One-compartment pharmacokinetic model

Abstract

The one-compartment pharmacokinetic model is the simplest compartmental pharmacokinetic model. As the name suggests, the model considers the whole organism as a single compartment where the drug distributes homogeneously and instantaneously, an extreme simplification that leads to a very simple mathematical description. The assumption of instantaneous and homogeneous distribution also implies that the apparent volume of distribution (Vd) will be constant. Another second and very important assumption of the model is that drug elimination within the compartment occurs following (apparent) firstorder kinetics (Fig. 1). Depending on the modeled therapeutic scenario, drug absorption will be assumed to be instantaneous (intravenous bolus), or to follow zero or first-order kinetics (intravenous infusion at a constant rate or extravascular drug administration, respectively). The model has considerable didactic importance, and, despite its many shortcomings, it is able to properly fit the pharmacokinetic data of some drugs. By solving the correspondent mass balance, it is possible to obtain equations of drug amount in the body (A) versus time t, or concentration within the compartment (equivalent, here, to plasma concentration, Cp) versus t.