This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Pharmacology
Mechanism of action of ethanol in methyl alcohol poisoning: 
Select and explain. 
A. Competitively inhibits alcohol Dehydrogenase, B. Selectively inhibits catalase, C. Competitively inhibits lactate dehydrogenase, D. Competitive inhibition of acetaldehyde dehydrogenase
A: Competitively inhibits alcohol Dehydrogenase
Answer: A: Competitively inhibits alcohol Dehydrogenase 
Explanation: (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.