<P> In the field of pharmacokinetics, the area under the curve (AUC) is the area under the curve (mathematically known as the definite integral) in a plot of drug concentration in blood plasma vs. time . In practice, the drug concentration is measured at certain discrete points in time and the trapezoidal rule is used to estimate AUC . </P> <P> The AUC (from zero to infinity) represents the total drug exposure over time . Assuming linear pharmacodynamics with elimination rate constant K, one can show that AUC is proportional to the total amount of drug absorbed by the body . The proportionality constant is 1 / K . </P> <P> This is useful when trying to determine whether two formulations of the same dose (for example a capsule and a tablet) release the same dose of drug to the body . Another use is in the therapeutic drug monitoring of drugs with a narrow therapeutic index . For example, gentamicin is an antibiotic that can be nephrotoxic (kidney damaging) and ototoxic (hearing damaging); measurement of gentamicin trough concentrations in a patient's plasma and calculation of the AUC is used to guide the dosage of this drug . </P>

What does the area under the curve show