ABSTRACT
This chapter describes the characteristics of tolerance for each class of drugs and reviews the mechanisms which conceivably could underlie the various phenomena of tolerance. Drug tolerance is a very broad subject involving a large number of substances from a variety of pharmacological classes. It is part of the even broader topic of adaptation to change in the environment. Drug refers to any chemical or substance used to produce an alteration or response in a biological system. There are several quantitative characteristics of tolerance, which collectively provide a basis for: accurately defining the specific phenomenon under consideration, determining the factors which influence tolerance development and correlating physiological and biochemical alterations with changes in tolerance in the hope of identifying the mechanisms responsible for tolerance phenomena. Excretory processes which involve simple physical diffusion depend primarily on the concentration of the free drug in plasma.
