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