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 Antagonists ● ● ● Antagonists prevent receptor activation by endogenous regulatory molecules and drugs They have affinity for a receptor but no intrinsic activity They can produce pharmacologic effects Types of antagonists: ● ● Competitive antagonists Noncompetitive antagonists Effects of antagonists: ● ● Antagonists prevent the activation of receptor molecules by agonists By blocking the actions of agonists, antagonists can produce beneficial effects ● Antagonists can also block the actions of endogenous regulatory molecules or drugs Response to antagonists: ● ● ● The response to an antagonist is determined by the presence of agonist molecules If there is no agonist present, administration of an antagonist will have no observable effect If receptors are already activated by agonists, administration of an antagonist will shut down the process and result in an observable response Partial agonists: ● ● ● Partial agonists have moderate intrinsic activity They can act as both antagonists and agonists Pentazocine is an example of a partial agonist Types of antagonists: ● ● Noncompetitive antagonists Competitive antagonists Noncompetitive antagonists: ● Noncompetitive antagonists decrease the maximal response achievable with an agonist Competitive antagonists: ● Competitive antagonists increase the amount of agonist required to produce a given intensity of response Interpatient variability in drug responses ● ● ● Patients differ from one another in their response to medication It is not possible to predict exactly how an individual patient will respond to a drug Interpatient variation must be taken into account when determining the appropriate dosage or treatment