total body clearance

If several drains are emptying one bathtub at the same time, the total rate the tub empties is just the sum of all the drains. Total body clearance is exactly that idea for a drug: the combined cleaning power of every organ that removes it, added together into a single number.

Formally, total body clearance is the volume of plasma completely cleared of drug per unit time by all routes at once. It equals renal clearance plus hepatic clearance plus any other contributions such as lung or biliary clearance. Because the organs work in parallel, the clearances simply add.

This single value is one of the most useful in pharmacokinetics because it ties the dose to the steady-state concentration: at steady state, the rate the drug goes in must equal clearance times concentration. It also links to half-life through the volume of distribution, so clearance and volume together determine how long a drug lingers and how often it must be dosed.