Mechanisms of Drug Action

Abstract

Pharmacodynamics is the study of the biological effect of drugs on biological tissues and organs and the mechanism of action. While there are some exceptions, the general rule is that drugs do not work unless they bind to a receptor. A receptor is a cellular component that the drugs bind to and produce cellular action. Receptors can either be signal-transducing extracellular entities, ion channels, intracellular enzymes or intranuclear targets. Drug molecules require affinity to bind to a receptor and intrinsic activity to activate them and cause downstream signaling. The broad types of drugs that bind to the receptor are agonists, partial agonists, antagonists and inverse agonists. The effect of a drug at varying dose ranges is studied by plotting a dose-response curve. The dose-response relationship helps us in identifying the most potent and efficacious drug for a particular clinical response. Based on the site at which the drugs act and their intrinsic activity, drugs can interact with each other to cause additive or antagonistic effects. Receptors being stimulated or blocked for a long time undergo downregulation or upregulation, respectively. Various host and drug factors affect the pharmacodynamic action of drugs.