Fig. 5. (  A ) Graphs of the ratio of measured to predicted drug concentrations  versus time relations for  S -(+)- and  R -(−)-ketamine in all five dogs. Predicted concentrations are from the ketamine models in which Cl^Eis modeled from the arterial sampling site (central) and all distribution parameters are adjusted independently (model 1). (  B ) Graphs of the ratio of measured to predicted drug concentrations  versus time relations for  S -(+)- and  R -(−)-ketamine in all five dogs. Predicted concentrations are from the ketamine models in which Cl^Eis modeled from the rapidly equilibrating peripheral tissue compartment (peripheral) and all distribution parameters are adjusted such that they are the same for the  S -(+)- and  R -(−)-enantiomers (model 4).