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 lithium takes ibuprofen for 5 days. Lithium levels rise into the toxic range. What is the mechanism?

    Answer: Ibuprofen reduces renal prostaglandin synthesis, impairing lithium clearance and raising serum levels

    NSAIDs suppress prostaglandin-mediated afferent arteriolar dilation in the kidney, reducing GFR and the renal clearance of lithium, which has no hepatic metabolism.

  2. A patient on an irreversible MAOI consumes aged cheese and cured meats. What dangerous reaction is precipitated?

    Answer: Hypertensive crisis from tyramine-induced massive catecholamine release

    MAO-A in the intestinal wall normally metabolizes dietary tyramine; when inhibited, tyramine enters systemic circulation and triggers massive norepinephrine release from sympathetic nerve terminals, causing hypertensive crisis.

  3. Sildenafil is absolutely contraindicated with organic nitrates because this combination causes:

    Answer: Synergistic elevation of cGMP via combined NO and PDE5 pathways causing severe hypotension

    Nitrates release nitric oxide (stimulating guanylyl cyclase) and sildenafil blocks cGMP degradation (inhibiting PDE5); together they cause profound cGMP-mediated smooth muscle relaxation and potentially fatal hypotension.

  4. IV iodinated contrast is administered to a patient on metformin. The primary pharmacological risk is:

    Answer: Contrast-induced nephropathy impairing metformin renal elimination, risking lactic acidosis

    Iodinated contrast can cause acute tubular injury; if metformin clearance falls due to reduced GFR, it accumulates and inhibits hepatic mitochondrial respiration, promoting lactic acidosis.

  5. A patient on warfarin is prescribed metronidazole for a dental infection. The INR rises from 2.5 to 7.0. What is the primary mechanism?

    Answer: Metronidazole inhibits CYP2C9, the main enzyme metabolizing the more potent S-warfarin enantiomer

    Metronidazole is a potent CYP2C9 inhibitor; since S-warfarin (the more pharmacologically active enantiomer) is primarily metabolized by CYP2C9, its levels rise substantially, dramatically increasing the INR.

  6. Why must tetracyclines be taken at least 2 hours apart from antacids or iron supplements?

    Answer: Divalent and trivalent metal cations (Ca2+, Mg2+, Al3+, Fe3+) chelate tetracyclines, forming insoluble complexes with drastically reduced absorption

    Chelation of tetracycline rings by divalent/trivalent cations in antacids and iron supplements forms insoluble complexes in the GI lumen, reducing oral bioavailability by up to 90%.

  7. Protamine sulfate is administered to reverse heparin anticoagulation. Which interaction mechanism is involved?

    Answer: Direct electrostatic binding between positively charged protamine and negatively charged heparin chains, forming an inactive complex

    Protamine is a strongly cationic protein that neutralizes the anionic (negatively charged) heparin molecule through ionic binding, forming a stable, pharmacologically inactive complex.