American Association of Critical-Care Nurses (AACN) Certification Practice Test

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Which enzyme does fomepizole inhibit to help treat overdose?

Alcohol dehydrogenase
CYP450
Aldose reductase
Acetaldehyde dehydrogenase

The correct answer is: Alcohol dehydrogenase

Fomepizole is primarily used as an antidote in cases of methanol and ethylene glycol poisoning. It works by inhibiting alcohol dehydrogenase, which is the enzyme responsible for metabolizing these toxic substances into more harmful metabolic products. By blocking this enzyme, fomepizole effectively prevents the conversion of methanol into formaldehyde and formic acid, and of ethylene glycol into toxic metabolites, thereby reducing toxicity and allowing time for the body to eliminate the harmful substances without producing additional harmful metabolites. While the other enzymes listed play roles in various metabolic pathways, they are not directly inhibited by fomepizole in the context of treating overdose. For instance, CYP450 is involved in broader drug metabolism, and inhibiting it would not specifically target the metabolism of methanol or ethylene glycol. Aldose reductase is more associated with carbohydrate metabolism, and acetaldehyde dehydrogenase is involved in the breakdown of acetaldehyde, a product of ethanol metabolism. Thus, the specific impact of fomepizole on alcohol dehydrogenase is crucial for its role in preventing the toxic effects of methanol and ethylene glycol.