Morphine pharmacokinetics and pharmacodynamics in preterm and term neonates: secondary results from the NEOPAIN trial

Institutional and Regional Variation in Opioid Prescribing for Hospitalized Infants in the US

Importance

High-risk infants, defined as newborns with substantial neonatal-perinatal morbidities, often undergo multiple procedures and require prolonged intubation, resulting in extended opioid exposure that is associated with poor outcomes. Understanding variation in opioid prescribing can inform quality improvement and best-practice initiatives.

Objective

To examine regional and institutional variation in opioid prescribing, including short- and long-acting agents, in high-risk hospitalized infants.

Design, Setting, and Participants

This retrospective cohort study assessed high-risk infants younger than 1 year from January 1, 2016, to December 31, 2022, at 47 children's hospitals participating in the Pediatric Health Information System (PHIS). The cohort was stratified by US Census region (Northeast, South, Midwest, and West). Variation in cumulative days of opioid exposure and methadone treatment was examined among institutions using a hierarchical generalized linear model. High-risk infants were identified by International Statistical Classification of Diseases and Related Health Problems, Tenth Revision codes for congenital heart disease surgery, medical and surgical necrotizing enterocolitis, extremely low birth weight, very low birth weight, hypoxemic ischemic encephalopathy, extracorporeal membrane oxygenation, and other abdominal surgery. Infants with neonatal opioid withdrawal syndrome, in utero substance exposure, or malignant tumors were excluded.

Exposure

Any opioid exposure and methadone treatment.

Main Outcomes and Measures

Regional and institutional variations in opioid exposure.

Results

Overall, 132 658 high-risk infants were identified (median [IQR] gestational age, 34 [28-38] weeks; 54.5% male). Prematurity occurred in 30.3%, and 55.3% underwent surgery. During hospitalization, 76.5% of high-risk infants were exposed to opioids and 7.9% received methadone. Median (IQR) length of any opioid exposure was 5 (2-12) cumulative days, and median (IQR) length of methadone treatment was 19 (7-46) cumulative days. There was significant hospital-level variation in opioid and methadone exposure and cumulative days of exposure within each US region. The computed intraclass correlation coefficient estimated that 16% of the variability in overall opioid prescribing and 20% of the variability in methadone treatment was attributed to the individual hospital.

Conclusions and Relevance

In this retrospective cohort study of high-risk hospitalized infants, institution-level variation in overall opioid exposure and methadone treatment persisted across the US. These findings highlight the need for standardization of opioid prescribing in this vulnerable population.

Non-pharmacological interventions for the prevention of pain during endotracheal suctioning in ventilated neonates

BACKGROUND

Pain, when treated inadequately, puts preterm infants at a greater risk of developing clinical and behavioural sequelae because of their immature pain system. Preterm infants in need of intensive care are repeatedly and persistently exposed to noxious stimuli, and this happens during a critical window of their brain development with peak rates of brain growth, exuberant synaptogenesis and the developmental regulation of specific receptor populations. Nearly two-thirds of infants born at less than 29 weeks' gestation require mechanical ventilation for some duration during the newborn period. These neonates are endotracheally intubated and require repeated endotracheal suctioning. Endotracheal suctioning is identified as one of the most frequent and most painful procedures in premature infants, causing moderate to severe pain. Even with improved nursing performance and standard procedures based on neonatal needs, endotracheal suctioning remains associated with mild pain.

OBJECTIVES

To evaluate the benefits and harms of non-pharmacological interventions for the prevention of pain during endotracheal suctioning in mechanically ventilated neonates. Non-pharmacological interventions were compared to no intervention, standard care or another non-pharmacological intervention.

SEARCH METHODS

We conducted searches in June 2023 in the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE via PubMed, Embase, CINAHL and three trial registries. We searched the reference lists of related systematic reviews, and of studies selected for inclusion.

SELECTION CRITERIA

We included randomised controlled trials (RCTs), quasi-RCTs and cluster-RCTs that included term and preterm neonates who were mechanically ventilated via endotracheal tube or via tracheostomy tube and required endotracheal suctioning performed by doctors, nurses, physiotherapists or other healthcare professionals.

