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# 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](https://durgical.com/en/pharmacology/classes/antituberculosis-drugs/)
- Enzyme: Arabinosyltransferase EmbB (M. tuberculosis)
- ATC code: J04AK02
- WHO Model List of Essential Medicines

Also called: E, EMB

✂**Arabinosyltransferase EmbB (M. tuberculosis)**Ethambutol

ⓘ 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](https://www.rcsb.org/structure/7BVF) · Drag to rotate · pinch to zoom

## 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.

- Ethambutol blocks the EmbB arabinosyltransferase
- Arabinogalactan cannot be assembled
- 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

- Tuberculosis: intensive phase (HRZE) [Tuberculosis →](https://durgical.com/en/conditions/tuberculosis/)
- Pulmonary tuberculosis [Pulmonary tuberculosis →](https://durgical.com/en/conditions/pulmonary-tuberculosis/)
- Spinal tuberculosis (Pott disease) [Spinal tuberculosis (Pott disease) →](https://durgical.com/en/conditions/spinal-tuberculosis/)
- Mycobacterium avium complex and other nontuberculous mycobacterial infections, combined [Nontuberculous mycobacterial infections (MAC, M. abscessus, Buruli ulcer) →](https://durgical.com/en/conditions/nontuberculous-mycobacterial-infections/)

## Adverse effects

### Common

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

### Serious (rare, important)

- Optic neuritis: falling visual acuity and loss of red-green colour discrimination; usually reversible if stopped early, but blindness has been reported
- Liver toxicity
- Severe hypersensitivity and blood count drops

## 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.

## Memory aid

EYE-thambutol: keep an eye on the eyes, especially red and green.

## 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.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/ethambutol/)

## Related drugs

- [Isoniazid](https://durgical.com/en/pharmacology/isoniazid/)
- [Rifampicin](https://durgical.com/en/pharmacology/rifampicin/)
- [Pyrazinamide](https://durgical.com/en/pharmacology/pyrazinamide/)

## Related conditions

- [Tuberculosis](https://durgical.com/en/conditions/tuberculosis/)
- [Pulmonary tuberculosis](https://durgical.com/en/conditions/pulmonary-tuberculosis/)
- [Spinal tuberculosis (Pott disease)](https://durgical.com/en/conditions/spinal-tuberculosis/)
- [Nontuberculous mycobacterial infections (MAC, M. abscessus, Buruli ulcer)](https://durgical.com/en/conditions/nontuberculous-mycobacterial-infections/)

[← Back to the class: Antituberculosis drugs](https://durgical.com/en/pharmacology/classes/antituberculosis-drugs/)

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](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c732b415-e1f9-478f-896d-1dc8b6362da4) (DailyMed (U.S. National Library of Medicine), 2024); [WHO consolidated guidelines on tuberculosis: module 4: treatment and care](https://www.who.int/publications/i/item/9789240107243) (World Health Organization (WHO), 2025); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=J04AK02) (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.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/ethambutol/