Methanol (methyl alcohol) is a toxic alcohol found in windshield-washer fluid, solvents, and adulterated spirits whose toxicity is driven by its metabolite formic acid, causing severe high anion-gap metabolic acidosis, blindness, and death if not rapidly treated. The following figure illustrates the metabolic pathway and mechanism of fomepizole's action in blocking formic acid production:
1. History
- Key HPI questions: What substance was ingested? How much? When? Was it intentional or accidental? Any co-ingestion of ethanol (delays symptom onset by 72–96 hours)? [2]
- Symptom characterization: Initial inebriation → latent period (6–24 hours without ethanol co-ingestion) → headache, nausea, vomiting, abdominal pain, blurred vision progressing to blindness [2-3]
- Sources of exposure: Windshield-washer fluid, carburetor cleaner, racing fuels, camp stove fuel, adulterated "moonshine," methanol-containing hand sanitizers [2][4]
- Important negatives: Ask about ethanol co-ingestion (delays metabolism and symptom onset), suicidal intent, occupational/industrial exposure
2. Alarm Features
- Visual complaints — any blurred vision, scotomata, or blindness (formate-mediated optic nerve toxicity); present in 29–72% of cases [2]
- Severe metabolic acidosis (pH ≤ 7.15) [5]
- Altered mental status, seizures, or coma
- Hemodynamic instability or respiratory failure (Kussmaul breathing)
- An anion gap ≥ 28 at presentation independently predicts poor neurologic outcome — no patient with this threshold had favorable recovery in one cohort [6]
3. Medications
- Antidotes:
- Fomepizole (first-line) — loading dose 15 mg/kg IV, then 10 mg/kg q12h × 4 doses, then 15 mg/kg q12h; increase to q4h during hemodialysis [2][7]
- IV ethanol (alternative if fomepizole unavailable) — target serum ethanol 100 mg/dL; requires ICU monitoring and frequent level checks [2]
- Adjuncts:
- Folic acid 1 mg/kg IV q4–6h (promotes conversion of formic acid → CO₂ + H₂O) [2]
- Sodium bicarbonate IV for acidosis correction; increases formate ionization and urinary excretion, reduces optic nerve penetration [2]
- Caution: Do NOT use polycarbonate syringes/needles with fomepizole (drug interaction with polycarbonate material) [7]
- Gastric decontamination is generally not helpful due to rapid GI absorption [2]
4. Diet
- Not directly applicable in the acute setting
- In mass-poisoning outbreaks, public health messaging should emphasize never ingesting non-beverage alcohol products, hand sanitizers, or unregulated spirits [4]
5. Review of Systems
- Neuro: Headache, confusion, obtundation, seizures, Parkinson-like features (rare, late) [2]
- Ophthalmologic: Blurred vision, photophobia, scotomata, complete vision loss
- GI: Nausea, vomiting, abdominal pain (often epigastric)
- Respiratory: Dyspnea, tachypnea/Kussmaul breathing (compensatory for acidosis)
- Psychiatric: Suicidal ideation (intentional ingestion)
6. Collateral History and Family History
- Collateral from EMS, family, or bystanders is critical: what product was ingested, how much, when, any co-ingestants
- Alcohol use disorder history — patients with AUD may ingest non-beverage alcohols as ethanol substitutes [4]
- Occupational exposure (industrial solvents, fuel handling)
- Family history is generally not relevant to acute toxicity
7. Risk Factors
- Alcohol use disorder (most common risk factor for intentional or substitution ingestion) [4]
- Occupational exposure to industrial solvents
- Consumption of illicitly distilled spirits ("moonshine") or adulterated alcohol — a major cause of mass outbreaks globally [2]
- Suicidal intent
- Pediatric accidental ingestion
- Use of methanol-containing hand sanitizers (reported during COVID-19 pandemic) [4]
8. Differential Diagnosis
- Ethylene glycol poisoning — distinguished by calcium oxalate crystalluria, AKI, hypocalcemia; no visual symptoms [2]
- Isopropanol poisoning — elevated osmolal gap but NO anion-gap acidosis; acetonemia/ketonuria; no visual changes [2]
- Diabetic ketoacidosis — elevated anion gap + osmolal gap; check glucose, ketones
- Alcoholic ketoacidosis — history of chronic ethanol use, starvation
- Lactic acidosis (sepsis, shock, metformin toxicity)
- Salicylate toxicity — mixed respiratory alkalosis and metabolic acidosis; tinnitus
- Uremia/CKD — elevated BUN/Cr, chronic history