DATA COLLECTION AND ANALYSIS

Our main outcome measures were validated composite pain scores (including a combination of behavioural, physiological and contextual indicators). Secondary outcomes included separate physiological and behavioural pain indicators. We used standard methodological procedures expected by Cochrane. For continuous outcome measures, we used a fixed-effect model and reported mean differences (MDs) with 95% confidence intervals (CIs). For categorical outcomes, we reported the typical risk ratio (RR) and risk difference (RD) and 95% CIs. We assessed risk of bias using the Cochrane RoB 1 tool, and assessed the certainty of the evidence using GRADE.

MAIN RESULTS

We included eight RCTs (nine reports), which enroled 386 infants, in our review. Five of the eight studies were included in a meta-analysis. All studies enrolled preterm neonates. Facilitated tucking versus standard care (four studies) Facilitated tucking probably reduces Premature Infant Pain Profile (PIPP) score during endotracheal suctioning (MD -2.76, 95% CI 3.57 to 1.96; I² = 82%; 4 studies, 148 infants; moderate-certainty evidence). Facilitated tucking probably has little or no effect during endotracheal suctioning on: heart rate (MD -3.06 beats per minute (bpm), 95% CI -9.33 to 3.21; I² = 0%; 2 studies, 80 infants; low-certainty evidence); oxygen saturation (MD 0.87, 95% CI -1.33 to 3.08; I² = 0%; 2 studies, 80 infants; low-certainty evidence); or stress and defensive behaviours (SDB) (MD -1.20, 95% CI -3.47 to 1.07; 1 study, 20 infants; low-certainty evidence). Facilitated tucking may result in a slight increase in self-regulatory behaviours (SRB) during endotracheal suctioning (MD 0.90, 95% CI 0.20 to 1.60; 1 study, 20 infants; low-certainty evidence). No studies reported intraventricular haemorrhage (IVH). Familiar odour versus standard care (one study) Familiar odour during endotracheal suctioning probably has little or no effect on: PIPP score (MD -0.30, 95% CI -2.15 to 1.55; 1 study, 40 infants; low-certainty evidence); heart rate (MD -6.30 bpm, 95% CI -16.04 to 3.44; 1 study, 40 infants; low-certainty evidence); or oxygen saturation during endotracheal suctioning (MD -0.80, 95% CI -4.82 to 3.22; 1 study, 40 infants; low-certainty evidence). No studies reported SRB, SDB or IVH. White noise (one study) White noise during endotracheal suctioning probably has little or no effect on PIPP (MD -0.65, 95% CI -2.51 to 1.21; 1 study, 40 infants; low-certainty evidence); heart rate (MD -1.85 bpm, 95% CI -11.46 to 7.76; 1 study, 40 infants; low-certainty evidence); or oxygen saturation (MD 2.25, 95% CI -2.03 to 6.53; 1 study, 40 infants; low-certainty evidence). No studies reported SRB, SDB or IVH.

AUTHORS' CONCLUSIONS

Facilitated tucking / four-handed care / gentle human touch probably reduces PIPP score. The evidence of a single study suggests that facilitated tucking / four-handed care / gentle human touch slightly increases self-regulatory and approach behaviours during endotracheal suctioning. Based on a single study, familiar odour and white noise have little or no effect on any of the outcomes compared to no intervention. The use of expressed breast milk or oral sucrose suggests that there is no discernible advantage of one method over the other for reducing pain during endotracheal suctioning. None of the studies reported on any of the prespecified secondary outcomes of adverse events.

Developing mathematical models to compare and analyse the pharmacokinetics of morphine and fentanyl

Background and Aims

The two-compartment model is generally used in pharmacokinetics to illustrate the distribution and excretion of drugs. In this study, we evaluated the distribution patterns of morphine and fentanyl by using a two-compartment model.

Methods

Using numeric analysis techniques, non-linear ordinary differential equations were used to mathematically analyse drug distribution, transition, and concentration in the body compartments. Math Works, Inc., MATLAB, version 2023a, a programming tool, was used to characterise the impact of initial concentration and rate constants on the kinetics of the drug. For a definite therapeutic concentration of morphine and fentanyl in blood, pharmacokinetic characteristics were plotted.

Results

The study results showed the time taken by morphine and fentanyl to reach a target concentration in the blood that is sufficient to generate the preferred therapeutic effects. The mathematical models comparing morphine and fentanyl pharmacokinetics showed that fentanyl reached the target therapeutic concentration 125 minutes earlier than morphine and was metabolised and removed from the body more rapidly (44 minutes earlier than morphine).

