Toxicology 10: Toxic Alcohols: Methanol and Ethylene Glycol
The four commonly ingested alcohols are ethanol, isopropyl alcohol, methanol and ethylene glycol.
Isopropyl alcohol (isopropanol, rubbing alcohol) is similar to ethanol in its effects. Although more potent than ethanol, complications are mainly due to CNS depression. Metabolic abnormalities develop only at high dosages and blood levels.
Methanol and ethylene glycol, on the other hand, are very toxic in small quantities. Their pathophysiologies and treatments are similar, but they differ in their specific characteristics.
Pathophysiology
Both ethylene glycol and methanol exert their toxicity through toxic metabolites so serious signs and symptoms may be delayed hours after ingestion.
Both produce serious end-organ damage (CNS, renal, eye).
Both produce an anion gap acidosis (Anion Gap = Na+ - [Cl- + HCO3- ], normal < 12). See Vol III—END/M6 Acid-Base.
Both produce an osmolal gap: Osm Gap = Measured osmolality - calculated osmolality. Osm (calc) = 2Na+ + BUN/2.8 + Glucose/18. The normal Osm Gap is < 10. Higher than normal indicates the presence of some osmotically active substance. To estimate concentration of an alcohol in mg/dL use the following formula: (osmolal gap - 10) x 3.2 for methanol, (osmolal gap - 10) x 6.2 for ethylene glycol. Caution: Osmolal gap is not always sensitive and should not be used as a substitute for measured levels.
Both are treated by competitive inhibition of alcohol dehydrogenase metabolism, followed by hemodialysis.
Methanol
Sources: Windshield washer fluids, gas line antifreeze, paints, and
solvents
Toxic dose: approx 0.5 cc/kg of 40% methanol or equivalent. (This is a
conservative estimate reflecting the lowest of a wide range of reported
toxic doses.)
Toxic blood level: 20 mg/dL
Unique diagnostic features: visual impairment, swelling of optic disc
Ethylene Glycol
Sources: radiator antifreeze, solvents
Toxic dose: approx 0.5 to 1 cc/kg of 100% ethylene glycol (conservative
estimate)
Toxic blood level: 20 mg/dL
Unique diagnostic features: Most radiator antifreezes have fluoroscein added, so stomach contents and urine will fluoresce under Woods; light; hypocalcemia may be present. Calcium oxalate crystals may form in the urine.
Treatment
Start treatment on the basis of reasonable suspicion of ingestion of
toxic quantities, pending blood levels.
Gastric lavage is useful in only the first hour after ingestion; charcoal is not useful.
Inhibition of metabolism
Ethanol competes with the toxic alcohols for alcohol dehydrogenase, so it is the first line of treatment. Dosages: IV 10% ETOH in D5W 10cc/kg over 30 to 60 minutes as loading dose, then 1 to 2 cc/kg/h to maintain blood level of 100 to 150 mg/dL. Use the lower dose for children and non-drinkers, the higher for alcoholics. May also be given orally: 40% ETOH (80 proof liquor) 2.5 cc/kg, then 0.3 cc/kg/h (low dose) or 0.5 cc/kg/h (high dose). Lower concentrations may be used with quantities adjusted accordingly. Watch for changes in LOC and (PEDS) in children, measure blood glucose frequently (every hour).
4 MP (Antizol) is a commercial alcohol dehydrogenase inhibitor. Advantages: intermittent dosing, no CNS depression. Disadvantages: cost, availability. Dose: Loading dose 15 mg/kg IV over 30 minutes, then 10 mg/kg every 12 h x 4 doses, then 15 mg/kg every 12 h.
Treat acid-base abnormalities with ethylene glycol. Watch for and treat hypocalcemia; give pyridoxine 100 mg IM/IV and thiamine 100 mg IM/IV to facilitate non-toxic pathways.
With methanol give folic acid 50 mg IV every 4 h to facilitate non-toxic pathway.
Hemodialysis is the definitive method for elimination of the toxic alcohol.