
PK/PD modelling 147
FIGURE 6.3: (Artificial) PK/PD data illustrating hysteresis
The fact that we do not is a property called hysteresis. The word refers to
the history dependence of the system.
The purpose of PK/PD modelling is to be able to predict effect from plasma
concentrations. If we can do that, we can look for the optimal formulation
and dosage regimen of the drug which gives the best absorption profile so that
we find the effect profile we want. To achieve this, we need to find a method
or model that can account for the hysteresis and from which we can deduce a
model that predicts PD from PK.
The natural approach would be to use the differential equation ...