• Elke H J Krekels, Dick Tibboel, Saskia N de Wildt, Ilse Ceelie, Albert Dahan, Monique van Dijk, Meindert Danhof, and Catherijne A J Knibbe.
• Division of Pharmacology, Leiden Academic Center for Drug Research, Leiden University, Leiden, The Netherlands.
• Clin Pharmacokinet. 2014 Jun 1;53(6):553-63.

Background And ObjectivesFrom a previously validated paediatric population pharmacokinetic model, it was derived that non-linear morphine maintenance doses of 5 μg/kg(1.5)/h, with a 50 % dose reduction in neonates with a postnatal age (PNA) <10 days, yield similar morphine and metabolite concentrations across patients younger than 3 years. Compared with traditional dosing, this model-derived dosing regimen yields significantly reduced doses in neonates aged <10 days.MethodsConcentration predictions of the population model were prospectively evaluated in postoperative term neonates and infants up to the age of 1 year who received morphine doses according to the model-derived algorithm. The efficacy of this dosing algorithm was evaluated using morphine rescue medication and actual average infusion rates.ResultsMorphine and metabolite concentrations were accurately predicted by the paediatric pharmacokinetic morphine model. With regard to efficacy, 5 out of 18 neonates (27.8 %) with a PNA of <10 days needed rescue medication versus 18 of the 20 older patients (90 %) (p = 0.06). The median (interquartile range [IQR]) total morphine rescue dose was 0 (0-20) μg/kg in younger patients versus 193 (19-362) μg/kg in older patients (p = 0.003). The median (IQR) actual average morphine infusion rate was 4.4 (4.0-4.8) μg/kg/h in younger patients versus 14.4 (11.3-23.4) μg/kg/h in older patients (p < 0.001).ConclusionMorphine paediatric dosing algorithms corrected for pharmacokinetic differences alone yield effective doses that prevent over-dosing for neonates with a PNA <10 days. The fact that many neonates and infants with a PNA ≥10 days still required rescue medication warrants pharmacodynamic studies to further optimize the dosing algorithm for these patients.

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