FPGEE for National Association of Boards of Pharmacy (NABP) Practice Exam

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A patient on a medication that inhibits CYP3A4 may experience what type of drug interaction?

  1. Increased efficacy

  2. Decreased toxicity

  3. Enhanced metabolism

  4. Increased plasma concentration

The correct answer is: Increased plasma concentration

When a patient is on a medication that inhibits CYP3A4, the drug interaction that most commonly occurs is an increase in plasma concentration of drugs that are substrates for this enzyme. CYP3A4 is a key enzyme in the cytochrome P450 system responsible for the metabolism of many drugs. Inhibition of this enzyme leads to decreased metabolic clearance of medications that require CYP3A4 for elimination. As a result, these drugs can accumulate in the bloodstream, leading to higher plasma concentrations than intended. This can significantly affect the pharmacokinetics of the substrate drugs, potentially leading to increased efficacy or, more importantly, increased toxicity, depending on the specific medication involved. Therefore, understanding the effects of CYP3A4 inhibition is crucial for managing potential drug interactions in patients who are prescribed medications metabolized by this enzyme.