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
Enzyme: Alcohol dehydrogenase
ATC code: V03AB34
WHO Model List of Essential Medicines

Also called: 4-methylpyrazole

Alcohol dehydrogenaseFomepizole

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

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 →
Ethylene glycol (antifreeze) poisoning, confirmed or suspected Ethylene glycol poisoning →

Adverse effects

Common

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

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.

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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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 (DailyMed (U.S. National Library of Medicine), 2026); Guía para el Manejo de Emergencias Toxicológicas (Ministerio de Salud y Protección Social; Organización Panamericana de la Salud, 2017); eEML - Electronic Essential Medicines List (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 (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.