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Toxic alcohols: methanol and ethylene glycol
Methanol and ethylene glycol are not toxic themselves — their metabolites, formed by alcohol dehydrogenase, cause severe acidosis, blindness (methanol) and kidney failure (ethylene glycol); so the enzyme is blocked with fomepizole and the toxin is removed by dialysis.
Why it matters in the exam
The classic question describes metabolic acidosis with a raised anion gap together with a raised osmolar gap, sometimes after drinking a cleaning fluid, car coolant or counterfeit alcohol. Methanol shows as blurred vision and "vision like a snowfield", and ethylene glycol as kidney injury with calcium oxalate crystals in the urine.
The correct answer is fomepizole (15 mg/kg loading, then 10 mg/kg every 12 hours) or ethanol as an alternative, bicarbonate for acidosis, and vitamins as adjuncts: folic or folinic acid for methanol, thiamine and pyridoxine for ethylene glycol. A common distractor is waiting for a blood level before giving fomepizole — when suspicion is high, start at once.
The change over time is also asked: early on the osmolar gap is high and the anion gap almost normal, and later the osmolar gap falls and the anion gap rises — so a normal osmolar gap does not exclude a late poisoning. Isopropanol is different: it causes ketosis without acidosis and an osmolar gap, and does not need fomepizole. Dialysis indications include severe acidosis, visual disturbance, seizures or coma, kidney failure and high toxin levels.
Key points
- Anion gap acidosis with an osmolar gap — think of methanol and ethylene glycol.
- Methanol — eyes; ethylene glycol — kidneys and oxalate.
- Fomepizole 15 mg/kg loading and 10 mg/kg every 12 hours.
- Dialysis for severe acidosis, visual damage, coma or kidney failure.
- Vitamins help: folinic acid for methanol, thiamine and pyridoxine for ethylene glycol.
Summary table
| Substance | Toxic metabolite | Main injury | Additional treatment |
|---|---|---|---|
| Methanol | Formic acid | Optic nerve and basal ganglia | Fomepizole, folinic acid, dialysis |
| Ethylene glycol | Glycolic acid and oxalate | Kidneys, hypocalcaemia | Fomepizole, thiamine and pyridoxine, dialysis |
| Isopropanol | Acetone | Central depression, ketosis without acidosis | Supportive care only |
| Ethanol | Acetaldehyde | Intoxication, hypoglycaemia | Supportive care, thiamine |
A free exam question
מטופל כבן 50 , מחוסר הכרה, .מגיע למלר"ד במראה מוזנח, נראה חסר בית לאחר ייצוב ראשוני, חוזרות התשובות הבאות בבדיקת הגזים: measured pH 7.12 pCO2 27 Na+ 140 K+ 3.3 Cl- 104 Glu 72 Lac 2 HCO3std 12 Cr 1.6 מה מהבאים יכולה להיות הסיבה למצבו? (the question as examined, in Hebrew)
- א. שתיית אלכוהול
- ב. שלשולים מרובים
- ג. משבר אדיסוני (Addison crisis)
- ד. Fanconi's syndrome
In the full version for subscribers
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Sources
- Goldfrank's Toxicologic Emergencies, 11th edition (2019) — Toxic alcohols
- EXTRIP workgroup, Extracorporeal treatment for methanol poisoning (Critical Care Medicine), 2015 — Recommendations
- Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 9th edition (2020) — Alcohols
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.