Learning Objective
The objective of this lesson is to enable the learner to understand the fundamental principles of pharmacodynamics, including how drugs interact with receptors, the distinction between agonists and antagonists, and the key concepts of affinity, potency, and efficacy, as well as how these properties determine the magnitude and quality of drug responses.
Pharmacodynamics — Definitions
Pharmacodynamics explains what a drug does to the body, focusing on how drugs bind to receptors and produce effects.
Activity
Agonists
Agonists are drugs that bind to receptors and activate them, producing a biological response.
Antagonists
Antagonists are drugs that bind to receptors but do not activate them. Their effect comes from blocking agonists and preventing activation.
Affinity
Affinity refers to the ability of a drug to bind to its receptor. Higher affinity means the drug binds more strongly and requires a lower concentration to occupy receptors.
Potency
Potency refers to the amount of drug needed to produce a specified effect. A more potent drug requires a smaller dose to achieve the same response.
Efficacy
Efficacy is the maximum effect a drug can produce, regardless of dose. It reflects the drug’s ability to generate a biological response once bound to receptors.