Conclusion

These comparative mathematical models on morphine and fentanyl enable the determination of drug dosages and understanding of drug efficacy that facilitates optimising dosing regimens. The right choice between them can be made based on the time to reach the target therapeutic concentration in the blood, elimination time, severity of pain, and patient characteristics.

Predicting Volume of Distribution in Neonates: Performance of Physiologically Based Pharmacokinetic Modelling

The volume of distribution at steady state (Vss) in neonates is still often estimated through isometric scaling from adult values, disregarding developmental changes beyond body weight. This study aimed to compare the accuracy of two physiologically based pharmacokinetic (PBPK) Vss prediction methods in neonates (Poulin & Theil with Berezhkovskiy correction (P&T+) and Rodgers & Rowland (R&R)) with isometrical scaling. PBPK models were developed for 24 drugs using in-vitro and in-silico data. Simulations were done in Simcyp (V22) using predefined populations. Clinical data from 86 studies in neonates (including preterms) were used for comparison, and accuracy was assessed using (absolute) average fold errors ((A)AFEs). Isometric scaling resulted in underestimated Vss values in neonates (AFE: 0.61), and both PBPK methods reduced the magnitude of underprediction (AFE: 0.82-0.83). The P&T+ method demonstrated superior overall accuracy compared to isometric scaling (AAFE of 1.68 and 1.77, respectively), while the R&R method exhibited lower overall accuracy (AAFE: 2.03). Drug characteristics (LogP and ionization type) and inclusion of preterm neonates did not significantly impact the magnitude of error associated with isometric scaling or PBPK modeling. These results highlight both the limitations and the applicability of PBPK methods for the prediction of Vss in the absence of clinical data.

Ketamine Analgesia as an Alternative to General Anesthesia During Laser Treatment for Retinopathy of Prematurity

PURPOSE

To determine the safety and efficacy of ketamine analgesia as an alternative to general anesthesia during laser treatment for retinopathy of prematurity (ROP).

METHODS

Eighteen premature neonates with ROP underwent laser treatment. The procedure was performed in the operating room, and the neonates were admitted to the neonatal intensive care unit (NICU) after the procedure. An initial dose of 1 mg/kg of ketamine was administered. If the neonate exhibited movement or distress during the procedure, incremental doses of ketamine were administered. Perioperative ventilation status, severity of pain during the procedure, surgeon satisfaction, and perioperative events were recorded.

RESULTS

Eighteen premature neonates underwent ketamine analgesia during laser treatment for ROP. The procedure was performed in 16 patients with good tolerance and without events. The Premature Infant Pain Profile (PIPP) scores during the procedure were 5 or less in 12 neonates (44.4%), 5 to 10 in 4 neonates (22.2%), and greater than 10 in 2 (11.1%) neonates. Three neonates had perioperative events, which resolved completely with minimal intervention. None of the neonates needed intubation perioperatively, and hemodynamic instability, hypotension, and bradycardia were not recorded in any of the neonates during or after the procedure.

CONCLUSIONS

The ROP laser treatment under ketamine sedation could be performed in premature neonates with few perioperative complications and provide satisfactory operative conditions. [J Pediatr Ophthalmol Strabismus. 2022;59(6):416-421.].

Pharmacokinetic modeling and simulation to understand diamorphine dose-response in neonates, children, and adolescents

Pharmacokinetic-pharmacodynamic modeling and simulation can facilitate understanding and prediction of exposure-response relationships in children with acute or chronic pain. The pharmacokinetics of diamorphine (diacetylmorphine, heroin), a strong opioid, remain poorly quantified in children and dose is often guided by clinical acumen. This tutorial demonstrates how a model to describe intranasal and intravenous diamorphine pharmacokinetics can be fashioned from a model for diamorphine disposition in adults and a model describing morphine disposition in children. Allometric scaling and maturation models were applied to clearances and volumes to account for differences in size and age between children and adults. The utility of modeling and simulation to gain insight into the analgesic exposure-response relationship is demonstrated. The model explains reported observations, can be used for interrogation, interpolated to determine equianalgesia and inform future clinical studies. Simulation was used to illustrate how diamorphine is rapidly metabolized to morphine via its active metabolite 6-monoacetylmorphine, which mediates an early dopaminergic response accountable for early euphoria. Morphine formation is then responsible for the slower, prolonged analgesic response. Time-concentration profiles of diamorphine and its metabolites reflected disposition changes with age and were used to describe intravenous and intranasal dosing regimens. These indicated that morphine exposure in children after intranasal diamorphine 0.1 mg.kg-1 was similar to that after intranasal diamorphine 5 mg in adults. A target concentration of morphine 30 μg.L-1 can be achieved by a diamorphine intravenous infusion in neonates 14 μg.kg-1 .h-1 , in a 5-year-old child 42 μg.kg-1 .h-1 and in an 15 year-old-adolescent 33 μg.kg-1 .h-1 .