- Key distinguishing feature of methanol: Visual complaints + high anion-gap metabolic acidosis + elevated osmolal gap is the classic triad [2][8]
9. Past Medical History
- Prior toxic alcohol ingestion episodes
- Alcohol use disorder or substance use history
- Psychiatric history (depression, prior suicide attempts)
- Baseline renal function (impaired kidney function is an indication for hemodialysis) [5]
- Hepatic disease (may alter metabolism)
10. Physical Exam
- Vitals: Tachycardia, tachypnea (Kussmaul breathing), hypotension (late/severe)
- Neuro: Altered mental status ranging from mild confusion to coma; GCS assessment is critical (lower GCS predicts poor outcome) [6]
- Eyes: Dilated or sluggish pupils, decreased visual acuity, afferent pupillary defect, fundoscopic exam may show optic disc hyperemia/edema
- Abdomen: Epigastric tenderness
- Respiratory: Deep, rapid breathing pattern
- Skin: May appear flushed; assess for signs of co-ingestion
11. Lab Studies
Key pearl: The osmolal gap and anion gap evolve inversely over time — early presentation shows high osmolal gap (unmetabolized methanol) with normal anion gap; late presentation shows high anion gap (formate accumulation) with normalizing osmolal gap. A normal osmolal gap does NOT rule out methanol poisoning. [2][9]
12. Imaging
- CT head: Indicated for altered mental status or coma; may show basal ganglia hemorrhage or necrosis (putaminal hemorrhage is characteristic of severe methanol poisoning) [6]
- MRI brain: More sensitive for detecting basal ganglia necrosis, subcortical white matter involvement, and restricted diffusion — findings specific to methanol (not seen with other toxic alcohols) [6]
- Imaging is not required for diagnosis but is important for prognostication in severe cases
13. Special Tests
Estimated osmolality = (2 × Na) + (BUN/2.8) + (glucose/18)
Osmolal gap = measured osmolality − estimated osmolality
Normal: <10 mOsm/kg; each 10 mg/dL methanol raises osmolality by ~3.09 mOsm/kg [2]
- Anion gap calculation: Na − (Cl + HCO₃); albumin-corrected AG may improve prognostic accuracy (ACAG ≥ 25.6 predicts poor outcome) [11]
- Gas chromatography / liquid chromatography — gold standard for methanol quantification but often unavailable or delayed [2-3]
- Point-of-care testing: Formate assays under development but not widely available [3]
- Wood's lamp urine exam — fluorescein in antifreeze may fluoresce (ethylene glycol, not methanol)
14. ECG
- Obtain ECG to assess for dysrhythmias secondary to severe acidosis
- Look for QT prolongation, wide-complex tachycardia, or bradycardia in critically ill patients
- No pathognomonic ECG findings for methanol specifically, but severe acidemia can cause life-threatening arrhythmias
15. Assessment
Methanol toxicity is a time-critical diagnosis. The parent compound is relatively nontoxic; morbidity and mortality result from its metabolite formic acid, which causes optic nerve toxicity (blindness) and profound metabolic acidosis with secondary lactic acidosis via mitochondrial inhibition ("circulus hypoxicus"). [3][10] Symptoms typically appear 6–24 hours post-ingestion but may be delayed up to 72–96 hours with ethanol co-ingestion. [2] Mortality in treated patients remains 17–36% depending on severity and timing of treatment. [2][11] Survivors may have permanent visual impairment or basal ganglia necrosis with Parkinson-like features. [2][6]
The following algorithm from the NEJM provides a practical decision framework for diagnosis and management:
16. Treatment Plan
Initial stabilization
- ABCs; intubate if GCS is severely depressed
- IV access, continuous monitoring
- Aggressive IV sodium bicarbonate for pH < 7.3 (corrects acidosis, reduces formate CNS penetration) [2]
Antidotal therapy — initiate immediately upon suspicion (do not wait for confirmatory levels): [7]
- Fomepizole (preferred): 15 mg/kg IV loading → 10 mg/kg q12h × 4 doses → 15 mg/kg q12h thereafter; dose q4h during hemodialysis [2][7]
- IV ethanol (if fomepizole unavailable): target serum ethanol 100 mg/dL; requires ICU-level monitoring [2]
- Folic acid 1 mg/kg IV q4–6h (enhances formate metabolism) [2]
Hemodialysis indications (per EXTRIP consensus): [5]
- Coma, seizures, or new vision deficits
- pH ≤ 7.15 or persistent acidosis despite treatment
- Anion gap > 24 mmol/L
- Methanol level > 50 mg/dL (or >70 mg/dL with fomepizole, >60 mg/dL with ethanol)
