Chapter 5: Pharmacodynamics Learning Objectives 1. Define pharmacodynamics and its relationship to the action of drugs on the body. ● Pharmacodynamics is the study of how drugs interact with the body to produce their effects. It looks at how drugs work at the molecular, cellular, and physiological levels to impact the body. Chapter 5 Readings In Chapter 5, the basic features of the dose-response relationship are discussed, including maximal efficacy and relative potency. Dose-response curves reveal three phases: phase 1 where low doses have no measurable response, phase 2 where an increase in dose corresponds to an increase in response, and phase 3 where further increase in dose does not elicit a greater response. Pharmacodynamics is defined as the study of the biochemical and physiologic effects of drugs on the body and how they are produced. Bullet points Potency of a Drug ● ● ● ● Potency refers to the dosage needed to produce effects A more potent drug requires a smaller dose to achieve the same effect as a less potent drug If a drug is lacking in potency, large doses may be needed for beneficial effects Potency does not imply maximal efficacy (effectiveness) Maximal Efficacy ● ● ● Potency and efficacy are independent qualities of a drug A drug with higher potency may not be more effective than a drug with lower potency Drugs can have equal effectiveness even if one is more potent than the other Drug-Receptor Interactions ● ● Drugs interact with receptors to mimic or block the actions of endogenous compounds Receptors are points of control for physiological processes ● Drug-receptor interactions can either increase or decrease physiological activity Interaction of drugs with receptors ● ● ● Drugs bind to many cellular components Receptors are the most important group of macromolecules through which drugs exert their effects Receptors can be enzymes, ribosomes, tubulin, etc. Physiological role of receptors ● ● Under physiological conditions, cardiac output can be increased by the binding of norepinephrine (NE) to receptors on the heart These same receptors can be acted upon by drugs, either mimicking or blocking the actions of endogenous NE Mechanisms of receptor activation ● ● Receptor function is regulated by molecules supplied by the body Agonist drugs or endogenous ligands activate receptors, mimicking the action of the endogenous regulatory molecule Ligand-gated ion channels ● ● ● Ligand-gated ion channels regulate the flow of ions into and out of cells Activation of these receptors occurs when an endogenous ligand or agonist drug binds to the receptor, allowing ions to flow inward or outward Responses to activation of ligand-gated ion channels are fast, usually occurring in milliseconds