Pharmacokinetics of Morphine and Its Metabolites in Infants and Young Children After Congenital Heart Surgery

Remimazolam anesthesia in pediatric patients undergoing cardiac catheterization for congenital heart disease: a retrospective observational study

BACKGROUND

Benzodiazepines are used in pediatric patients with congenital heart disease (CHD) because of their mild hemodynamic depressant effects. A novel short-acting benzodiazepine, remimazolam, is expected to be suitable for these patients. We examined the characteristics of remimazolam anesthesia in pediatric patients with CHD undergoing cardiac catheterization.

METHODS

This single-center retrospective study included pediatric patients undergoing cardiac catheterization for CHD. The primary outcome was the remimazolam dose for loss of consciousness. Secondary outcomes included the mean maintenance remimazolam dose, recovery time from anesthesia, predicted remimazolam concentration at emergence, decrease in blood pressure and heart rate, vasopressor administration during anesthesia, electroencephalogram index (bispectral index: BIS or patient state index: PSI), and life-threatening adverse events.

RESULTS

Thirty-nine patients, aged 2 months to 16 years, were included. Thirty-three patients received a median [interquartile] midazolam dose of 0.10 [0.10-0.10] mg.kg-1 in the pre-anesthesia room. The remimazolam dose for loss of consciousness was 0.34 [0.26-0.45] mg.kg-1. The mean maintenance dose was 1.0 [0.8-1.4] mg.kg-1.h-1. The recovery time was 15 [12-17] min. The predicted remimazolam concentration at emergence was 0.4-1.2 µg.ml-1 in 3-6-year-old patients. Blood pressure and heart rate decreased by 30% in 15 and 6 patients, respectively. Vasopressors were administered as a bolus in 8 patients. The BIS or PSI did not fall ≤ 60 or ≤ 50, respectively, in 51% of patients before tracheal intubation. No life-threatening adverse events were reported.

CONCLUSIONS

Remimazolam is a good alternative anesthetic agent for pediatric patients undergoing cardiac catheterization for CHD.

Possible unusual presentation of opioid side effect in a child: a case report

Atypical presentations are commonly encountered in the Pediatric intensive care unit (PICU) but having a high index of suspicion is crucial to prevent or treat severe and life-threatening conditions. This case describes the clinical presentation and course of a 14-month-old girl with congenital heart disease who was admitted to the PICU after cardiac repair and remained agitated, irritable, in hysteria and delirium despite adequate sedation. Different measures to relieve her condition were attempted but to no avail. All the common causes of this atypical presentation including pain, ventilator induced agitation, low cardiac output syndrome (LCOS), opioid side effects, toxicity, opioid induced neurotoxicity (OIN) as well as withdrawal syndrome were ruled out. However, the use of naloxone as a last resort after exhausting all the other options has led to immediate and successful reversal of her symptoms.

Management of routine postoperative pain for children undergoing cardiac surgery: a Paediatric Acute Care Cardiology Collaborative Clinical Practice Guideline

BACKGROUND

Pain following surgery for cardiac disease is ubiquitous, and optimal management is important. Despite this, there is large practice variation. To address this, the Paediatric Acute Care Cardiology Collaborative undertook the effort to create this clinical practice guideline.

METHODS

A panel of experts consisting of paediatric cardiologists, advanced practice practitioners, pharmacists, a paediatric cardiothoracic surgeon, and a paediatric cardiac anaesthesiologist was convened. The literature was searched for relevant articles and Collaborative sites submitted centre-specific protocols for postoperative pain management. Using the modified Delphi technique, recommendations were generated and put through iterative Delphi rounds to achieve consensus.

RESULTS

60 recommendations achieved consensus and are included in this guideline. They address guideline use, pain assessment, general considerations, preoperative considerations, intraoperative considerations, regional anaesthesia, opioids, opioid-sparing, non-opioid medications, non-pharmaceutical pain management, and discharge considerations.

CONCLUSIONS

Postoperative pain among children following cardiac surgery is currently an area of significant practice variability despite a large body of literature and the presence of centre-specific protocols. Central to the recommendations included in this guideline is the concept that ideal pain management begins with preoperative counselling and continues through to patient discharge. Overall, the quality of evidence supporting recommendations is low. There is ongoing need for research in this area, particularly in paediatric populations.

Postoperative breakthrough pain in paediatric cardiac surgery not reduced by increased morphine concentrations

BACKGROUND

Morphine is commonly used for postoperative analgesia in children. Here we studied the pharmacodynamics of morphine in children after cardiac surgery receiving protocolized morphine.

METHODS

Data on morphine rescue requirements guided by validated pain scores in children (n = 35, 3-36 months) after cardiac surgery receiving morphine as loading dose (100 μg kg^-1) with continuous infusion (40 μg kg^-1 h^-1) from a previous study on morphine pharmacokinetics were analysed using repeated time-to-event (RTTE) modelling.

RESULTS

During the postoperative period (38 h (IQR 23-46)), 130 morphine rescue events (4 (IQR 1-5) per patient) mainly occurred in the first 24 h (107/130) at a median morphine concentration of 29.5 ng ml^-1 (range 7-180 ng ml^-1). In the RTTE model, the hazard of rescue morphine decreased over time (half-life 18 h; P < 0.001), while the hazard for rescue morphine (21.9% at 29.5 ng ml^-1) increased at higher morphine concentrations (P < 0.001).

