Pharmacokinetics is defined as the study of the time course of drug absorption, distribution and elimination. The study of pharmacokinetics involves the mathematical analysis of drug concentration-time data in blood or other tissues which yields estimates of the rate and extent that drugs enter, distribute through and leave the body. Application of pharmacokinetic principles permits prediction of plasma drug concentrations over a dosing interval, calculation of dosage regimens, management of drug interactions and assessment of non-compliance. A knowledge of pharmacokinetic principles allows one to properly interpret AED concentration data and thus more accurately assign alterations in drug concentrations to non-compliance or other causes.