Which reagent is used to treat ethylene glycol poisoning by blocking alcohol dehydrogenase?

• A. N-acetylcysteine
• B. Ethanol or fomepizole
• C. Activated charcoal
• D. Methanol

Answer: (B)

Ethylene glycol poisoning causes harm because alcohol dehydrogenase metabolizes it into glycolic and oxalic acids, which drive metabolic acidosis and organ injury. The way to treat this is to stop that metabolic step by blocking the enzyme. Ethanol and fomepizole do exactly that: they prevent alcohol dehydrogenase from converting ethylene glycol into toxic metabolites. Fomepizole is the preferred option because it is a specific inhibitor with minimal side effects, while ethanol can be used as an alternative but comes with intoxication and monitoring considerations. By inhibiting the enzyme, ethylene glycol remains unmetabolized and is eliminated, reducing progression of acidosis and kidney damage; dialysis may be needed in severe cases.

N-acetylcysteine treats acetaminophen toxicity, not ethylene glycol. Activated charcoal has limited role once significant absorption has occurred and does not block the enzyme. Methanol is a toxic alcohol, not a therapeutic agent for this condition, though it too is metabolized by the same enzyme.