Pharmacodynamic Analysis of Morphine Time to Remedication Events in Infants and Young Children After Congenital Heart Surgery
ObjectiveThe aim of this study was to characterize the relationship between morphine plasma concentration and repeated time to postoperative remedication events in children undergoing cardiac surgery.MethodsData from our previously published study of morphine pharmacokinetics were utilized in this pharmacodynamic study. A population survival analysis based on hazard functions was undertaken in NONMEM(r).ResultsHazard was best described by a Gompertz function changing in steps over time. Concentration and age were the only predictors of the hazard function. Concentration producing 50 reduction in hazard was 19.6 (bootstrap 95 confidence interval 5.90 49.5 ng/ml) The hazard ratio for a 1 year old child to a 1 month old child was 1.91 (1.35 2.86) Sensitivity to morphine decreased with age and leveled off after 1 year of life. Morphine sulfate doses >0.1 mg/kg did not noticeably increase tolerable pain durations.ConclusionTime to remedication is a clinically useful endpoint for assessing opioid induced analgesia. Sensitivity to morphine treatment is age dependent. Morphine sulfate doses of 0.1 0.2 mg/kg are adequate for the management of postoperative pain in children. Our findings may help avoid unnecessary large morphine doses in children.
Clinical Pharmacokinetics