Adverse Drug Reactions and Interactions · USMLE Step 1

Which scenario best illustrates a pharmacodynamic drug–drug interaction?

CYP enzyme inhibition by one drug reducing the clearance of another
Competition for renal excretion causing increased levels
Two drugs that both depress respiratory center effects when combined
One drug binding to plasma protein displacing another

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Correct answer: Two drugs that both depress respiratory center effects when combined

Pharmacodynamic interactions occur when drugs influence the same physiological pathway; additive depressant effects (e.g., CNS or respiratory) increase toxicity risk.

Difficulty: Medium Question 8 of 19

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