Chapter 19 - Time Course of Drug Response

Abstract

This chapter reviews the time course of drug response. Therapeutic drug responses are a consequence of drug exposure. Exposure describes the intensity and time course of drug treatment. The reasons for elaborating the time course of drug response give rise to two basic conceptual approaches for describing the delay between plasma concentrations and changes in physiological effect. In the first approach, the effect is considered a direct consequence of drug action and the delay is thought to reflect the time required for the drug to reach its site of pharmacologic action. In the second approach, the drug is thought to alter the synthesis or degradation of some factor, usually an endogenous compound that mediates the physiological effect. The models that are used to relate steady-state plasma concentrations of drug to observed effects can also be applied to the time course of drug effects. In addition to delays in drug effect because of pharmacokinetic (PK) distribution to the site of action, there are delays determined by the turnover of these effect mediators. The time course of the physiological mediator can be thought of as an example of physiokinetics. The therapeutic response, cumulative drug effects, and schedule dependence are also elaborated in the chapter.