Fig. 2.

Schematic representation of the four tested structural models. f fraction of dose after absorption, D the dose, F _p fraction of parent reaching systemic circulation after absorption, K _ap absorption constant for the parent, K _am absorption constant for the metabolite, V _p volume of distribution for the parent, V _m volume of distribution for the metabolite, CL _po clearance of the parent by other pathways, CL _pm clearance of the parent into the metabolite, CL _mo clearance of the metabolite by other pathways, CL _mp clearance of back-transformation of the metabolite into the parent drug