NAPLEX (North American Pharmacist Licensure Examination) Practice Exam

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What is common between carbamazepine, phenytoin, and rifampin?

  1. They are all CYP-1A2 inhibitors

  2. They are all CYP-3A4 substrates

  3. They are all CYP-3A4 inducers

  4. They are all CYP-2C9 substrates

The correct answer is: They are all CYP-3A4 inducers

Carbamazepine, phenytoin, and rifampin are all known as CYP-3A4 inducers. These medications have the ability to increase the activity of the CYP-3A4 enzyme, leading to an acceleration in the metabolism of drugs that are substrates for this enzyme. This can result in decreased plasma concentrations and reduced efficacy of other medications that are metabolized by CYP-3A4. This is an important pharmacokinetic interaction to be aware of when managing patients on multiple medications.

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