Describe pharmacodynamics versus pharmacokinetics.

• A. Pharmacodynamics studies how the body processes the drug; pharmacokinetics studies how the drug acts on the body
• B. Pharmacodynamics is about dosage; pharmacokinetics about interactions
• C. Pharmacodynamics describes how the drug interacts with the body; pharmacokinetics describes absorption, distribution, metabolism, and excretion
• D. They are the same

Answer: (C)

Pharmacodynamics asks what the drug does to the body—how it binds to receptors or targets, the resulting effect, and how the response changes as the dose changes. Pharmacokinetics asks what the body does to the drug—how it is absorbed into the bloodstream, distributed to tissues, metabolized, and ultimately eliminated. This distinction explains the timing and magnitude of effects: pharmacokinetics determines concentrations at the site of action over time, while pharmacodynamics determines the actual effect those concentrations produce.

The best way to state this is that pharmacodynamics describes how the drug interacts with the body, and pharmacokinetics describes absorption, distribution, metabolism, and excretion. The other options swap concepts, focus on less comprehensive ideas, or say they’re the same, which doesn’t fit how these two areas differ.