Practice Test Geeks(PSA) Prescribing Safety Assessment Practice Test
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Drug Interactions Flashcards

7 cards from real PSA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Drug Interactions flashcards as text

  1. A patient stabilized on warfarin begins rifampicin for tuberculosis. What is the most likely effect on the INR?

    Answer: INR decreases due to CYP2C9 induction by rifampicin

    Rifampicin is a potent CYP2C9 inducer that accelerates warfarin metabolism, substantially reducing its anticoagulant effect and lowering the INR.

  2. A patient on simvastatin 40 mg is prescribed clarithromycin for a respiratory infection. What is the primary risk?

    Answer: Increased risk of myopathy or rhabdomyolysis due to elevated simvastatin levels

    Clarithromycin potently inhibits CYP3A4, the primary enzyme metabolizing simvastatin, causing plasma accumulation and a significantly increased risk of muscle toxicity.

  3. A patient receiving standard-dose codeine reports no pain relief. Which CYP enzyme variant most likely explains this pharmacogenomic interaction?

    Answer: CYP2D6 poor metabolizer preventing conversion of codeine to morphine

    CYP2D6 converts codeine to its active analgesic metabolite morphine; poor metabolizers (7–10% of Caucasians) derive minimal analgesia from codeine.

  4. Fluoxetine (a potent CYP2D6 inhibitor) is started in a patient already taking tramadol. What is the most important risk?

    Answer: Tramadol accumulation and serotonin syndrome risk due to CYP2D6 inhibition

    Fluoxetine inhibits CYP2D6, which metabolizes tramadol to its active form; inhibition elevates parent tramadol levels and impairs serotonin reuptake clearance, raising serotonin syndrome risk.

  5. A patient on combined oral contraceptives starts carbamazepine for epilepsy. What is the pharmacokinetic mechanism of concern?

    Answer: CYP3A4 induction by carbamazepine reduces estrogen and progestogen plasma levels

    Carbamazepine is a potent CYP3A4 inducer that accelerates hepatic metabolism of ethinylestradiol and progestogens, reducing contraceptive hormone levels and risking contraceptive failure.

  6. Omeprazole co-prescription reduces the antiplatelet efficacy of clopidogrel. What is the mechanism?

    Answer: CYP2C19 inhibition by omeprazole reduces conversion of clopidogrel to its active thiol metabolite

    Clopidogrel is a prodrug requiring CYP2C19 for bioactivation; omeprazole inhibits this enzyme, reducing formation of the active metabolite and diminishing platelet P2Y12 inhibition.

  7. A patient on long-term methadone maintenance is started on phenytoin for new-onset seizures. What is the anticipated outcome?

    Answer: Opioid withdrawal symptoms from phenytoin-induced increase in methadone clearance

    Phenytoin is a broad enzyme inducer (CYP3A4, CYP2C9) that significantly accelerates methadone metabolism, precipitating opioid withdrawal in dependent patients.