BACKGROUND AND PURPOSE: Biophase equilibration must be considered to gain insight into the mechanisms underlying the pharmacokinetic-pharmacodynamic (PK-PD) correlations of opioids. The objective was to characterise in a quantitative manner the non-linear distribution kinetics of morphine in brain. EXPERIMENTAL APPROACH: Male rats received a 10-min infusion of 4 mg kg(-1) of morphine, combined with a continuous infusion of the P-glycoprotein (Pgp) inhibitor GF120918 or vehicle, or 40 mg kg(-1) morphine alone. Unbound extracellular fluid (ECF) concentrations obtained by intracerebral microdialysis and total blood concentrations were analysed using a population modelling approach. KEY RESULTS: Blood pharmacokinetics of morphine was best described with a three-compartment model and was not influenced by GF120918. Non-linear distribution kinetics in brain ECF was observed with increasing dose. A one compartment distribution model was developed, with separate expressions for passive diffusion, active saturable influx and active efflux by Pgp. The passive diffusion rate constant was 0.0014 min(-1). The active efflux rate constant decreased from 0.0195 min(-1) to 0.0113 min(-1) in the presence of GF120918. The active influx was insensitive to GF120918 and had a maximum transport (N(max)/V(ecf)) of 0.66 ng min(-1) ml(-1) and was saturated at low concentrations of morphine (C(50)=9.9 ng ml(-1)). CONCLUSIONS AND IMPLICATIONS: Brain distribution of morphine is determined by three factors: limited passive diffusion; active efflux, reduced by 42% by Pgp inhibition; low capacity active uptake. This implies blood concentration-dependency and sensitivity to drug-drug interactions. These factors should be taken into account in further investigations on PK-PD correlations of morphine.
BACKGROUND AND PURPOSE: Biophase equilibration must be considered to gain insight into the mechanisms underlying the pharmacokinetic-pharmacodynamic (PK-PD) correlations of opioids. The objective was to characterise in a quantitative manner the non-linear distribution kinetics of morphine in brain. EXPERIMENTAL APPROACH: Male rats received a 10-min infusion of 4 mg kg(-1) of morphine, combined with a continuous infusion of the P-glycoprotein (Pgp) inhibitor GF120918 or vehicle, or 40 mg kg(-1) morphine alone. Unbound extracellular fluid (ECF) concentrations obtained by intracerebral microdialysis and total blood concentrations were analysed using a population modelling approach. KEY RESULTS: Blood pharmacokinetics of morphine was best described with a three-compartment model and was not influenced by GF120918. Non-linear distribution kinetics in brain ECF was observed with increasing dose. A one compartment distribution model was developed, with separate expressions for passive diffusion, active saturable influx and active efflux by Pgp. The passive diffusion rate constant was 0.0014 min(-1). The active efflux rate constant decreased from 0.0195 min(-1) to 0.0113 min(-1) in the presence of GF120918. The active influx was insensitive to GF120918 and had a maximum transport (N(max)/V(ecf)) of 0.66 ng min(-1) ml(-1) and was saturated at low concentrations of morphine (C(50)=9.9 ng ml(-1)). CONCLUSIONS AND IMPLICATIONS: Brain distribution of morphine is determined by three factors: limited passive diffusion; active efflux, reduced by 42% by Pgp inhibition; low capacity active uptake. This implies blood concentration-dependency and sensitivity to drug-drug interactions. These factors should be taken into account in further investigations on PK-PD correlations of morphine.
Authors: J Bengtsson; P Ederoth; D Ley; S Hansson; I Amer-Wåhlin; L Hellström-Westas; K Marsál; C-H Nordström; M Hammarlund-Udenaes Journal: Br J Pharmacol Date: 2009-05-11 Impact factor: 8.739
Authors: R Clinckers; I Smolders; Y Michotte; G Ebinger; M Danhof; R A Voskuyl; O Della Pasqua Journal: Br J Pharmacol Date: 2008-10-06 Impact factor: 8.739