Early ethylene glycol poisoning — MRCEM SBA MCQ

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EasyToxicology and environmental emergenciesEarly ethylene glycol poisoningMRCEM SBA

A 37-year-old man attends the emergency department 90 minutes after his partner witnessed him drink approximately 70 mL of antifreeze labelled as containing ethylene glycol. He is mildly ataxic but alert, haemodynamically stable and protecting his airway. Plasma ethanol is undetectable. Measured serum osmolality is 330 mOsm/kg and calculated osmolality is 290 mOsm/kg. Venous pH is 7.39, the anion gap is 12 mmol/L and creatinine is 82 µmol/L. A sample has been sent for ethylene glycol measurement, but the result will be delayed. Following initial assessment and discussion with the National Poisons Information Service, which treatment should be started now?

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Correct answer: A — Commence intravenous fomepizole

The witnessed ingestion, early ataxia and 40 mOsm/kg osmolal gap support significant ethylene glycol exposure. A normal pH and anion gap at 90 minutes are not reassuring: unmetabolised ethylene glycol raises the osmolal gap before acidic metabolites accumulate. ([southtees.nhs.uk](https://www.southtees.nhs.uk/services/pathology/tests/ethylene-glycol/)) **A is best:** start fomepizole now rather than await the assay. It inhibits formation of toxic metabolites, and UK product information advises starting treatment as soon as poisoning is suspected, even without signs of toxicity. The patient needs admission for serial clinical, acid–base and renal assessment. ([medicines.org.uk](https://www.medicines.org.uk/emc/product/101333/smpc)) **B** is tempting because renal function and acid–base status are currently normal, but observation without an antidote risks allowing toxicity to develop. **C** also inhibits ethylene glycol metabolism, but fomepizole is the UK antidote of choice when available; ethanol is an alternative if it cannot be obtained. ([bedsformulary.nhs.uk](https://www.bedsformulary.nhs.uk/docs/L%26D%20ANTIDOTES%20POSTER%20MASTER-%20%28Oct%202022%29%20Final.pdf?UID=974099898202532325915)) **D** can be necessary in severe poisoning, but this patient has neither severe clinical features nor biochemical findings that establish an immediate need for dialysis; reassess if his condition or results change. ([pubmed.ncbi.nlm.nih.gov](https://pubmed.ncbi.nlm.nih.gov/36765419/)) **E** does not address this ingestion because activated charcoal does not adsorb appreciable quantities of ethylene glycol. ([assets.publishing.service.gov.uk](https://assets.publishing.service.gov.uk/media/6711140ce94bb9726918ed86/incident-management-ethylene-glycol.pdf))

Reference: Fomepizole Waymade 1 g/ml concentrate for solution for infusion: Summary of Product Characteristics (September 2025) — https://www.medicines.org.uk/emc/product/101333/smpc Ethylene Glycol (Date not stated on the checked page) — https://www.southtees.nhs.uk/services/pathology/tests/ethylene-glycol/ Antidotes poster (October 2022) — https://www.bedsformulary.nhs.uk/docs/L%26D%20ANTIDOTES%20POSTER%20MASTER-%20%28Oct%202022%29%20Final.pdf?UID=974099898202532325915