Drug clearance (CL)

Drug clearance relates the rate at which a drug is eliminated to a specified measured concentration:If elimination is 10 mg/h at a plasma concentration of 2 mg/L, clearance is 5 L/h. This is an effective volume per time, rather than the physical volume of fluid actually removed. The concentration reference, such as plasma or whole blood, must be specified. ^[ref]

For constant clearance and a one-compartment distribution volume $V$, the amount $A=VC$ obeys $dA/dt=-CLA/V$. Thus $k=CL/V$ and $t_{1/2}=V\ln 2/CL$. The derivation explains why a longer half-life can reflect greater distribution volume as well as lower clearance; half-life and clearance are not interchangeable measurements.