Background and purpose:At present there are few data regarding the rate and extent of brain–blood partitioning of the opioid active metabolite of morphine, morphine-6-glucuronide (M6G). In this study the cerebral kinetics of M6G were...
moreBackground and purpose:At present there are few data regarding the rate and extent of brain–blood partitioning of the opioid active metabolite of morphine, morphine-6-glucuronide (M6G). In this study the cerebral kinetics of M6G were determined, after a short-term intravenous infusion, in chronically instrumented conscious sheep.At present there are few data regarding the rate and extent of brain–blood partitioning of the opioid active metabolite of morphine, morphine-6-glucuronide (M6G). In this study the cerebral kinetics of M6G were determined, after a short-term intravenous infusion, in chronically instrumented conscious sheep.Experimental approach:Five sheep received an intravenous infusion of M6G 2.2 mg kg-1 over a four-minute period. Non-linear mixed-effects analysis, with hybrid physiologically based kinetic models, was used to estimate cerebral kinetics from the arterio-sagittal sinus concentration gradients and cerebral blood flow measurements.Five sheep received an intravenous infusion of M6G 2.2 mg kg-1 over a four-minute period. Non-linear mixed-effects analysis, with hybrid physiologically based kinetic models, was used to estimate cerebral kinetics from the arterio-sagittal sinus concentration gradients and cerebral blood flow measurements.Key results:A membrane limited model was selected as the final model. The blood-brain equilibration of M6G was relatively slow (time to reach 50% equilibration of the deep compartment 5.8 min), with low membrane permeability (PS, population mean, 2.5 ml min-1) from the initial compartment (V1, 13.7 ml) to a small deep distribution volume (V2) of 18.4 ml. There was some between-animal variability (%CV) in the initial distribution volume (29%), but this was not identified for PS or V2.A membrane limited model was selected as the final model. The blood-brain equilibration of M6G was relatively slow (time to reach 50% equilibration of the deep compartment 5.8 min), with low membrane permeability (PS, population mean, 2.5 ml min-1) from the initial compartment (V1, 13.7 ml) to a small deep distribution volume (V2) of 18.4 ml. There was some between-animal variability (%CV) in the initial distribution volume (29%), but this was not identified for PS or V2.Conclusion and Implications:Pharmacokinetic modelling of M6G showed a delayed equilibration between brain and blood of a nature that is primarily limited by permeability across the blood-brain-barrier, in accordance with its physico-chemical properties.British Journal of Pharmacology (2006) 149, 754–760. doi:10.1038/sj.bjp.0706916Pharmacokinetic modelling of M6G showed a delayed equilibration between brain and blood of a nature that is primarily limited by permeability across the blood-brain-barrier, in accordance with its physico-chemical properties.British Journal of Pharmacology (2006) 149, 754–760. doi:10.1038/sj.bjp.0706916