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.

Model-Informed Bayesian Estimation Improves the Prediction of Morphine Exposure in Neonates and Infants

BACKGROUND

Pain control in infants is an important clinical concern, with potential long-term adverse neurodevelopmental effects. Intravenous morphine is routinely administered for postoperative pain management; however, its dose-concentration-response relationship in neonates and infants has not been well characterized. Although the current literature provides dosing guidelines for the average infant, it fails to control for the large unexplained variability in morphine clearance and response in individual patients. Bayesian estimation can be used to control for some of this variability. The authors aimed to evaluate morphine pharmacokinetics (PKs) and exposure in critically ill neonates and infants receiving standard-of-care morphine therapy and compare a population-based approach to the model-informed Bayesian techniques.

METHODS

The PKs and exposure of morphine and its active metabolites were evaluated in a prospective opportunistic PK study using 221 discarded blood samples from 57 critically ill neonates and infants in the neonatal intensive care unit. Thereafter, a population-based PK model was compared with a Bayesian adaptive control strategy to predict an individual's PK profile and morphine exposure over time.

RESULTS

Among the critically ill neonates and infants, morphine clearance showed substantial variability with a 40-fold range (ie, 2.2 to 87.1, mean 23.7 L/h/70 kg). Compared with the observed morphine concentrations, the population-model based predictions had an R of 0.13, whereas the model-based Bayesian predictions had an R of 0.61.

CONCLUSIONS

Model-informed Bayesian estimation is a better predictor of morphine exposure than PK models alone in critically ill neonates and infants. A large variability was also identified in morphine clearance. A further study is warranted to elucidate the predictive covariates and precision dosing strategies that use morphine concentration and pain scores as feedbacks.

Quantifying the pharmacodynamics of morphine in the treatment of postoperative pain in preverbal children

While the pharmacokinetics of morphine in children have been studied extensively, little is known about the pharmacodynamics of morphine in this population. Here, we quantified the concentration‐effect relationship of morphine for postoperative pain in preverbal children between 0 and 3 years of age. For this, we applied item response theory modeling in the pharmacokinetic/pharmacodynamic analysis of COMFORT‐Behavior (COMFORT‐B) scale data from 2 previous clinical studies. In the model, we identified a sigmoid maximal efficacy model for the effect of morphine and found that in 26% of children, increasing morphine concentrations were not associated with lower pain scores (nonresponders to morphine up‐titration). In responders to morphine up‐titration, the COMFORT‐B score slowly decreases with increasing morphine concentrations at morphine concentrations >20 ng/mL. In nonresponding children, no decrease in COMFORT‐B score is expected. In general, lower baseline COMFORT‐B scores (2.1 points on average) in younger children (postnatal age <10.3 days) were found. Based on the model, we conclude that the percentage of children at a desirable COMFORT‐B score is maximized at a morphine concentration between 5 and 30 ng/mL for children aged <10 days, and between 5 and 40 ng/mL for children >10 days. These findings support a dosing regimen previously suggested by Krekels et al, which would put >95% of patients within this morphine target concentration range at steady state. Our modeling approach provides a promising platform for pharmacodynamic research of analgesics and sedatives in children.

Safety and effectiveness of parent- or nurse-controlled analgesia in neonates: a systematic review

OBJECTIVE

The aim of this systematic review was to determine the safety and effectiveness of parent- or nurse-controlled analgesia on neonatal patient outcomes. More specifically, the objective was to determine the effect of parent- or nurse-controlled analgesia on neonatal pain scores, analgesic use, and incidence of iatrogenic withdrawal syndrome, as well as any opioid-associated adverse events.

