Pharmacokinetics is the study of drug absorption, distribution, metabolism, and excretion. A fundamental concept in pharmacokinetics is drug clearance, that is, elimination of drugs from the body, analogous to the concept of creatinine clearance. AUC, the area under the curve, represents the total drug exposure integrated over time and is an important parameter for both pharmacokinetic and pharmacodynamic analyses. As indicated in the clearance is simply the ratio of the dose to the AUC, so that the higher the AUC for a given dose, the lower the clearance. If a drug is administered by continuous infusion and a steady state is achieved, the clearance can be estimated from a single measurement of the plasma drug concentration (Css). Clearance can conceptually be considered to be a function of both distribution and elimination. In the simplest pharmacokinetic model.
