Toxin

Methanol Poisoning

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Methanol Poisoning, Methanol, Carbinol, Methyl Alcohol, Wood Alcohol, Wood Naptha

  • See Also
  1. Unknown Ingestion
  2. Anion Gap Metabolic Acidosis
  • Epidemiology
  1. U.S.: 1000 to 5000 Poisoning per year
  • Pathophysiology
  1. Methanol is a common industrial and household solvent (paint remover) and fuel additive
    1. Antifreeze
    2. Perfume
    3. Pain solvents
    4. Paints, Varnishes and Shellacs
    5. Windshield washing fluid
    6. Carburetor cleaner
    7. Fracking Fluid
    8. Adhesives
  2. Mechanisms of ingestion
    1. Accidental Ingestion by children
    2. Industrial workers may inhale Methanol vapors (e.g. formaldehyde production, shellac processing)
    3. Alcoholism with Methanol ingestion when Alcohol unavailable
    4. Bootleg Alcohol (especially in developing nations, and where outlawed in conservative countries)
      1. In 2018, >150 deaths were reported due to Methanol-laced counterfeit liquor
      2. In the 1920s during U.S. prohibition, industrial Alcohols were mandated to be laced with Methanol
  3. Methanol is quickly absorbed by the Gastrointestinal Tract
    1. Serum levels peak within 60-90 minutes of ingestion
  4. Hepatic Metabolism
    1. Methanol is metabolized into Formaldehyde (via Alcohol dehydrogenase)
    2. Formaldehyde is metabolized into Formic Acid (via aldehyde dehydrogenase)
    3. Formic acid is the primary toxin resulting in most of the ingestion-related damage and Metabolic Acidosis
    4. Formic acid is very slowly metabolized into carbon dioxide and water (via Tetrahydrofolate)
  • Findings
  1. Symptom onset is delayed 12-24 hours from ingestion
    1. Related to delay in metabolism to formic acid
  2. Neurologic
    1. Headache
    2. Altered Level of Consciousness and Intoxication
    3. Seizure
    4. Extrapyramidal symptoms
    5. Parkinsonism
    6. Paresthesias
    7. Tinnitus (from Ototoxicity)
  3. Cardiopulmonary
    1. Dyspnea
    2. Tachypnea
    3. Kussmaul Respirations (due to Metabolic Acidosis)
    4. Hypotension (or Hypertension)
    5. Bradycardia
  4. Gastrointestinal
    1. Nausea or Vomiting
    2. Abdominal Pain
    3. Pancreatitis
  5. Ocular
    1. Blurred Vision
    2. Double Vision
    3. Progressive Vision Loss to blindness
    4. Funduscopic Exam
      1. Early: Retinal hyperemia
      2. Late: Pale, avascular Retina
  • Lab
  1. Serum Methanol level
    1. Available at many community hospitals
    2. Toxic levels >10 mg/dl
  2. Serum Lipase or Serum Amylase
  3. Metabolic panel
    1. Decreased serum bicarbonate
    2. Anion Gap Metabolic Acidosis (due to formic acid, Lactic Acid)
    3. Osmolal Gap
      1. Serum Osmolality increases 30.9 mmol/L for every 100 mg/dl serum Methanol
    4. Hypomagnesemia
    5. Hypophosphatemia
    6. Increased Serum Creatinine (Acute Kidney Injury)
  • Differential Diagnosis
  1. See Altered Level of Consciousness
  2. See Toxic Ingestion
  3. See Vision Loss
  4. Ethylene Glycol Toxicity
  5. Liver failure (hyperammonemia)
  6. Renal Failure (Uremia)
  7. Head Injury
  8. Encephalitis
  9. Meningitis
  • Complications
  1. Vision Loss
    1. Formic acid causes Optic Nerve demyelination
    2. Occurs with serum Methanol levels >20 mg/dl
    3. Onset of ocular changes within 48 hours of ingestion
  2. Parkinsonism
    1. Methanol and metabolites cause Basal Ganglia damage resulting in Parkinsonian-like signs
    2. Onset weeks after ingestion
  3. Hemorrhagic Pancreatitis
    1. Occurs in more than two thirds of Methanol Poisoning
  4. Death
    1. Minimum toxic dose: 0.1 ml/kg
    2. Minimum lethal ingestion: 1 mg/kg
    3. Even one tbs of 40% Methanol can kill an adult
  • Management
  1. Avoid Gastric Decontamination (not helpful, rapid absorption)
  2. Administer folinic acid (or Folic Acid): 1 mg/kg up to 50 mg
  3. Fomepizole (Antizol)
    1. Start immediately if Methanol toxicity is suspected
    2. Continue Fomepizole if
      1. Methanol level >20 mg/dl
      2. Osmolal Gap >10 mOsm/L
      3. Serum bicarbonate <20 mmol/L
  4. Hemodialysis Indications
    1. Severe acidosis with pH <7.25
    2. Methanol Level >50 mg/dl
    3. Visual Symptoms
  5. Disposition
    1. Admit all patients requiring Fomepizole or Hemodialysis
    2. Discharge Indications at 4-6 hours
      1. Normal bicarbonate and Osmolal Gap
  • References
  1. Korabathina in Ramachandran (2012) Methanol Toxicity, EMedicine
  2. Leikin (1996) Poisoning and Toxicology, Lexi-Comp, Cleveland, p. 957-8
  3. Rodriguez (2022) Crit Dec Emerg Med 36(4): 26-31
  4. Swadron and Nordt in Herbert (2013) EM:Rap 13(8): 3
  5. Tomaszewski (2019) Crit Dec Emerg Med 33(7): 28