- Impaired kidney function
- Intermittent HD is preferred over CVVHD/HDF (methanol t½ 3.7h vs 8.1h) [12]
- Continue fomepizole and folic acid during HD [5]
- Terminate HD when methanol < 20 mg/dL (200 mg/L) with clinical improvement [5]
- Avoid systemic anticoagulation during HD (risk of intracerebral hemorrhage) [5]
Discontinue fomepizole when methanol is undetectable or < 20 mg/dL AND patient is asymptomatic with normal pH [7]
17. Disposition
- ICU admission: All patients with significant metabolic acidosis, visual symptoms, altered mental status, or requiring hemodialysis or IV ethanol infusion [2]
- Monitored bed: Patients with confirmed ingestion, mild symptoms, and adequate ADH blockade with fomepizole (may not require ICU if fomepizole is used) [2]
- Consult early: Toxicology/Poison Control, Nephrology (for HD), Ophthalmology (for visual complaints)
- Discharge criteria: Methanol undetectable or < 20 mg/dL, normal pH, asymptomatic, no visual complaints, psychiatric clearance if intentional ingestion [7]
- Fomepizole alone (without HD) prolongs elimination half-life to ~71 hours, which may extend hospitalization significantly [2]
18. Follow Up / Return Precautions
- Ophthalmology follow-up within 1–2 weeks for all patients with any visual complaints; permanent vision loss is possible even after treatment [2][4]
- Neurology follow-up if any neurologic deficits; delayed Parkinson-like features can emerge days to weeks after exposure [2]
- Psychiatry follow-up for intentional ingestions
- Return precautions: Return immediately for any new or worsening visual changes, confusion, headache, abdominal pain, or difficulty breathing
- Expected course: With early treatment (before significant formate accumulation), full recovery is expected. Late presentation with severe acidosis carries high morbidity and mortality [6][13]
- Patient counseling: Never ingest non-beverage alcohol products; avoid unregulated spirits; if alcohol use disorder is present, refer to addiction services
References
1. Fomepizole for Ethylene Glycol and Methanol Poisoning. — Brent J. The New England Journal of Medicine. 2009.
2. Toxic Alcohols. — Kraut JA, Mullins ME. The New England Journal of Medicine. 2018.
3. Approach to the Treatment of Methanol Intoxication. — Kraut JA. American Journal of Kidney Diseases : The Official Journal of the National Kidney Foundation. 2016.
4. Serious Adverse Health Events, Including Death, Associated With Ingesting Alcohol-Based Hand Sanitizers Containing Methanol - Arizona and New Mexico, May-June 2020. — Yip L, Bixler D, Brooks DE, et al. MMWR. Morbidity and Mortality Weekly Report. 2020.
5. Recommendations for the Role of Extracorporeal Treatments in the Management of Acute Methanol Poisoning: A Systematic Review and Consensus Statement. — Roberts DM, Yates C, Megarbane B, et al. Critical Care Medicine. 2015.
6. Neurologic Complications in Critically Ill Patients With Toxic Alcohol Poisoning: A Multicenter Population-Based Cohort Study. — AlSamh DA, Kramer AH. Neurocritical Care. 2024.
7. FDA Drug Label. — Updated date: 2023-10-26. Food and Drug Administration.
8. High Risk and Low Prevalence Diseases: Toxic Alcohol Ingestion. — Inman B, Maddry JK, Ng PC, Koyfman A, Long B. The American Journal of Emergency Medicine. 2023.
9. Anion and Osmolal Gaps in the Diagnosis of Methanol Poisoning: Clinical Study in 28 Patients. — Hovda KE, Hunderi OH, Rudberg N, Froyshov S, Jacobsen D. Intensive Care Medicine. 2004.
10. The Hypothesis of Circulus Hypoxicus and Its Clinical Relevance in Patients With Methanol Poisoning - An Observational Study of 35 Patients. — Drangsholt E, Vangstad M, Zakharov S, Hovda KE, Jacobsen D. Basic & Clinical Pharmacology & Toxicology. 2018.
11. Lactate-to-Albumin Ratio and Albumin-Corrected Anion Gap as Predictors of Outcome in Methanol Poisoning: A Retrospective Observational Study. — Ağaçkıran İ, Ağaçkıran M. L PloS One. 2025.
12. Intermittent Hemodialysis Is Superior to Continuous Veno-Venous Hemodialysis/Hemodiafiltration to Eliminate Methanol and Formate During Treatment for Methanol Poisoning. — Zakharov S, Pelclova D, Navratil T, et al. Kidney International. 2014.
13. Current Recommendations for Treatment of Severe Toxic Alcohol Poisonings. — Mégarbane B, Borron SW, Baud FJ. Intensive Care Medicine. 2005.