CONCLUSIONS

In this study on protocolized morphine analgesia in children, rescue morphine was required at a wide range of morphine concentrations and further increase of the morphine concentration did not lead to a decrease in hazard. Future studies should focus on a multimodal approach using other opioids or other analgesics to treat breakthrough pain in children.

IMPACT

In children receiving continuous morphine infusion, administration of rescue morphine is an indicator for insufficient effect or an event. Morphine rescue events were identified at a wide range of morphine concentrations upon a standardized pain protocol consisting of continuous morphine infusion and morphine as rescue boluses. The expected number of rescue morphine events was found to increase at higher morphine concentrations. Instead of exploring more aggressive morphine dosing, future research should focus on a multimodal approach to treat breakthrough pain in children.

Pediatric Cardiac Surgery and Pain Management: After 40 Years in the Desert, Have We Reached the Promised Land?

Pain prevention in the pediatric population is mandatory and an integrative aspect of medical practice. Optimal pain management is the right of all patients and the responsibility of all health professionals. The key to adequate pain management is assessing its presence and severity, identifying those who require intervention, and appreciating treatment efficacy. The population of pediatric patients undergoing cardiac surgery is unique in both clinical severity and hemodynamic response to painful stimuli, thus making pain management even more challenging. In this review, we will describe the different pain assessment tools as well as intra- and postoperative regimens of pain management.

Pharmacokinetic considerations for pediatric patients receiving analgesia in the intensive care unit; targeting postoperative, ECMO and hypothermia patients

INTRODUCTION

Adequate postoperative analgesia in pediatric patients in the intensive care unit (ICU) matters, since untreated pain is associated with negative outcomes. Compared to routine postoperative patients, children undergoing hypothermia (HT) or extracorporeal membrane oxygenation (ECMO), or recovering after cardiac surgery likely display non-maturational differences in pharmacokinetics (PK) and pharmacodynamics (PD). These differences warrant additional dosing recommendations to optimize pain treatment. Areas covered: Specific populations within the ICU will be discussed with respect to expected variations in PK and PD for various analgesics. We hereby move beyond maturational changes and focus on why PK/PD may be different in children undergoing HT, ECMO or cardiac surgery. We provide a stepwise manner to develop PK-based dosing regimens using population PK approaches in these populations. Expert opinion: A one-dose to size-fits-all for analgesia is suboptimal, but for several commonly used analgesics the impact of HT, ECMO or cardiac surgery on average PK parameters in children is not yet sufficiently known. Parameters considering both maturational and non-maturational covariates are important to develop population PK-based dosing advices as part of a strategy to optimize pain treatment.

Endogenous Opiates and Behavior: 2016

This paper is the thirty-ninth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2016 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Drug metabolism in early infancy: opioids as an illustration

INTRODUCTION

Drug dosing in infants frequently depends on body weight as a crude indicator for maturation. Fentanyl (metabolized by Cytochrome P450 3A4) and morphine (glucuronidated by UDP-glucuronosyltransferase-2B7) served as model drugs to provide insight in maturation patterns of these enzymes and provide understanding of the impact of non-maturational factors to optimize dosing in infants. Areas covered: Systematic searches on metabolism and population pharmacokinetic (Pop-PK) models for fentanyl and morphine were performed. Pre- and post-model selection criteria were applied to assess and evaluate the validity of these models. It was observed that maturational changes have been rather well investigated, be it with variability in the maturational function estimates. The same holds true for Pop-PK models, where non-maturational covariates have also been reported (pharmacogenetics, disease state or external influences), although less incorporated in the PK models and with limited knowledge on mechanisms involved. Expert opinion: PK models for fentanyl and morphine are currently available. Consequently, we suggest that researchers should not continue to develop new models, but should investigate whether collected data fit in already existing models and provide additional value concerning the impact of (non)-maturational factors like drug-drug interactions or pharmacogenetics.

Non-maturational covariates for dynamic systems pharmacology models in neonates, infants, and children: Filling the gaps beyond developmental pharmacology

Pharmacokinetics and -dynamics show important changes throughout childhood. Studies on the different maturational processes that influence developmental pharmacology have been used to create population PK/PD models that can yield individualized pediatric drug dosages. These models were subsequently translated to semi-physiologically or physiology-based PK (PBPK) models that support predictions in pediatric patient cohorts and other special populations. Although these translational efforts are crucial, these models should be further improved towards individual patient predictions by including knowledge on non-maturational covariates. These efforts are needed to ultimately get to systems pharmacology models for children. These models take developmental changes relating to the pediatric dynamical system into account but also other aspects that may be of importance such as abnormal body composition, pharmacogenetics, critical illness and inflammatory status.

Pharmacodynamic Analysis of Morphine Time-to-Remedication Events in Infants and Young Children After Congenital Heart Surgery

OBJECTIVE

The 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.

METHODS

Data 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(®).

RESULTS

Hazard 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.

CONCLUSION

Time 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.

Decreased Morphine Clearance in Neonates With Hypoxic Ischemic Encephalopathy Receiving Hypothermia

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.