Toxicology & Substance Use · Topic 5 of 17

Toxic Alcohols

Toxicology · methanol and ethylene glycol

Toxic Alcohols

An osmolar gap that becomes an anion gap: block alcohol dehydrogenase with fomepizole on suspicion and dialyze for end-organ toxicity or severe acidosis.

Key numbers

Osmolar gap over 10 suggests toxic alcoholOsm gap > 10

Fomepizole 15 mg/kg IV on suspicionFomepizole 15 mg/kg

01 · CalculateOsmolar gap over 10 suggests toxic alcohol

Osmolar gap = measured osmolality − calculated (2 × Na⁺ + glucose/18 + BUN/2.8, plus ethanol when present); a gap above 10 with a high anion gap acidosis suggests methanol or ethylene glycol.

02 · GiveFomepizole 15 mg/kg IV on suspicion

Give fomepizole as soon as methanol or ethylene glycol is suspected: 15 mg/kg IV over 30 minutes, then 10 mg/kg every 12 hours for 4 doses, then 15 mg/kg every 12 hours.

03 · Defined byDialyze for coma, seizures, vision loss, AKI

Hemodialysis removes both the alcohol and its toxic acid: use it for severe poisoning — coma, seizures, new visual deficits, AKI, severe or persistent metabolic acidosis despite antidote — and for very high alcohol levels.

Presentation

What you'll see

Methanol: formic acid blindsMethanol (windshield washer fluid, solvents, illicit spirits) is metabolized to formic acid, which injures the optic nerve: blurred vision, photophobia and visual field loss progressing to blindness, with profound acidosis.

Ethylene glycol: oxalate crystals and AKIEthylene glycol (antifreeze) becomes glycolic and oxalic acid; calcium oxalate crystals deposit in the kidney causing AKI and in tissues causing hypocalcemia — urine crystals support the diagnosis but their absence does not exclude it.

Diagnosis & monitoring

Work-up

Stop fomepizole: level < 20 mg/dL, normal pHContinue fomepizole until the methanol or ethylene glycol level is undetectable or below 20 mg/dL and the patient is asymptomatic with a normal pH.

Methanol dialysis: pH ≤ 7.15, gap > 24EXTRIP methanol: dialyze for coma, seizures, new vision deficits, pH ≤ 7.15, persistent acidosis, anion gap > 24, kidney impairment, or methanol > 700 mg/L on fomepizole; stop at < 200 mg/L with clinical improvement.

Ethylene glycol dialysis: gap > 27 or AKIEXTRIP ethylene glycol: dialyze for coma, seizures, AKI, glycolate > 12 mmol/L or anion gap > 27; suggested for ethylene glycol > 50 mmol/L or osmolar gap > 50 on fomepizole; stop at gap < 18.

Do right now

In this order

First moves

Osmolar gap over 10 suggests toxic alcoholOsm gap > 10

→

Fomepizole 15 mg/kg IV on suspicionFomepizole 15 mg/kg

→

Add folic or folinic acid for methanol

→

Dialyze for coma, seizures, vision loss, AKI

Why each step

Osmolar gap over 10 suggests toxic alcoholOsmolar gap = measured osmolality − calculated (2 × Na⁺ + glucose/18 + BUN/2.8, plus ethanol when present); a gap above 10 with a high anion gap acidosis suggests methanol or ethylene glycol.

Fomepizole 15 mg/kg IV on suspicionGive fomepizole as soon as methanol or ethylene glycol is suspected: 15 mg/kg IV over 30 minutes, then 10 mg/kg every 12 hours for 4 doses, then 15 mg/kg every 12 hours.

Add folic or folinic acid for methanolIn methanol poisoning, add folic or folinic acid (leucovorin) to fomepizole: folate speeds conversion of formic acid to carbon dioxide and water.

Dialyze for coma, seizures, vision loss, AKIHemodialysis removes both the alcohol and its toxic acid: use it for severe poisoning — coma, seizures, new visual deficits, AKI, severe or persistent metabolic acidosis despite antidote — and for very high alcohol levels.

Management

Orders

Ethanol infusion if fomepizole unavailableIf fomepizole is unavailable, IV ethanol competitively occupies alcohol dehydrogenase: 10% ethanol 10 mL/kg over 1 hour, then 1–2 mL/kg/h to keep blood ethanol near 100 mg/dL.

Dose fomepizole every 4 hours during dialysisFomepizole is dialyzable: dose it every 4 hours during hemodialysis and continue it afterward until stopping criteria are met, because ethylene glycol levels can rebound after dialysis.

Most labs can't measure levels quicklyMany laboratories cannot measure methanol or ethylene glycol quickly, so start fomepizole on the history, an unexplained high anion gap acidosis, an osmolar gap, visual symptoms or urine oxalate crystals.

Methanol or ethylene glycol?

Commonly confused

Common source	Windshield washer fluid, solvents, illicit spirits
Toxic acid	Formic acid
Target organ	Optic nerve — blurred vision to blindness
Antidote	Fomepizole plus folic or folinic acid
Dialysis anion gap (EXTRIP)	> 24 mmol/L

Commonly confused

Tell apart

Osmolar gap early, anion gap late must knowThe parent alcohol raises the osmolar gap early; as it is metabolized to organic acids the anion gap rises and the osmolar gap falls, so a normal osmolar gap does not exclude toxic alcohol poisoning.

Isopropanol: ketosis without acidosisIsopropanol (rubbing alcohol) is converted to acetone: deep CNS depression, hemorrhagic gastritis and an osmolar gap with ketosis but no anion gap acidosis or retinal injury; treatment is supportive.

More detail

Reference

Show 4 reference facts

Methanol toxicity has a 12–18-hour latent period because the parent alcohol is not the toxin; 60–250 mL can severely poison an adult.

Calcium oxalate crystalluria appears 4–8 hours after ethylene glycol ingestion (envelope-shaped dihydrate early, needle-shaped monohydrate later); fluorescein in some antifreeze may make urine fluoresce.

Isopropanol is about twice as intoxicating as ethanol: a level of 100 mg/dL is roughly equivalent to an ethanol level of 200 mg/dL; acetone gives a fruity breath odor.

In the EXTRIP ethylene glycol cohort, patients with glycolate ≤ 12 mmol/L (anion gap ≤ 28) had 3.6% mortality, and those given dialysis did no better than those who were not.

Pearl

Early the osmolar gap is high and the anion gap normal; as the alcohol is metabolized to acid, the gaps trade places.

Sources · Merck Manual Professional — Metabolic Acidosis (osmolar gap, toxic alcohol testing) · Fomepizole injection prescribing information — DailyMed (Zydus) · Merck Manual Professional — Table: Symptoms and Treatment of Specific Poisons (methyl and isopropyl alcohol, ethylene glycol) · Gallagher N, Edwards FJ. The Diagnosis and Management of Toxic Alcohol Poisoning in the Emergency Department: A Review Article. Adv J Emerg Med 2019 · Roberts DM et al. Recommendations for the role of extracorporeal treatments in the management of acute methanol poisoning (EXTRIP). Crit Care Med 2015;43:461–472 (abstract via Europe PMC) · Ghannoum M et al. Extracorporeal treatment for ethylene glycol poisoning: systematic review and recommendations from the EXTRIP workgroup. Crit Care 2023;27:56 · UMEM Educational Pearls (Univ. of Maryland) — Extracorporeal treatment strategies for acute methanol poisoning (EXTRIP summary; stop < 200 mg/L) · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).