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Antidotes & Toxicology Pregnancy: No clinical data in pregnant women; animal studies have shown reproductive toxicity. Should not be used during pregnancy unless clearly necessary. Advised to discontinue breastfeeding temporarily during treatment.

Fomepizole

Brand names: Antizol

Used in: Poisoning & Overdose

Fomepizole is an antidote used in the treatment of poisoning with toxic alcohols, principally ethylene glycol and methanol.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Loading dose 15 mg/kg, then 10 mg/kg every 12 hours
Route: intravenous infusion (over 30–45 minutes; must be diluted, not given as bolus)
Frequency: loading dose then every 12 hours
For suspected ethylene glycol poisoning; begin as early as possible even without signs of toxicity. Patients with normal to mild/moderate renal impairment (serum creatinine 100–265 micromol/l) not requiring haemodialysis: loading dose 15 mg/kg, then per-schedule doses every 12 hours until ethylene glycol level below 0.2 g/l (3.2 mmol/l) — SPC schedule: 15 (loading), 10 (2nd), 10 (3rd), 10 (4th), 7.5–15 (5th), 5–15 (6th) mg/kg. Severe renal impairment (serum creatinine >265 micromol/l): haemodialysis plus loading dose 15 mg/kg over 30–45 min, then 1 mg/kg/hour continuous infusion for the entire duration of haemodialysis. Monitor plasma ethylene glycol every 12–24 hours. Children: no PK data; clinical experience limited and based on similar weight-adjusted doses. Ethanol and fomepizole combination not recommended.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance, to other pyrazoles, or to any excipient

Side effects

  • Dizziness (very common)
  • Headache (very common)
  • Nausea, vomiting, diarrhoea, dyspepsia, hiccups (common)
  • Eosinophilia, anaemia (common)
  • Increased transaminases (common)

Interactions

  • Concurrent use with ethanol reduces the elimination rate of both substances — concomitant use not recommended

Clinical monograph

How it works

It inhibits alcohol dehydrogenase, blocking the metabolism of ethylene glycol and methanol into their toxic acid metabolites and allowing the parent alcohols to be cleared more safely.

Prescribing in practice

  • Start as early as possible once toxic-alcohol poisoning is suspected, before significant metabolic acidosis develops, to prevent formation of toxic metabolites.
  • Use alongside supportive care and consider haemodialysis in severe poisoning, significant acidosis or renal impairment.
  • Manage in consultation with the National Poisons Information Service, as dosing may need adjustment during dialysis.

Monitoring

Monitor acid-base status, renal function, electrolytes and, where available, toxic-alcohol concentrations during treatment.

Counselling the patient

  • Explain that this antidote stops a poison being turned into its harmful form.
  • Advise the team that dialysis may also be needed in severe cases.
  • Reassure the patient that treatment is guided by blood tests and specialist advice.

Evidence & guidelines

Fomepizole is an established antidote for ethylene glycol and methanol poisoning, used with supportive care and dialysis where indicated.

Reference: NPIS Toxbase; Clinical Toxicology 2002; 40(4):415-446; Pediatrics 1999; 104(1):31-38; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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Featured in these MRCEM clinical pathways

Fomepizole is a core drug in the following exam-focused workups on our sister siteReviseMRCEM.

MRCEM Primary / Intermediate / OSCE candidates: each pathway includes exam-style questions, RCEM/NICE citations, and FAQ summaries.