Fomepizole (4-methylpyrazole) !

An alcohol dehydrogenase inhibitor: it stops methanol and ethylene glycol from being turned into their toxic acids.

Updated 2026-11-01

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Key facts

A potent competitive inhibitor of alcohol dehydrogenase; it also inhibits CYP2E1.
Antidote of choice in methanol and ethylene glycol poisoning: the unchanged toxin leaves through the kidney, breath or dialysis.
Compared with ethanol as an antidote: it does not intoxicate, does not cause hypoglycaemia and needs less close level monitoring.
It does not undo damage already done: it does not remove formic acid or oxalate already formed.

It is combined with haemodialysis when there is severe acidosis, visual or kidney damage, or very high levels.
The CYP2E1 3D structure (3E4E) shows 4-methylpyrazole bound to the haem iron.
Dose and duration are set by the poison centre.

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Which enzyme does fomepizole block?

Alcohol dehydrogenase (and to a lesser degree CYP2E1).

Why is fomepizole not enough once methanol has caused severe acidosis?

Because it does not remove formic acid already formed; haemodialysis is needed.

What advantage does fomepizole have over ethanol as an antidote?

It causes no intoxication or hypoglycaemia and its effect is more predictable.

Molecules are shown in their neutral form, as the databases deposit them; in the cell the acids and phosphates are ionised.

Educational information, not medical advice. For any symptom, see a health professional.

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Representative model, for educational purposes only.