INTRODUCTION

Despite recent innovations in neonatology leading to significant improvements in short- and long-term outcomes for newborns requiring intensive care, optimal management of pain and distress remains a challenge for the treating multidisciplinary team. The inability of neonates to communicate pain easily, inconsistent practice among health professionals, insufficient analgesic prescriptions, and delays in medical reviews all impact effective pain management. Exploring the effect of parent- or nurse-controlled analgesia may identify a modality that negates these concerns and improves the pharmacological management of pain in newborns.

INCLUSION CRITERIA

This review considered experimental and observational studies evaluating the safety and effectiveness of parent- or nurse-controlled analgesia that included babies born at 23 weeks' gestation to four weeks post-term. The interventions considered for inclusion were any type of analgesia delivered by an infusion pump that allowed bolus dosing or a continuous analgesic infusion with bolus dosing as required. Studies using algorithms and protocols to guide timing and dosage were eligible for inclusion. Comparators included the standard management of pain for neonates in the newborn intensive care unit. A modification to the a priori protocol was made to include all neonates nursed outside of a neonatal intensive care unit to ensure all studies that examined the use of parent- or nurse-controlled analgesia in the neonatal population were included in the review.

METHODS

An extensive search of six major databases was conducted (CINAHL, Cochrane Library, Embase, PubMed, PsycINFO, and Web of Science). Studies published from 1997 to 2020 in English were considered for inclusion in this review. Databases searched for unpublished studies included MedNar and ProQuest Dissertations and Theses.

RESULTS

Fourteen studies were included in this review: two randomized controlled trials, six quasi-experimental studies, one case-control study, and five case series. There was considerable heterogeneity in the interventions and study outcome measures within the studies, resulting in an inability to statistically pool results. The small sample sizes and inability to distinguish data specific to neonates in six of the studies resulted in low quality of evidence for the safety and effectiveness of parent- or nurse-controlled analgesia in neonates. However, studies reporting neonatal data demonstrated low pain scores and a trend in reduced opioid consumption when parent- or nurse-controlled analgesia was used.

CONCLUSIONS

The use of parent- or nurse-controlled analgesia in the neonatal population has shown some effect in reducing the amount of opioid analgesia required without compromising pain relief or increasing the risk of adverse events. Due to the paucity of evidence available, certainty of the results is compromised; therefore, larger trials exploring the use of parent- or nurse-controlled analgesia in neonates and the development of nurse-led models for analgesia delivery are needed.

SYSTEMATIC REVIEW REGISTRATION NUMBER

PROSPERO CRD42018114382.

Preterm Physiologically Based Pharmacokinetic Model. Part II: Applications of the Model to Predict Drug Pharmacokinetics in the Preterm Population

BACKGROUND

Preterm neonates are usually not part of a traditional drug development programme, however they are frequently administered medicines. Developing modelling and simulation tools, such as physiologically based pharmacokinetic (PBPK) models that incorporate developmental physiology and maturation of drug metabolism, can be used to predict drug exposure in this group of patients, and may help to optimize drug dose adjustment.

OBJECTIVE

The aim of this study was to assess and verify the predictability of a preterm PBPK model using compounds that undergo diverse renal and/or hepatic clearance based on the knowledge of their disposition in adults.

METHODS

A PBPK model was developed in the Simcyp Simulator V17 to predict the pharmacokinetics (PK) of drugs in preterm neonates. Drug parameters for alfentanil, midazolam, caffeine, ibuprofen, gentamicin and vancomycin were collated from the literature. Predicted PK parameters and profiles were compared against the observed data.

RESULTS

The preterm PBPK model predicted the PK changes of the six compounds using ontogeny functions for cytochrome P450 (CYP) 1A2, CYP2C9 and CYP3A4 after oral and intravenous administrations. For gentamicin and vancomycin, the maturation of renal function was able to predict the exposure of these two compounds after intravenous administration. All PK parameter predictions were within a twofold error criteria.

CONCLUSION

While the developed preterm model for the prediction of PK behaviour in preterm patients is not intended to replace clinical studies, it can potentially help with deciding on first-time dosing in this population and study design in the absence of clinical data.

Opioids for newborn infants receiving mechanical ventilation

BACKGROUND

Mechanical ventilation is a potentially painful and discomforting intervention that is widely used in neonatal intensive care. Newborn infants demonstrate increased sensitivity to pain, which may affect clinical and neurodevelopmental outcomes. The use of drugs that reduce pain might be important in improving survival and neurodevelopmental outcomes.

