Which term describes the effects of drugs on target tissues after reaching them?

• A. Pharmacotherapeutics
• B. Absorption
• C. Pharmacokinetics
• D. Pharmacodynamics

Answer: (D)

The effects of drugs on target tissues after they reach them are described by pharmacodynamics. This area focuses on what the drug does to the body at the site of action: how it binds to receptors or enzymes, the cellular responses that follow, and how the magnitude of the effect relates to drug concentration (the dose–response relationship). This explains how a drug produces its therapeutic or adverse effects once it has arrived at its target.

Pharmacokinetics, by contrast, covers what the body does to the drug—absorption, distribution, metabolism, and excretion—before the drug can exert effects at the target. Pharmacotherapeutics deals with how drugs are used in patient care, including choosing and dosing therapies. Absorption is a specific pharmacokinetic process describing how a drug enters the bloodstream from its site of administration.

For example, morphine produces analgesia by binding to mu-opioid receptors in the brain and spinal cord. The resulting effect depends on receptor occupancy and the drug’s intrinsic activity, a classic pharmacodynamic concept.