3. Toxic Alcohols (Methanol, Ethylene Glycol, Isopropanol)

Quick Recap

Toxicology System, Protocol 3/8. Covers methanol, ethylene glycol, and isopropanol — the three toxic alcohol ingestions requiring rapid ICU recognition.

1. General Diagnostic Framework

All alcohols present similarly at first: ataxia, dysarthria, somnolence, respiratory depression, characteristic breath odor — clinical exam alone cannot distinguish simple ethanol intoxication from a genuinely toxic alcohol ingestion. The key to diagnosis is maintaining a HIGH INDEX OF SUSPICION and measuring the ANION GAP and OSMOLAR GAP in any patient with an alcohol-like presentation and an unclear/unreliable history — do not assume ethanol intoxication by default.

Osmolar gap = measured osmolality − calculated osmolality; the SCREENING TEST OF CHOICE for methanol/ethylene glycol given rapid availability compared to specific serum alcohol assays. Important limitation: the osmolar gap NARROWS over time as the parent alcohol is metabolized to its toxic acid metabolites — a normal/low osmolar gap in a LATE presentation does NOT exclude toxic alcohol poisoning, since by that point the diagnostic signal has shifted from the parent compound (driving the osmolar gap) to the metabolites (driving the anion gap acidosis) — check BOTH gaps, and interpret a late presentation's normal osmolar gap in light of a persistently elevated anion gap.

CRITICAL PRINCIPLE: treatment should NOT be delayed while awaiting definitive serum alcohol level results if clinical suspicion is high (compelling history, elevated osmolar/anion gap, compatible symptoms) — fomepizole and consideration of hemodialysis should be initiated empirically, given the narrow therapeutic window before irreversible toxic metabolite-driven organ damage occurs.

2. Methanol

Sources: household solvents, ingested as an ethanol substitute, homemade spirits (sometimes ingested unknowingly).

Course: initial inebriation, followed by a characteristic LATENT PERIOD of 12+ HOURS before severe toxicity manifests — anion gap acidosis, VISUAL DISTURBANCE/BLINDNESS, respiratory failure, seizures, coma. This latent period is a critical trap — a patient who initially appears to have simple, resolving intoxication can deteriorate severely hours later once toxic metabolites accumulate.

Exam: assess pupillary light reflex AND perform funduscopic exam specifically to evaluate optic nerve injury/vision — methanol toxicity has a specific ocular target, unlike ethylene glycol.

Mechanism: methanol -> formaldehyde -> formate (via alcohol dehydrogenase) — formate is the toxic metabolite responsible for both the metabolic acidosis and the optic nerve toxicity.

Diagnosis: osmolar gap as screening (Section 1); definitive serum methanol level, though LATE presentations may show an UNDETECTABLE methanol level with an ELEVATED FORMATE level (the parent compound has already been fully metabolized) — a low/negative methanol level does NOT exclude the diagnosis in a delayed presentation with a compatible clinical picture and acidosis.

3. Ethylene Glycol

Sources: antifreeze and other solvents; ingested in suicide attempts or as an ethanol substitute.

Course: early CNS depression, followed by delayed toxicity (4-12 hours) that is often MORE severe — metabolic acidosis, RENAL FAILURE (the specific target organ, distinguishing it from methanol's ocular target), seizures, coma, death.

Mechanism: ethylene glycol -> glycolaldehyde -> glycolic acid and oxalic acid (via alcohol dehydrogenase) — oxalate specifically precipitates as calcium oxalate crystals in the renal tubules, driving the characteristic renal failure.

Exam/urine finding: envelope- and needle-shaped (calcium) oxalate crystals may be visible in the urine — a specific, supportive diagnostic clue when present, though its absence does not exclude the diagnosis.

Additional symptoms: flank pain, cardiopulmonary abnormalities alongside the neurologic and renal findings.

4. Isopropanol

Sources: rubbing alcohol and other household compounds, ingested as an ethanol alternative.

Presentation: GI irritation, upper GI bleeding, CNS depression, respiratory depression; fruity breath odor (from acetone production), ketosis, elevated osmolar gap.

KEY DISTINGUISHING FEATURE: isopropanol toxicity LACKS an anion gap metabolic acidosis — unlike methanol and ethylene glycol, isopropanol is metabolized to acetone (via alcohol dehydrogenase), NOT to an organic acid — elevated osmolar gap WITHOUT anion gap acidosis points specifically toward isopropanol rather than the other two toxic alcohols.

Management is LARGELY SUPPORTIVE (unlike methanol/ethylene glycol, which require specific antidotal therapy) — no fomepizole indication, since there is no toxic acid metabolite to block. Screen for hypoglycemia in confused/comatose patients and treat with thiamine 500mg then 25g dextrose IV. Hemodialysis may remove isopropanol but is RARELY necessary given the generally supportive-care-responsive course. Manage upper GI bleeding with standard therapies (see Upper GI Bleed protocol, GI & Hepatology System).

5. Immediate Stabilization (ABCDE)

Airway/Breathing: support per standard indications; respiratory failure can occur in severe methanol/ethylene glycol toxicity.