OBJECTIVES

To determine the benefits and harms of opioid analgesics for neonates (term or preterm) receiving mechanical ventilation compared to placebo or no drug, other opioids, or other analgesics or sedatives.

SEARCH METHODS

We used the standard search strategy of Cochrane Neonatal to search the Cochrane Central Register of Controlled Trials (CENTRAL; 2020, Issue 9), in the Cochrane Library; MEDLINE via PubMed (1966 to 29 September 2020); Embase (1980 to 29 September 2020); and the Cumulative Index to Nursing and Allied Health Literature (CINAHL) (1982 to 29 September 2020). We searched clinical trials databases, conference proceedings, and the reference lists of retrieved articles for randomised controlled trials and quasi-randomised trials.

SELECTION CRITERIA

We included randomised and quasi-randomised controlled trials comparing opioids to placebo or no drug, to other opioids, or to other analgesics or sedatives in newborn infants on mechanical ventilation. We excluded cross-over trials. We included term (≥ 37 weeks' gestational age) and preterm (< 37 weeks' gestational age) newborn infants on mechanical ventilation. We included any duration of drug treatment and any dosage given continuously or as bolus; we excluded studies that gave opioids to ventilated infants for procedures.

DATA COLLECTION AND ANALYSIS

For each of the included trials, we independently extracted data (e.g. number of participants, birth weight, gestational age, types of opioids) using Cochrane Effective Practice and Organisation of Care Group (EPOC) criteria and assessed the risk of bias (e.g. adequacy of randomisation, blinding, completeness of follow-up). We evaluated treatment effects using a fixed-effect model with risk ratio (RR) for categorical data and mean difference (MD) for continuous data. We used the GRADE approach to assess the certainty of evidence.

MAIN RESULTS

We included 23 studies (enrolling 2023 infants) published between 1992 and 2019. Fifteen studies (1632 infants) compared the use of morphine or fentanyl versus placebo or no intervention. Four studies included both term and preterm infants, and one study only term infants; all other studies included only preterm infants, with five studies including only very preterm infants. We are uncertain whether opioids have an effect on the Premature Infant Pain Profile (PIPP) Scale in the first 12 hours after infusion (MD -5.74, 95% confidence interval (CI) -6.88 to -4.59; 50 participants, 2 studies) and between 12 and 48 hours after infusion (MD -0.98, 95% CI -1.35 to -0.61; 963 participants, 3 studies) because of limitations in study design, high heterogeneity (inconsistency), and imprecision of estimates (very low-certainty evidence - GRADE). The use of morphine or fentanyl probably has little or no effect in reducing duration of mechanical ventilation (MD 0.23 days, 95% CI -0.38 to 0.83; 1259 participants, 7 studies; moderate-certainty evidence because of unclear risk of bias in most studies) and neonatal mortality (RR 1.12, 95% CI 0.80 to 1.55; 1189 participants, 5 studies; moderate-certainty evidence because of imprecision of estimates). We are uncertain whether opioids have an effect on neurodevelopmental outcomes at 18 to 24 months (RR 2.00, 95% CI 0.39 to 10.29; 78 participants, 1 study; very low-certainty evidence because of serious imprecision of the estimates and indirectness). Limited data were available for the other comparisons (i.e. two studies (54 infants) on morphine versus midazolam, three (222 infants) on morphine versus fentanyl, and one each on morphine versus diamorphine (88 infants), morphine versus remifentanil (20 infants), fentanyl versus sufentanil (20 infants), and fentanyl versus remifentanil (24 infants)). For these comparisons, no meta-analysis was conducted because outcomes were reported by one study.

AUTHORS' CONCLUSIONS

We are uncertain whether opioids have an effect on pain and neurodevelopmental outcomes at 18 to 24 months; the use of morphine or fentanyl probably has little or no effect in reducing the duration of mechanical ventilation and neonatal mortality. Data on the other comparisons planned in this review (opioids versus analgesics; opioids versus other opioids) are extremely limited and do not allow any conclusions. In the absence of firm evidence to support a routine policy, opioids should be used selectively - based on clinical judgement and evaluation of pain indicators - although pain measurement in newborns has limitations.

