Let’s say you know a bioexponential equation modeling the presence of drug in the serum, such that Cp=Ae^(-at)+Be^(bt). a = k12 and b = k21.
To calculate the volume of the central compartment:
Note that at t=0, Cp_initial. The intial Drug dose, Do, divided by Cp_o is the volume of the plasma compartment or the central compartment volume.
To calculate the tissue compartment volume:
Vt = Vp*k12/k21
Refer to the following page for calculating k12 an k21:
Pharmacokinetics – multi-compartment models – method of residuals, intercepts and slopes
Calculating the half-life of the elimination phase from the central compartment:
t1/2 = ln(2)/k12.
Calculating the half-life of the elimination phase from the tissue compartment:
t1/2 = ln(2)/k21.
Why are we not directly sampling the tissue for drug concentrations?