Pharmacodynamics is best defined as which of the following?

• A. Movement of a drug through the body
• B. Excretion of a drug from the body
• C. Interaction between a medication and the body
• D. Metabolic modification of a drug

Answer: (C)

Pharmacodynamics describes how a drug produces its effects in the body. It focuses on the interaction between the medication and the body's receptors and signaling processes, including the mechanism of action, dose–response relationships, and factors that influence the magnitude of the effect. This helps explain how strong the effect will be at a given dose, when it appears, and how long it lasts. Movement of a drug through the body (absorption, distribution), excretion, and metabolic modification describe what the body does to the drug—pharmacokinetics—so they’re about the body's handling of the drug, not the drug’s effects on the body.