Mechanism of action of ethanol in methyl alcohol poisoning:
Competitively inhibits alcohol Dehydrogenase
Selectively inhibits catalase
Competitively inhibits lactate dehydrogenase
Competitive inhibition of acetaldehyde dehydrogenase
(Ref: Katzung, 14th ed. pg. 404; KDT, 6th ed. pg. 387)* Ethanol acts by competitive inhibition of alcohol dehydrogenase which block further metabolism of methanol into formaldehyde and formic acid. These products also cause retinal damage leading to subsequent blindness.ADH: alcohol dehydrogenase: FDH : formaldehyde dehydrogenase F-THF-S: 10-formyl tetrahydrofolate synthetase* Catalase is a common enzyme found in nearly all living organisms exposed to oxygen. It catalyzes the decomposition of hydrogen peroxide to water and oxygen* Lactate dehydrogenase: Dummy choice and is present in heart, RBC and is used as marker for malignancy.* Acetaldehyde dehydrogenase: Converts acetaldehyde into acetic acid and is the target for disulfiram which is used to help patients quit alcohol.Remember* Ethanol is also metabolized by alcohol dehydrogenase and acts as its competitive inhibition. The enzyme's affinity for ethanol is 10-20 times higher than it is for methanol. Given via IV infusion in methanol or ethylene glycol poisoning.* Fomepizole inhibits alcohol dehydrogenase. It is a stronger competitive inhibitor of ADH and, in addition, does not cause hypoglycemia or sedation.* Fomepizole is relatively easier to administer than ethanol. It does not require monitoring of serum concentrations. Hence considered as drug of choice.
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