Which statement correctly differentiates pharmacodynamics from pharmacokinetics?

Which statement correctly differentiates pharmacodynamics from pharmacokinetics?

• A. What the body does to the drug; What the drug does to the body
• B. What the drug does to the body; What the body does to the drug
• C. The pharmacodynamics concerns the amount of drug in the blood; The pharmacokinetics concerns the effect on tissues
• D. The pharmacodynamics concerns the rate of absorption; The pharmacokinetics concerns the onset of action

Answer: (B)

The main idea is the directional relationship: pharmacodynamics explains what the drug does to the body, including how it produces its therapeutic and adverse effects through mechanisms like receptor binding and dose–response relationships. Pharmacokinetics explains what the body does to the drug, covering absorption, distribution, metabolism, and excretion, which determine the drug’s concentration over time and how quickly effects appear or wear off. So, the statement that pairs “what the drug does to the body” with “what the body does to the drug” correctly differentiates the two. For example, pharmacodynamics would describe how a drug activates a receptor to reduce pain, while pharmacokinetics would describe how quickly that drug is absorbed after oral dosing, how it’s distributed to tissues, and how it’s cleared from the body.