After iv administration of a drug the plasma concentration at any time can be expressed by the following relationship:

The AUC is the integral of plasma concentration from time zero to infinity. Integrating both sides of the equation:

and

So, the AUC after a single iv administration can be calculated from the initial plasma concentration and the elimination rate constant.

Since the AUC after iv administration is expressed as:

and

then

also,

The total body clearance is the volume of the plasma or blood which is completely cleared from the drug per unit time. It has units of volume/time.

The CL_T for a drug is constant within a patient (dose and concentration independent) when the elimination processes follow first-order kinetics.

The total body clearance is a measure of the efficiency of all eliminating organs in eliminating the drug and it is the sum of all organ clearances (i.e. CL_T is the sum of the renal clearance, hepatic clearance and all other organ clearances).

The elimination rate constant and the half life (the dependent pharmacokinetic parameters) are dependent on (is determined from) the total body clearance and the volume of distribution (the independent pharmacokinetic parameters).