How can pharmacokinetic drug-drug interactions arise?

• A. If one drug changes the receptor binding of another.
• B. If one drug changes the pharmacodynamics of another.
• C. If one drug changes the absorption, distribution, metabolism, or excretion of another drug, thereby altering the concentration of active drug in the body.
• D. If one drug influences taste.

Answer: (C)

Pharmacokinetic drug-drug interactions occur when one drug changes how another is handled by the body, altering the amount of active drug that reaches systemic circulation and tissues. This centers on the four ADME processes: absorption, distribution, metabolism, and excretion. If a second drug enhances or inhibits absorption, changes where the drug distributes in the body (for example by displacing it from plasma proteins or altering tissue penetration), speeds up or slows down metabolism (enzyme induction or inhibition), or affects renal or biliary excretion, the resulting plasma concentration—and thus the drug’s effect and toxicity risk—will change. These changes in concentration explain pharmacokinetic interactions. By contrast, altering receptor binding or the drug’s pharmacodynamic effect can occur without changing drug levels, and taste changes are not relevant to pharmacokinetics.