title: Decreased Morphine Clearance in Neonates With Hypoxic Ischemic Encephalopathy Receiving Hypothermia.
abstract: Morphine is commonly used in neonates with hypothermic ischemic encephalopathy (HIE) during therapeutic hypothermia to provide comfort and analgesia. However, pharmacokinetic data to support morphine dosing in this vulnerable population are lacking. A prospective, 2-center clinical pharmacokinetic study of morphine was conducted in 20 neonates (birthweight, 1.82-5.3 kg) with HIE receiving hypothermia. Morphine dosing was per standard of care at each center. Morphine and glucuronide metabolites (morphine-3-glucuronide and morphine-6-gluronide) were measured via a validated dried blood spot liquid chromatography-tandem mass spectrometry assay. From the available concentration data (n = 106 for morphine; n = 106 for each metabolite), a population pharmacokinetic model was developed using nonlinear mixed-effects modeling. The clearance of morphine and glucuronide metabolites was best predicted by birthweight allometrically scaled using an exponent of 1.23. In addition, the clearance of each glucuronide metabolite was influenced by serum creatinine. No other significant predictors of clearance or volume of distribution were found. For a 3.5-kg neonate, morphine clearance was 0.77 L/h (CV, 48%), and the steady-state volume of distribution was 8.0 L (CV, 49%). Compared with previous studies in full-term newborns without HIE, morphine clearance was markedly lower. Dosing strategies customized for this vulnerable population will be needed. Applying the final population pharmacokinetic model, repeated Monte Carlo simulations (n = 1000 per simulation) were performed to evaluate various morphine dosing strategies that optimized achievement of morphine concentrations between 10 and 40 ng/mL. An optimized morphine loading dose of 50 μg/kg followed by a continuous infusion of 5 μg/kg/h was predicted across birthweights.
authors.affiliation: Department of Pediatrics, Stanford University, Palo Alto, CA, USA.
authors.forename: Adam
authors.initials: A
authors.lastname: Frymoyer
authors.affiliation: Department of Pediatrics, Stanford University, Palo Alto, CA, USA.
authors.forename: Sonia L
authors.initials: SL
authors.lastname: Bonifacio
authors.affiliation: Department of Anesthesiology, Perioperative and Pain Medicine, Palo Alto, CA, USA.
authors.forename: David R
authors.initials: DR
authors.lastname: Drover
authors.affiliation: Department of Pediatrics, Stanford University, Palo Alto, CA, USA.
authors.forename: Felice
authors.initials: F
authors.lastname: Su
authors.affiliation: Division of Child Neurology, Stanford University, Palo Alto, CA, USA.
authors.forename: Courtney J
authors.initials: CJ
authors.lastname: Wustoff
authors.affiliation: Department of Pediatrics, Stanford University, Palo Alto, CA, USA.
authors.forename: Krisa P
authors.initials: KP
authors.lastname: Van Meurs
mesh_terms: D061605:Administration, Intravenous; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007036:Hypothermia, Induced / Q000639:trends; D020925:Hypoxia-Ischemia, Brain / Q000097:blood* / Q000628:therapy*; D007231:Infant, Newborn; D008297:Male; D008657:Metabolic Clearance Rate / Q000187:drug effects* / Q000502:physiology*; D009020:Morphine / Q000008:administration & dosage / Q000097:blood*; D011446:Prospective Studies
chemical_list: D009020:Morphine
keywords: hypothermia; hypoxic ischemic encephalopathy; morphine; neonates; population pharmacokinetics