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Antidotes & Toxicology Pregnancy: Use if benefit outweighs risk — methanol/ethylene glycol poisoning is life-threatening; teratogenicity data limited

Fomepizole

Brand names: Antizol

Adult dose

Dose: 15 mg/kg loading then 10 mg/kg every 12 hours for 4 doses, then 15 mg/kg every 12 hours
Route: IV
Frequency: Every 12 hours
Max: 15 mg/kg per dose
Dilute in 100 mL sodium chloride 0.9% or glucose 5%; infuse over 30 minutes. During haemodialysis: give every 4 hours

Paediatric dose

Dose: 15 mg/kg loading mg/kg
Route: IV
Frequency: Every 12 hours
Max: 15 mg/kg
Same dosing schedule as adult; seek specialist opinion in children under 2 years

Dose adjustments

Renal

Increase frequency during haemodialysis — dialysis removes fomepizole; give dose at start and every 4 hours during dialysis

Hepatic

No specific adjustment; use with caution — alcohol dehydrogenase activity may be altered

Paediatric weight-based calculator

Same dosing schedule as adult; seek specialist opinion in children under 2 years

Clinical pearls

  • Mechanism: competitive inhibitor of alcohol dehydrogenase — prevents conversion of methanol to formaldehyde and ethylene glycol to glycolate/oxalate, which cause the toxic effects
  • Indications: confirmed or strongly suspected methanol or ethylene glycol poisoning with plasma concentration above 20 mg/dL (methanol) or 50 mg/dL (ethylene glycol), metabolic acidosis, or high anion gap
  • Advantages over ethanol: predictable kinetics, no CNS depression, no hypoglycaemia, no monitoring of blood alcohol levels required — preferred first-line antidote where available
  • Haemodialysis indications: severe metabolic acidosis (pH under 7.1), renal failure, visual symptoms (methanol), very high plasma concentrations — fomepizole does NOT replace haemodialysis in severe cases
  • MHRA: fomepizole licensed in UK for ethylene glycol poisoning; methanol is off-label but supported by NPIS and toxicology guidelines — always contact NPIS (0344 892 0111)
  • Give empirically if strongly suspected — do not wait for plasma methanol/ethylene glycol levels before starting treatment

Contraindications

  • Known hypersensitivity to fomepizole or other pyrazoles
  • Do not delay haemodialysis if indicated — fomepizole is adjunct, not replacement

Side effects

  • Headache (most common)
  • Nausea
  • Dizziness
  • Phlebitis at injection site
  • Transient aminotransferase elevation
  • Eosinophilia

Interactions

  • Ethanol (mutual inhibition of metabolism — ethanol also inhibits alcohol dehydrogenase)
  • No significant drug interactions identified

Monitoring

  • Plasma methanol or ethylene glycol concentrations
  • Arterial blood gas and pH
  • Serum osmolality and osmol gap
  • Anion gap
  • Renal function and urine output
  • Visual acuity (methanol — optic nerve toxicity)

Reference: BNFc; BNF 90; NPIS Toxbase; Clinical Toxicology 2002;40(4):415-446; Pediatrics 1999;104(1):31-38. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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