PK model structures for warfarin parent and metabolites. Dark blue frames: S-warfarin parent compound and metabolites models; dark red frames: R-warfarin parent compound and metabolites models. Cent, central; DR, drug-receptor complexes; M-Cent, metabolite central compartment; M-periph, metabolite peripheral compartment; M-urine, metabolite urine compartment; Periph, peripheral; R, receptors.