[The pharmacodynamic process: is the drug producing the required effect?]

Pharmacodynamics can be defined as the study of the biochemical and physiological effects of drugs and their mechanisms of action. The objectives of the analysis of drug action are to delineate the chemical or physical interactions between drug and target cell and to characterize the full sequence and scope of actions of each drug. The effects of most drugs result from their interaction with macromolecular components of the organism. These interactions alter the function of the pertinent component and thereby initiate the biochemical and physiological changes that are characteristic of the response to the drug. This concept, now obvious, had its origin in the experimental work of Ehrlich and Langley during the late nineteenth and early twentieth centuries. The term receptor was coined to denote the component of the organism with which the chemical agent was presumed to interact. The statement that the receptor for a drug can be any functional macromolecular component of the organism has several fundamental corollaries. One is that a drug potentially is capable of altering the rate at which any bodily function proceeds. Another is that drugs do not create effect, but instead modulate functions. The features of agonists and blockade by antagonists are also described.