Methanol and ethylene glycol poisoning

Learning objectives

Diagnose and treat intoxication with the toxic alcohols methanol and ethylene glycol (EG)

EG is a common component of antifreeze and de-icing solutions
Methanol is present as a solvent in many household products, such as antifreeze, cleaning solutions, dyes, and paint removers
Onset of symptoms of methanol poisoning can range from 40 minutes to 72 hours, depending on the dose and co-ingestion of ethanol

Toxicity of methanol and EG is related to the production of toxic metabolites by the hepatic enzyme alcohol dehydrogenase (ADH)

Oxalic acid
- The main toxic metabolite of EG
- Binds to calcium, forming insoluble calcium oxalate crystals, this can cause hypocalcemia and crystal deposition in several organs causing organ dysfunction
Formic acid
- The main toxic metabolite of methanol
- Directly toxic to the retina which can cause visual disturbances and even blindness
- Inhibits the mitochondrial cytochrome oxidase, which deranges ATP synthesis

	Ethylene glycol	Methanol
Early	Confusion Stupor Nausea Vomiting	Mild euphoria Drunkenness Headache Lethargy Confusion
Progression	Metabolic acidosis Küssmaul breathing Hypocalcemia Hyperreflexia	Vision abnormalities Extrapyramidal symptoms (in severe intoxication) Seizures Metabolic acidosis Küssmaul breathing
Late	Coma Acute renal failure (earlier in severe intoxication) Cardiovascular shock Multi organ failure Death	Blindness Coma Cardiovascular shock Respiratory failure Sudden respiratory arrest Death

Decreased consciousness
- Requires endotracheal intubation if airway is at risk
- Administer a pre-intubation bolus of 1-2 mmol/kg sodium bicarbonate to avoid exacerbating acidosis, which will worsen symptoms
Supportive care
- IV fluids
- Vasopressors as needed
- Correct acidemia (pH<7.3) by administering sodium bicarbonate
- Supplement calcium in EG intoxication
Decontamination
- Activated charcoal and gastric lavage have no place in the treatment of toxic alcohol intoxication
Seizures
- Treat with a benzodiazepine
Antidotal therapy:

Hemodialysis
- Start hemodialysis if
  - Methanol/EG intoxication with: Coma, convulsions, renal failure, metabolic acidosis pH<7.15, persisting acidosis despite treatment or serum anion gap>24 mmol/L
  - Plasma concentration ≥500 mg/L if not yet antidotal treatment, ≥600 mg/L if ethanol, ≥700 mg/L if fomepizole