Abstract
This chapter describes pharmacodynamics, which encompasses the actions of drugs on the body that produce a drug effect. The primary focus is on the cellular and molecular mechanisms of these important drug actions. Most drugs act on receptors, which are proteins or other components of cells, to produce their effects. We illustrate five major classes of receptors: G protein–coupled receptors, ion channel–linked receptors, transmembrane receptors with intrinsic enzymatic function, transmembrane receptors that activate a cytosolic enzyme, and intracellular receptors that affect DNA transcription. The mechanisms through which these receptor classes activate their canonical intracellular signaling pathways are discussed. Quantitative information related to describing the drug-receptor interaction and the concentration-response relationship is described and the concepts of drug affinity, potency, and intrinsic activity are also illustrated. These drug parameters are further related to drugs classified as full agonists, partial agonists, inverse agonists, competitive antagonists, and noncompetitive antagonists. Tolerance to drug effects is also discussed in the context of receptor desensitization and downregulation. Drug actions involving various nonreceptor mechanisms are also briefly reviewed.