  • Peripheral neuropathy (numbness, tingling)
  • Headache, dizziness, confusion

Contraindications

  • Known optic neuritis, unless the team judges it necessary
  • People who cannot report vision changes (young children, unconscious patients)
  • Hypersensitivity to ethambutol

Key interactions

Aluminium hydroxide antacids
They lower ethambutol absorption: the doses are separated by several hours

What is monitored

  • Visual acuity and colour vision at baseline and during treatment
  • Kidney function (dose depends on it)
  • Liver tests and blood count periodically
  • Uric acid

Administration and safety

  • By mouth, usually within fixed-dose combinations
  • Kept apart from aluminium antacids
  • Dose depends on weight and kidney function; it is adjusted in renal failure

Nursing care

  • Teach to report blurred vision or trouble telling red from green at once
  • Do a simple acuity and colour check at visits when possible
  • Check creatinine before and during treatment
  • Ask about tingling in the feet and joint pain

Pregnancy and breastfeeding

Eye abnormalities have been reported in infants whose mothers received regimens that included ethambutol; the benefit of treating maternal tuberculosis is weighed against this.

Test yourself

Think of the answer, then tap the question to see it.

Which eye problem is typical of ethambutol and how does it show?

Optic neuritis: lower visual acuity and loss of red-green colour discrimination.

What is ethambutol's main role in the first-line regimen?

To protect the companion drugs from the emergence of resistance.

Why does kidney function matter with ethambutol?

It is cleared mostly by the kidney and accumulates in renal failure, which raises toxicity.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - ETHAMBUTOL HYDROCHLORIDE tablet (DailyMed (U.S. National Library of Medicine), 2024); WHO consolidated guidelines on tuberculosis: module 4: treatment and care (World Health Organization (WHO), 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 65 (McGraw Hill, 2023).

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Representative model, for educational purposes only.