Circulation/Metabolic — antidotal therapy is the central intervention for methanol and ethylene glycol:

Fomepizole (competitive alcohol dehydrogenase inhibitor — blocks toxic metabolite formation for BOTH methanol and ethylene glycol):

• Dosing: 15mg/kg IV over 30 minutes, then 10mg/kg IV every 12 hours for 4 doses, then 15mg/kg IV every 12 hours as needed until the serum methanol/ethylene glycol level is <20 mg/dL
• Indications for methanol: level >20 mg/dL, acidemia, or elevated osmolal gap
• Indications for ethylene glycol: level >20 mg/dL, presence of acidosis, or elevated osmolal gap
• Ethanol is a LESS EFFECTIVE and MORE TOXIC alternative inhibitor if fomepizole is unavailable — not preferred, but a fallback option
• DO NOT combine ethanol and fomepizole simultaneously — fomepizole INCREASES the half-life of ethanol, creating an unpredictable and potentially dangerous interaction; use one or the other, not both

Adjunctive cofactor therapy:

• Methanol: folic acid 50mg IV every 6 hours to promote conversion of formate to CO2 and water (accelerating clearance of the toxic metabolite)
• Ethylene glycol: thiamine 100mg IV and pyridoxine 100mg IV to promote metabolism of ethylene glycol toward less toxic pathways

Checklist:

6. Hemodialysis Indications

Methanol: coma, seizures, new visual deficit, pH <=7.15, serum anion gap >24 mmol/L, impaired renal function, level >70 mg/dL, or persistent acidosis despite standard therapy.

Ethylene glycol: serum anion gap >23 mmol/L, impaired renal function, level >50 mmol/L, osmolal gap >50, coma, seizures, or worsening clinical status.

Isopropanol: hypotension, clinical worsening, or level >400 mg/dL — rarely necessary given the generally benign, supportive-care-responsive course.

General principle: hemodialysis removes BOTH the parent alcohol and (for methanol/ethylene glycol) the toxic metabolites, making it doubly effective; prompt nephrology and medical toxicology consultation should be obtained whenever hemodialysis is being considered, and treatment (fomepizole + dialysis planning) should be initiated rapidly without waiting for definitive level confirmation in a clinically compelling presentation.

Fomepizole should be CONTINUED alongside hemodialysis (dosing may need adjustment given dialysis clearance of the drug itself — consult toxicology/pharmacy) and continued until the target level (<20 mg/dL) is achieved.

7. Investigations

Anion gap, osmolar gap (both, per Section 1), serum methanol/ethylene glycol/isopropanol level if available (understanding the late-presentation limitation for methanol specifically), ABG, electrolytes, renal function (ethylene glycol-specific concern), urinalysis with microscopy (oxalate crystals — ethylene glycol), lactate (can be falsely elevated by glycolic acid cross-reactivity with some lactate assays in ethylene glycol poisoning — be aware of this potential artifact), formate level if available and methanol suspected with a late/undetectable methanol level, funduscopic exam (methanol).

8. Organ Support

Fomepizole (or ethanol as a less-preferred alternative, never combined) for methanol/ethylene glycol; hemodialysis per Section 6 indications; cofactor therapy (folic acid, thiamine, pyridoxine) per the specific alcohol; standard ICU supportive care; RRT for ethylene glycol-associated renal failure per standard AKI/CRRT protocol principles if it develops.

9. Consultation Matrix

10. Monitoring Framework

Serial anion gap and osmolar gap trend, serum methanol/ethylene glycol level trend (until <20 mg/dL), renal function (ethylene glycol), visual/funduscopic exam trend (methanol), ABG/pH trend, urine output.

11. Complications

Permanent visual loss/blindness (methanol, formate-mediated optic nerve toxicity), renal failure (ethylene glycol, oxalate-mediated), severe metabolic acidosis, seizures, coma, death if treatment delayed. Prevention: early empiric fomepizole initiation without waiting for level confirmation, appropriate hemodialysis threshold application, avoiding the ethanol+fomepizole combination, correct cofactor administration. Rescue: hemodialysis for severe/refractory cases, standard seizure/coma supportive management.

12. Escalation & De-escalation

Escalate: hemodialysis indication criteria met (Section 6) -> initiate dialysis alongside continued fomepizole.

De-escalate: methanol/ethylene glycol level <20 mg/dL, acidosis resolved, no ongoing organ dysfunction -> discontinue fomepizole, wean monitoring, transition to standard care.

13. ICU Discharge Criteria

Serum alcohol level <20 mg/dL (methanol/ethylene glycol) or clinical resolution (isopropanol), acid-base status normalized, no ongoing renal failure (or established RRT plan if renal recovery incomplete), visual assessment stable/documented (methanol), psychiatric evaluation completed if intentional ingestion.

14. Documentation & Medicolegal Checklist

15. Key Guidelines

Barceloux DG, Bond GR, Krenzelok EP, et al. American Academy of Clinical Toxicology practice guidelines on the treatment of methanol poisoning. J Toxicol Clin Toxicol. 2002;40(4):415-446. Barceloux DG, Krenzelok EP, Olson K, Watson W. American Academy of Clinical Toxicology practice guidelines on the treatment of ethylene glycol poisoning. J Toxicol Clin Toxicol. 1999;37(5):537-560.

16. Controversies

The precise osmolar gap threshold for excluding toxic alcohol poisoning is unreliable given individual variability in baseline osmolar gap and the time-dependent narrowing effect — clinical judgment must supersede a single cutoff value. Optimal fomepizole dosing during concurrent hemodialysis requires individualized adjustment given limited standardized dosing guidance, typically requiring toxicology/pharmacy input.

17. References

1. Toxicology (Alcohols section). Washington Manual of Critical Care, 4th ed, 2025 (Ch. 36).
2. Barceloux DG, Bond GR, Krenzelok EP, et al. AACT practice guidelines on the treatment of methanol poisoning. J Toxicol Clin Toxicol. 2002;40(4):415-446.
3. Barceloux DG, Krenzelok EP, Olson K, Watson W. AACT practice guidelines on the treatment of ethylene glycol poisoning. J Toxicol Clin Toxicol. 1999;37(5):537-560.

See also: Organophosphate Poisoning (Toxicology System) for the shared general poisoned-patient framework and hemodialysis/hemoperfusion indication table; Severe Metabolic Acidosis (Renal System) for the full anion gap/osmolar gap calculation methodology.