Examine the conc-time profiles after administration of the same dose of the drug when Vc is different. All other parameters are constant.
Please note that the change in Vc (the independent parameter) will be accompanied by change in the hybrid elimination rate constant (β, the dependent parameter) when the total body clearance is constant.
The increase in Vc will be accompanied by an increase in Vdss and Vdβ when all other parameters are kept constant.
Vcis the volume of the central compartment (volume).
αis the hybrid first-order rate constant for the distribution process (time-1).
Vdis the volume of distribution (volume).
Total body clearance (CLT)
The total body clearance is the volume of the plasma or blood that is completely cleared from the drug per unit time. It has units of volume/time. The total body clearance 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. total body clearance is the sum of the renal clearance, hepatic clearance and all other clearances).
The total body clearance and the volume of distribution (the independent parameters determine the elimination rate constant and the half life (the dependent parameters).
CLT
Vd = k
For one compartment model
CLT
Vc = k10
For two compartment model
Vdβis the volume of distribution during the elimination phase (volume).
CLTis the total body clearance (volume/time).
βis the hybrid first-order rate constant for the elimination process (time-1).
k10is the first-order elimination rate constant (time-1).
Vcis the volume of the central compartment (volume).
Vdssis the volume of distribution at steady state (volume).
Vcis the volume of the central compartment (volume).
k12is the first-order transfer rate constant from the central to the peripheral compartment (time-1).
k21is the first-order transfer rate constant from the peripheral to the central compartment (time-1).
