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 Basic Features of the Dose-Response Relationship ● ● ● The dose-response relationship is graded, meaning that as the dosage increases, the response becomes larger Therapeutic effects can be adjusted by raising or lowering the dosage The dose-response relationship has three phases: phase 1 is characterized by low doses, phase 2 shows an increase in response with an increase in dose, and phase 3 involves a plateau in response Maximal Efficacy and Relative Potency ● ● ● Maximal efficacy is the largest effect that a drug can produce Relative potency refers to the strength of a drug compared to other drugs The dose-response curves for different drugs can show variations in maximal efficacy and relative potency Pharmacodynamics ● ● ● Pharmacodynamics is the study of the biochemical and physiological effects of drugs on the body and the molecular mechanisms by which those effects are produced It explores what drugs do to the body and how they do it Understanding pharmacodynamics is important for nurses to educate patients, make decisions about medication use, and evaluate drug effects Dose-Response Relationships ● ● The dose-response relationship shows the relationship between the administered dose and the intensity of the response produced It is a fundamental concept in pharmacology Dose-response relationships ● ● ● They determine the minimum amount of drug needed to elicit a response They determine the maximum response a drug can elicit They determine how much to increase the dosage to produce the desired increase in response Efficacy and potency ● ● ● ● A drug with very high maximal efficacy is not always more desirable than a drug with lower efficacy Efficacy is an index of the maximal response a drug can produce Potency is an index of how much drug must be administered to elicit a desired response Relative potency is indicated by the relative position of the dose-response curve along the x (dose) axis Drug Receptors ● ● Receptors are chemical sites in the body that drugs interact with to produce effects Receptors can be in the "ON" or "OFF" configuration ● Receptors are activated by interaction with other molecules