Figure 1.

A schematic overview of the one-compartment distribution model (a) and the extended-catenary biophase distribution model (b) to describe the biophase kinetics of morphine. The blood PKs were described with a three-compartment model and used as input function for morphine in the brain. The one-compartment distribution model consists of one effect compartment (e), whereas the biophase distribution model consists of two sequential compartments, the transfer (e_t) and the effect (e) compartment. The concentrations in the effect compartment were related to the EEG effect on the basis of the sigmoidal E_max model. In the figure, k_1e represents the rate constant for transport through the transfer compartment, k_eo represents the rate constant for loss from the effect compartment and is influenced by GF120918 and E_max represent the intrinsic activity and EC₅₀ represents the potency.