ABSTRACT
This chapter lays down the conceptual framework for understanding the quantitative and temporal aspects of drug-drug interactions, hereafter called drug interactions for simplicity. Some pharmacodynamic aspects are also covered, however, for there are many similarities between pharmacokinetic and pharmacodynamic interactions at the molecular level and because ultimately one has to place a pharmacokinetic interaction into a pharmacodynamic perspective to appreciate the likely therapeutic impact. Pharmacokinetic information gained following single-dose administration can be used to help predict the likely events following chronic dosing, either as a constant-rate infusion or multiple dosing, which often involves giving a fixed dose at set time intervals. Practically all drug interactions are graded, being dependent on the concentrations of the interacting drugs and, hence, on their pharmacokinetics as well as manner of administration. There are a whole variety of factors that further complicate both the interpretation and quantitative prediction of the pharmacokinetic aspects of drug interactions.
