NAPLEX (North American Pharmacist Licensure Examination) Practice Exam

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Azathioprine should be avoided with which type of medication due to increased risk of myelosuppression?

  1. CYP3A4 inhibitors

  2. Xanthine oxidase inhibitors

  3. P-glycoprotein substrates

  4. MTOR inhibitors

The correct answer is: Xanthine oxidase inhibitors

Azathioprine should be avoided with xanthine oxidase inhibitors due to increased risk of myelosuppression. Azathioprine is metabolized by xanthine oxidase, so combining the two medications could result in higher levels of azathioprine in the body. This may lead to toxicity, which can include decreased white blood cell count and an increased risk of myelosuppression. CYP3A4 inhibitors may also interact with azathioprine, but not to the same extent as xanthine oxidase inhibitors. P-glycoprotein substrates and MTOR inhibitors do not have significant interactions with azathioprine.