Answers and Discussion

Answers and Discussions to the Questions:

• What products contain methanol and how is it toxic to the body?
  
  Methanol is found in paint remover, solvents, paint, varnish and automotive products.   However, these products may also contain ethanol, which will slow the onset of signs of methanol intoxication.  In the body, about 30% of the methanol is excreted by the lungs as carbon dioxide while 5% is excreted by the kidneys as formic acid.   The rest is broken down by alcohol dehydrogenase into toxic metabolites.  A metabolic acidosis develops 2-12 hours later and the animal may also show signs of pancreatitis.
  
• What clinical signs are seen with methanol toxicity?
  
  Signs of methanol toxicity include nausea, vomiting, gastric pain, dyspnea, ataxia, hypothermia and hyperexcitability.  In severe cases, you can see convulsions, opisthotonus, fixed pupils and coma.
  
• What initial emergency treatments would you institute for "Kato", one of which can be done by owners at home at the first sign of ingestion of methanol?
  
  Gastric lavage should be done to rid the stomach of any undigested methanol.   For recent ingestions in alert animals, induce vomiting with apomorphine.  Or the owner can induce vomiting at home if they are sure the animal ingested methanol.   This can be done by giving the animal a tablespoon of hydrogen peroxide or a teaspoon of salt or mustard.  After lavaging the stomach, give activated charcoal if the patient is alert.  Provide oxygen via a mask if the animal is dyspneic.   Then start diuresis at 1.5 times maintenance.
  
• Which two therapeutic agents are used to treat methanol toxicity for the next 24-48 hours?
  
  These agents are either 4-methylpyrrazole (4MP) or 20% ethanol.  4MP is a noncompetitive inhibitor of alcohol dehydrogenase, decreasing the metabolism of methanol.   4MP is for use in dogs only.  The dose schedule is as follows:  Dose 1 (0 hours) = 20 mg/kg IV; Dose 2 (12 hours) = 15 mg/kg IV; Dose 3 (24 hours) = 15 mg/kg IV; Dose 4 (36 hours) = 36 mg/kg IV.  Ethanol competes with alcohol dehydrogenase to prevent the formation of the toxic metabolites.  20% ethanol can be made by diluting 80 proof vodka with an equal amount of saline, or by diluting 180 proof everclear with saline at a ratio of 1:3.5.  The ethanol is given IV for 2-3 days but is not very successful in treating patients who are presented 4 hours or longer post-ingestion.   It can be given as a CRI of 1 ml/kg/hr, or it can be given as a bolus over 15 minutes.  For dogs, the dose is 5.5 ml/kg IV every 5-6 hours.  For cats, the dose is 5 ml/kg IV every 5-6 hours.
  
• What parameters do you want to monitor closely for the next few days to make sure treatment is going well?
  
  The biggest problem to overcome is the metabolic acidosis.  If possible, monitor blood gases (pH and bicarb)--you may need to give sodium bicarbonate IV.   Also monitor urine output or BUN/creatinine for renal function.  Watch for signs of overhydration like chemosis, increased lung sounds or increased central venous pressure.
  
• What is the prognosis for methanol toxicity?
  
  Prognosis depends on the severity of toxicity.  It is considered fair to good for animals that are still pretty alert.  It is considered poor for cases with coma or convulsions.

• Follow-Up: "Kato" spent one night in the critical care unit with intravenous diuresis.  His owners declined 4MP or ethanol.  By morning he was alert and no longer ataxic.  He was then sent home.

Methanol Toxicity Pearls

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Copyright 2000, Wayne E. Wingfield, Colorado State University   
This page was last edited:  03/01/00