In: Nursing
There was a 2-year old admitted to the hospital for methanol poisoning. Why is methanol poisoning a life threatening scenario? What did the doctors do to the 2-year old to treat the poisoning? Please explain how and why this treatment works.
Methanol is rapidly absorbed from stomach, lungs and intestine.
It reaches a maximum concentration 30-90 min after its intake.
During it's metabolism it gets converted into formaldehyde and formic acid(see the image above). Without competition for the enzyme alcohol dehydrogenase, methanol undergo zero order metabolism but if ethanol or fomepizole is present it undergo 1st order metabolism.
ACTION
1.Ethanol like action:
Methanol act as a depressant of certain specialized and sensitive cells of cerebral cortex (centres regulating conduct, judgment and self-criticism) with release of inhibitory neurotransmitters, leading to unrestrained behavior(loss of inhibition). This is followed by depression of vital centres of medulla producing coma and death.
2. Increased serum osmolality
3. Formic acid causes metabolic acidosis and retinal toxicity.
This is why methanol poisoning is a life threatening scenario.
TREATMENT
1. GASTRIC LAVAGE - To prevent absorption:
5% sodium bicarbonate solution is used and 500 cc is left in the stomach.
2. BICARBONATE - To prevent acidosis:
Oral administration of sodium bicarbonate, 2 g in 250 ml of water, 4 hourly.
3. Folate therapy - Reduce blood formate levels by increasing it's metabolism :
Calcium folinate/leucovorin (calcium salt of folinic acid) IV. High dose of folinic acid (50-75 mg every 6 hourly) is indicated. Thiamine and pyridoxine may be given.
4. ETHANOL - Competitive antagonist:
Loading dose of 0.8-1 ml/kg orally of 95% ethanol (v/v) in 200 ml of orange juice or 7.6-10 ml/kg IV of 10% ethanol (v/v) in D5W over 30 min, and then maintenance dose of 0.15 ml/kg/h orally or 1.4 ml/kg/h IV. Desired serum ethanol concentration is 100-150 mg/dl.
5. FOMEPIZOLE - Antidote:
4-methylpyrazole (fomepizole) is a competitive inhibitor of alcohol dehydrogenase. It blocks the formation of formaldehyde and formic acid and can be used instead of ethanol. Loading dose of 15 mg/kg over 30 min, followed by 10 mg/kg every 12 h for 4 doses, then 15 mg/kg every 12 h.
6. Other measures:
• Eyes should be kept covered to protect them from light.
• Hemodialysis as soon as possible in case of severe poisoning.
• Symptomatic treatment.