[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Specific antidotes](https://durgical.com/en/pharmacology/classes/specific-antidotes/) › Fomepizole

[Pharmacology](https://durgical.com/en/pharmacology/) · [Specific antidotes](https://durgical.com/en/pharmacology/classes/specific-antidotes/)

# Fomepizole

Blocks alcohol dehydrogenase so methanol and ethylene glycol are not turned into their toxic acids. Ethanol is the older alternative.

Updated 2026-11-01

- Class: [Specific antidotes](https://durgical.com/en/pharmacology/classes/specific-antidotes/)
- Enzyme: Alcohol dehydrogenase
- ATC code: V03AB34
- WHO Model List of Essential Medicines

Also called: 4-methylpyrazole

✂**Alcohol dehydrogenase**Fomepizole

ⓘ The figure shows human β1 alcohol dehydrogenase with NAD⁺ and 4-iodopyrazole, a close relative of fomepizole that occupies the same site next to the zinc.

**Target in 3D:** Alcohol dehydrogenase. PDB structure 1DEH (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/1DEH) · Drag to rotate · pinch to zoom

## Mechanism of action

Methanol and ethylene glycol are not very toxic themselves; alcohol dehydrogenase starts their conversion to formic acid (methanol) or glycolic and oxalic acids (ethylene glycol), which cause metabolic acidosis, blindness and kidney failure. Fomepizole is a competitive inhibitor of alcohol dehydrogenase, so the parent alcohol is left to be removed slowly or by haemodialysis. Ethanol does the same by competing as a preferred substrate.

- Methanol or ethylene glycol reach the liver
- Fomepizole blocks alcohol dehydrogenase
- No formic, glycolic or oxalic acid is formed
- The parent alcohol is removed by dialysis or slowly

## Pharmacokinetics

**Distribution**
Distributes rapidly into total body water

**Metabolism**
Liver, mainly to 4-carboxypyrazole; with repeated doses it induces its own metabolism after about a day and a half

**Elimination**
Metabolites in urine; it is removed by haemodialysis, so dosing changes during dialysis

## Indications

- Methanol poisoning, alone or with haemodialysis (including adulterated alcoholic drinks, still seen in Colombia) [Methanol poisoning →](https://durgical.com/en/conditions/methanol-poisoning/)
- Ethylene glycol (antifreeze) poisoning, confirmed or suspected [Ethylene glycol poisoning →](https://durgical.com/en/conditions/ethylene-glycol-poisoning/)

## Adverse effects

### Common

- Headache
- Nausea
- Dizziness, drowsiness and a metallic or bad taste
- Mild rash and eosinophilia

### Serious (rare, important)

- Venous irritation and phlebosclerosis if given undiluted or as a bolus
- Allergic reactions

## Contraindications

- Documented serious hypersensitivity to fomepizole or other pyrazoles

## Key interactions

**Ethanol**
Mutual inhibition: each slows the elimination of the other

## What is monitored

- Arterial blood gases, anion gap and osmolal gap
- Methanol or ethylene glycol levels when available
- Kidney function and calcium (ethylene glycol)
- Vision (methanol)

## Administration and safety

- Always diluted and infused slowly; never as an undiluted bolus
- Polycarbonate syringes and needles are not used, because the drug damages them
- It melts at about 25 °C, so it may be solid in the vial and is liquefied before use
- Dosing is adjusted around haemodialysis sessions

## Nursing care

- Record when the alcohol was drunk and what product it was
- Check the infusion site for irritation
- Follow acid-base tests and coordinate with the dialysis team
- Assess visual acuity and report any change
- In outbreaks, report to public health so others who drank the same product are found

## Pregnancy and breastfeeding

No animal or human reproduction studies exist; it is given in pregnancy only when clearly needed, as untreated toxic alcohol poisoning is life-threatening.

## Memory aid

Fomepizole Freezes the ADH door: methanol and ethylene glycol wait outside as harmless alcohols until dialysis takes them away.

## Test yourself

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

## Why are methanol and ethylene glycol toxic?

Their metabolites are: formic acid from methanol, and glycolic and oxalic acids from ethylene glycol.

## What enzyme does fomepizole inhibit?

Alcohol dehydrogenase, competitively.

## What is the traditional alternative when fomepizole is not available?

Ethanol, which competes for alcohol dehydrogenase; it needs close monitoring of blood alcohol and glucose.

## What happens to fomepizole elimination during haemodialysis?

It is dialysed, so doses are adjusted around dialysis.

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## Related conditions

- [Methanol poisoning](https://durgical.com/en/conditions/methanol-poisoning/)
- [Ethylene glycol poisoning](https://durgical.com/en/conditions/ethylene-glycol-poisoning/)

[← Back to the class: Specific antidotes](https://durgical.com/en/pharmacology/classes/specific-antidotes/)

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 - FOMEPIZOLE injection, solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=256910fe-91f2-48f6-b0b4-55edc52dacd4) (DailyMed (U.S. National Library of Medicine), 2026); [Guía para el Manejo de Emergencias Toxicológicas](https://minsalud.gov.co/sites/rid/Lists/BibliotecaDigital/RIDE/DE/GT/guias-manejo-emergencias-toxicologicas-outpout.pdf) (Ministerio de Salud y Protección Social; Organización Panamericana de la Salud, 2017); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025); [RCSB PDB - 1DEH: CRYSTALLIZATION OF HUMAN BETA1 ALCOHOL DEHYDROGENASE (15 MG/ML) IN 50 MM SODIUM PHOSPHATE (PH 7.5), 2.0 MM NAD+ AND 1 MM 4-IODOPYRAZOLE AT 25 OC, 13% (W/V) PEG 8000](https://www.rcsb.org/structure/1DEH) (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.

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