NAPLEX (North American Pharmacist Licensure Examination) Practice Exam

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Which is a substrate of CYP-2C9?

  1. S-warfarin

  2. R-warfarin

  3. Fentanyl

  4. Diltiazem

The correct answer is: S-warfarin

S-warfarin is the correct answer because it is a well-known substrate of the CYP-2C9 enzyme. CYP-2C9 is responsible for the metabolism of a variety of drugs, including S-warfarin. Warfarin is a racemic mixture of two enantiomers: S-warfarin (the more potent anticoagulant) and R-warfarin. CYP-2C9 primarily metabolizes S-warfarin to inactive metabolites, resulting in its anticoagulant effect. Therefore, S-warfarin being a substrate of CYP-2C9 makes it the correct answer. Among the other options, R-warfarin, Fentanyl, and Diltiazem are not substrates of CYP-2C9.

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