<P> In pharmacology, the clearance is a pharmacokinetic measurement of the volume of plasma from which a substance is completely removed per unit time; the usual units are mL / min . The quantity reflects the rate of drug elimination divided by plasma concentration . </P> <P> 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 . </P> <P> It can refer to the amount of drug removed from the whole body per unit time, or in some cases the inter-compartmental clearances can be discussed referring to redistribution between body compartments such as plasma, muscle, fat . </P>

How to calculate the clearance of a drug