Clearance (medicine)

In medicine, the clearance is a pharmacokinetic measurement of the volume of plasma that is completely cleared off of a substance per unit time. The usual units are mL/min.

The total body clearance will be equal to the renal clearance + hepatic clearance + lung clearance. Although for many drugs the clearance is simply considered as the renal excretion ability, that is, the rate at which waste substances are cleared from the blood by the kidney. In these cases clearance is almost synonymous with renal clearance or renal plasma clearance. Each substance has a specific clearance that depends on its filtration characteristics. Clearance is a function of glomerular filtration, secretion from the peritubular capillaries to the nephron, and re-absorption from the nephron back to the peritubular capillaries. Clearance is variable in zero-order kinetics because a constant amount of the drug is eliminated per unit time, but it is constant in first-order kinetics, because the amount of drug eliminated per unit time changes with the concentration of drug in the blood. The concept of clearance was described by Thomas Addis, a graduate of the University of Edinburgh Medical School.