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 The four primary receptor families ● ● The four primary receptor families are cell membrane-embedded enzymes, ligand-gated ion channels, G protein-coupled receptor systems, and transcription factors These families are involved in regulating various cellular processes G protein-coupled receptors ● ● ● Span the cell membrane and have a ligand-binding domain on the cell surface Receptors interact with endogenous ligands and agonist drugs Activation of these receptors stimulates cellular responses Transcription factors ● ● ● Found within the cell nucleus Regulate protein synthesis by binding to DNA Activation of these receptors is delayed and can take hours or days Receptor specificity ● ● ● Receptors have specific requirements for ligand binding Drugs can be designed to selectively interact with specific receptor types Endogenous ligands that act through transcription factors include thyroid hormone and steroid hormones Selectivity of drug action ● ● Selectivity is desirable in drugs to elicit specific responses If a single receptor type regulates multiple processes, drugs that interact with that receptor can influence multiple processes Selective drug action and receptor specificity ● ● ● ● ● ● The fewer opioid receptors a drug interacts with, the fewer side effects it will produce Drugs act through specific receptors, allowing for selective drug action Morphine, for example, is selective for one class of receptors but can still produce varied effects such as respiratory depression and constipation The body has different kinds of receptors for neurotransmitters, hormones, and other molecules it uses to regulate physiological processes Each type of receptor participates in the regulation of multiple processes Receptor selectivity does not guarantee safety; a highly selective compound like botulinum toxin can still be dangerous Theories of drug-receptor interaction ● ● ● ● The simple occupancy theory suggests that a drug interacts with a receptor by occupying it The modified occupancy theory considers two qualities of drugs: affinity and intrinsic activity A drug's affinity refers to the strength of attraction between the drug and its receptor Intrinsic activity refers to the drug's ability to activate the receptor after binding ● ● A drug's affinity determines its potency, with high affinity drugs being strongly attracted to their receptors A drug's intrinsic activity is independent of its affinity