Toxic Alcohols — Fomepizole and Dialysis

Key Points

• Do not wait for a send-out methanol or ethylene glycol level when the clinical probability is high and dangerous metabolism is ongoing.
• Interpret osmolar and anion gaps dynamically; either can be normal depending on timing.
• Fomepizole prevents formation of toxic metabolites but does not remove metabolites already present.
• Severe acidosis, visual toxicity, coma, seizure, renal failure, or high toxin concentrations support urgent hemodialysis.
• Methanol preferentially injures the optic system; ethylene glycol preferentially causes renal and calcium-related complications.
• Urine calcium oxalate crystals are supportive but not required for ethylene glycol diagnosis.
• Continue and adjust fomepizole during dialysis because dialysis removes the antidote as well as the toxin.
• Poison-center or medical-toxicology consultation should occur early.

Algorithm

1. Stabilize airway, breathing, circulation, mental status, and glucose.
2. Obtain electrolytes, measured osmolality, blood gas, renal function, calcium, lactate, ECG, ethanol concentration, and specific toxin levels when available.
3. Calculate anion and osmolar gaps and interpret them according to time since exposure.
4. Start fomepizole immediately when a clinically significant methanol or ethylene glycol ingestion is suspected.
5. Correct severe acidosis with bicarbonate and provide methanol or ethylene-glycol specific cofactors.
6. Contact toxicology and nephrology early and apply EXTRIP criteria for extracorporeal treatment.
7. Perform intermittent hemodialysis for severe poisoning and increase fomepizole dosing frequency during dialysis per protocol.
8. Continue monitoring until acid-base status is stable and toxin and metabolite burden are adequately cleared.

Clinical Synopsis & Reasoning

Methanol and ethylene glycol are parent alcohols whose major toxicity results from alcohol dehydrogenase metabolism. Methanol is converted to formic acid, producing optic nerve and basal ganglia injury. Ethylene glycol is converted to glycolic and oxalic acids, causing acidosis, hypocalcemia, and acute kidney injury from calcium oxalate deposition. Early after ingestion, patients may appear intoxicated with an osmolar gap before substantial acidosis develops. As metabolites accumulate, the osmolar gap may fall while the anion gap rises.

A normal osmolar gap does not exclude late toxic alcohol poisoning, and an elevated osmolar gap is not specific. Calculate both gaps while obtaining a measured serum osmolality, electrolytes, blood gas, lactate, glucose, renal function, calcium, and toxin concentrations when available. False lactate elevation can occur on some point-of-care analyzers in ethylene glycol poisoning because glycolate interferes with the assay. Urinary calcium oxalate crystals support ethylene glycol exposure but are neither required nor sufficiently sensitive to rule it out.

Clinical clues for methanol include blurred or snowy vision, photophobia, visual-field abnormalities, abdominal symptoms, and severe acidosis. Ethylene glycol can present with intoxication followed by cardiopulmonary and renal manifestations. Isopropanol produces ketosis and osmolar-gap elevation without the same high-anion-gap acidosis because acetone is the main metabolite. Prompt toxicology consultation is appropriate whenever the diagnosis is plausible because delayed antidote therapy allows additional toxic metabolite formation.

Treatment Strategy & Disposition

Fomepizole inhibits alcohol dehydrogenase and is the preferred antidote for methanol and ethylene glycol poisoning. A common adult regimen is 15 mg/kg IV loading followed by 10 mg/kg every 12 hours for four doses, then 15 mg/kg every 12 hours, with increased dosing frequency during hemodialysis according to protocol. Start treatment when a significant ingestion is strongly suspected, the concentration meets treatment criteria, or compatible acidosis and osmolar findings make delay unsafe. Ethanol is an alternative alcohol dehydrogenase substrate when fomepizole is unavailable but is harder to titrate and causes more adverse effects.

Treat severe metabolic acidosis with sodium bicarbonate while arranging definitive therapy. Give folinic acid or folic acid in methanol poisoning to support formate metabolism. Give thiamine and pyridoxine in ethylene glycol poisoning to favor nontoxic metabolic pathways. Correct symptomatic hypocalcemia, but do not give calcium solely to normalize an asymptomatic laboratory value because additional calcium oxalate precipitation is a theoretical concern.

Intermittent hemodialysis rapidly removes parent alcohol and toxic metabolites and corrects acidosis. EXTRIP recommendations support dialysis in severe methanol or ethylene glycol poisoning based on clinical findings such as coma, seizure, visual toxicity, severe acidosis, kidney failure, and toxin concentration thresholds, with exact triggers influenced by whether fomepizole is being used. Continue fomepizole during dialysis with adjusted dosing. Admit treated patients to a monitored setting and follow acid-base status, electrolytes, organ function, and toxin concentration until the poison has been cleared and metabolism is controlled.

Epidemiology / Risk Factors

• Exposure may be accidental, occupational, recreational, or intentional and can involve antifreeze, windshield-washer fluid, solvents, fuels, or improperly produced alcohol.
• Children are at risk from accidental ingestion of household products stored in accessible or unlabeled containers.
• Outbreaks of methanol poisoning occur when illicit or contaminated alcohol is consumed.
• Coingested ethanol can delay symptom onset by competitively inhibiting alcohol dehydrogenase.
• Patients with intentional ingestion require mental-health assessment once medically stabilized.

Investigations

Cofactor Therapy

Pharmacology

Prognosis / Complications

• Early antidote treatment before severe acidosis or organ injury is associated with excellent outcomes in many patients.
• Methanol-related blindness and basal ganglia injury can be permanent when treatment is delayed.
• Ethylene glycol can cause severe acute kidney injury requiring temporary dialysis, and renal recovery may take weeks.
• Severe acidemia, coma, seizure, and delayed presentation are associated with worse outcomes.
• Dialysis plus fomepizole markedly improves clearance and physiologic correction in severe cases.

Patient Education / Counseling

• Emphasize safe storage of antifreeze, solvents, and alcohol-containing chemicals in original labeled containers and away from children.
• Never transfer toxic alcohol products into beverage bottles or food containers.
• Patients treated for methanol should receive follow-up for visual symptoms and neurologic sequelae.
• Patients with ethylene glycol-associated kidney injury require renal follow-up until creatinine and urine output recover.
• Any future suspected ingestion should prompt immediate poison-center contact rather than waiting for symptoms.
• Intentional ingestion requires a suicide-risk assessment and safe-disposition planning after medical stabilization.

Notes

Toxic alcohol interpretation is a timing problem. Early after ingestion the parent alcohol can raise the osmolar gap before much anion-gap acidosis exists; later, metabolism may produce profound acidosis after the osmolar gap has narrowed.

EXTRIP provides toxin-specific extracorporeal-treatment criteria and should be used with toxicology consultation rather than relying on a memorized single concentration threshold.

References

1. EXTRIP Workgroup Methanol Recommendations — Link
2. EXTRIP Workgroup Ethylene Glycol Recommendations — Link