ABSTRACT
This chapter focuses on systemic medications, that is, pharmaceutical systems meant to deliver the active ingredient to systemic circulation from which it is transported by the blood to its molecular target at a given site of action. It reviews the simplest of the classical compartmental models: the one-compartment open model. An important principle to establish pharmacokinetic/pharmacodynamic relationships is the free drug hypothesis. The first part of the hypothesis, of enormous pharmacokinetic value, is verified whenever the stationary state is achieved provided that the drug transport across the biological membrane only involves passive diffusion. Pharmacokinetics is the study of absorption, distribution, and elimination from a quantitative point of view by studying the time course of drug concentration profiles in readily accessible body fluids, such as plasma, urine, or saliva, leading to understanding, interpretation, and prediction of concentration time profiles.
