- Drugs with larger CLT are eliminated faster (if Vd is similar) and will have smaller AUC (if the administered dose is similar).
- Administration of the same dose of different drugs result in the formation of the same amount of metabolite if the fraction of the drug converted to the metabolite (fm) is constant. However the metabolite formation rate will be faster for the drugs with higher clearance.
- Since the metabolite parameters are similar and the same amount of metabolite is formed in vivo, the metabolite AUC will be the same regardless of the parent drug AUC
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 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).
CLT
Vd = k andCLT
Vd =0.693
t 1/2