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 vloume/time.

The CLT 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. CLT 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).

The volume of distribution is the apparent volume in which the drug can be distributed in. It is the factor that relates the amount of drug in the body to the concentration of the drug in the sampling site. It is n. an actual volume, however it is a hypothetical volume determined by the dg distribution behavior.

The volume of distribution ranges from 3-5 liters to more than 25 L/kg. Drugs with higher affinity for tissues, have higher volume of distribution.

After drug administration drug molecules will spend different time intervals in the body despite the fact that all the molecules are similar. Some molecules will be eliminated very quickly and some will stay in the body for longer time based on the statistical probability.

The mean residence time is the average time that drug molecules stay in the body. The mean residence time has units of time