Opioid Treatment for Neonatal Opioid Withdrawal Syndrome: Current Challenges and Future Approaches

Chronic intrauterine exposure to psychoactive drugs often results in neonatal opioid withdrawal syndrome (NOWS). When nonpharmacologic measures are insufficient in controlling NOWS, morphine, methadone, and buprenorphine are first-line medications commonly used to treat infants with NOWS because of in utero exposure to opioids. Research suggests that buprenorphine may be the leading drug therapy used to treat NOWS when compared with morphine and methadone. Currently, there are no consensus or standardized treatment guidelines for medications prescribed for NOWS. Opioids used to treat NOWS exhibit large interpatient variability in pharmacokinetics (PK) and pharmacodynamic (PD) response in neonates. Organ systems undergo rapid maturation after birth that may alter drug disposition and exposure for any given dose during development. Data regarding the PK and PD of opioids in neonates are sparse. Pharmacometric methods such as physiologically based pharmacokinetic and population pharmacokinetic modeling can be used to explore factors predictive of some of the variability associated with the PK/PD of opioids in newborns. This review discusses the utility of pharmacometric techniques for enhancing precision dosing in infants requiring opioid treatment for NOWS. Applying these approaches may contribute to optimizing the outcome by reducing cumulative drug exposure, mitigating adverse drug effects, and reducing the burden of NOWS in neonates.

Identifying the Neurodevelopmental Differences of Opioid Withdrawal

Stopping opioid medications can result in a debilitating withdrawal syndrome in chronic users. Opioid withdrawal can occur at all ages, but mechanistic understanding of this condition is predominantly derived from adult studies. Here, we examined whether there are age-dependent differences in the behavioural phenotype and cellular indices of opioid withdrawal. We tested this by assessing the behavioural and cFos response (a surrogate marker for neuronal activation) to morphine withdrawal in C57BL/6J mice across key developmental stages-neonatal, adolescent, and adulthood. Mice in all age groups received escalating doses of morphine (10-50 mg/kg) over 5 days and withdrawal was precipitated by a single injection of the opioid receptor antagonist naloxone (2 mg/kg) two hours after the last morphine dose. In adult and adolescent mice, withdrawal behaviours were robust, with age-related differences in autonomic and somatic signs. In both groups, cFos expression was increased in spinally projecting neurons within the Periaqueductal Grey (PAG), Rostro-ventromedial Medulla (RVM), and Locus Coeruleus. Neonatal animals displayed both a distinct behavioural withdrawal and cFos expression profile. Notably, in young animals cFos expression was increased within the PAG and LC, but decreased in the RVM. In summary, naloxone challenge precipitated robust opioid withdrawal behaviours across all developmental stages with neonatal animals displaying differences in withdrawal behaviours and unique neuronal activation patterns within key brainstem regions.

The Influence of Haemostatic System Maturation on the Dose-Response Relationship of Unfractionated Heparin

BACKGROUND

Unfractionated heparin (UFH) dosing and monitoring guidelines for children are often extrapolated from adult data. This practice is suboptimal given the inherent differences in haemostatic maturation and drug handling in children compared with adults.

OBJECTIVE

The aim of this work was to investigate the impact of haemostatic system maturation on the dose-response relationship of UFH in children.

METHODS

A quantitative model for haemostasis in adults was adapted to account for maturation in UFH pharmacokinetic (PK) parameters with and without age-related changes in coagulation factor concentrations. The adult and adapted models were used to predict the time courses of anti-factor Xa activity (aXa) and activated partial thromboplastin time (aPTT) in patients receiving UFH infusion. Predictions from both models were compared with observed aXa and aPTT measurements from 31 paediatric patients receiving UFH during extracorporeal membrane oxygenation (ECMO).

RESULTS

The model with maturation for both UFH PK and the haemostatic system had an improved aXa and aPTT predictive performance compared with maturation in UFH PK only and the original adult model. Despite the minor effect of haemostatic system maturation on baseline aPTT, it led to substantial changes in the time course of aPTT sensitivity to UFH. This finding suggests that between-subject variability in clotting factors concentrations is potentially a major contributor to the overall variability of aPTT response to UFH. In addition, time-varying clotting factors concentrations may explain within-subject changes in aPTT sensitivity to UFH.

CONCLUSION

We developed the first quantitative systems pharmacology (QSP) model that provides a mechanistic and quantitative basis for linking physiological and pharmacological maturation to UFH effect and response biomarkers. After appropriate clinical validation, the model could be useful for the development of paediatric-specific individualised UFH dosing recommendations.

Pharmacotherapy of neonatal opioid withdrawal syndrome: a review of pharmacokinetics and pharmacodynamics

INTRODUCTION

Neonatal opioid withdrawal syndrome (NOWS) often arises in infants born to mothers who used opioids during pregnancy. Morphine, methadone, and buprenorphine are the most common first-line treatments, whereas clonidine and phenobarbital are generally reserved for adjunctive therapy. These drugs exhibit substantial pharmacokinetic (PK) and pharmacodynamic (PD) variability. Current pharmacological treatments for NOWS are based on institutional protocols and largely rely on empirical treatment of patient symptoms.

AREAS COVERED

This article reviews the PK/PD of NOWS pharmacotherapies with a focus on the implication of physiological development and maturation. Body size-standardized clearance is consistently low in neonates, except for methadone. This can be ascribed to underdeveloped metabolic and elimination pathways. The effects of pharmacogenetics have been clarified especially for morphine. The PK/PD relationship of medications used in the treatment of NOWS is generally understudied.

EXPERT OPINION

Providing an appropriate opioid dose in neonates is challenging. Advancements in quantitative pharmacology and PK/PD modeling approaches facilitate identification of key factors driving PK/PD variability and characterization of exposure-response relationships. PK/PD model-informed simulations have been widely employed to define age-appropriate pediatric dosing regimens. The model-informed approach holds promise to aid more rational use of medications in the treatment of NOWS.

Extrapolation of Drug Clearance in Children ≤ 2 Years of Age from Empirical Models Using Data from Children (> 2 Years) and Adults

BACKGROUND

The application of modeling and simulation approaches in clinical pharmacology studies has gained momentum over the last 20 years.

OBJECTIVES

The objective of this study was to develop six empirical models from clearance data obtained from children aged > 2 years and adults to evaluate the suitability of the models to predict drug clearance in children aged ≤ 2 years (preterm, term, and infants).

METHODS

Ten drugs were included in this study and administered intravenously: alfentanil, amikacin, busulfan, cefetamet, meperidine, oxycodone, propofol, sufentanil, theophylline, and tobramycin. These drugs were selected according to the availability of individual subjects' weight, age, and clearance data (concentration-time data for these drugs were not available to the author). The chosen drugs are eliminated by extensive metabolism by either the renal route or both the renal and hepatic routes. The six empirical models were (1) age and body weight-dependent sigmoidal maximum possible effect (E_max) maturation model, (2) body weight-dependent sigmoidal E_max model, (3) uridine 5'-diphospho [body weight-dependent allometric exponent model (BDE)], (4) age-dependent allometric exponent model (ADE), (5) a semi-physiological model, and (6) an allometric model developed from children aged > 2 years to adults. The model-predicted clearance values were compared with observed clearance values in an individual child. In this analysis, a prediction error of ≤ 50% for mean or individual clearance values was considered acceptable.

RESULTS

Across all age groups and the ten drugs, data for 282 children were compared between observed and model-predicted clearance values. The validation data consisted of 33 observations (sum of different age groups for ten drugs). Only three of the six models (body weight-dependent sigmoidal E_max model, ADE, and semi-physiological model) provided reasonably accurate predictions of clearance (> 80% observation with ≤ 50% prediction error) in children aged ≤ 2 years. In most instances, individual predicted clearance values were erratic (as indicated by % error) and were not in agreement with the observed clearance values.

CONCLUSIONS

The study indicated that simple empirical models can provide more accurate results than complex empirical models.

Is Intensive Care Unit Admission Necessary After Removal of Mandibular Distraction Devices in Infants With Robin Sequence?

OBJECTIVE

Intensive care unit (ICU) care is routinely required after the operation to initiate mandibular distraction osteogenesis (MDO) in infants with Robin sequence (RS). Many patients are also managed in the ICU after subsequent device removal. It is uncertain if ICU care, which is expensive and limited, is necessary after this second operation. The objective of this study was to evaluate the incidence of respiratory events following device removal. We hypothesized that respiratory events would be infrequent and non-ICU inpatient monitoring would be adequate.

DESIGN

This is a retrospective study of patients with RS from 2013 to 2018.

PATIENTS

Patients were included if they had MDO and distractor removal during the first year of life. Patients were excluded if they had a tracheostomy or remained intubated after distractor removal.

MAIN OUTCOME MEASURE

Postoperative respiratory events.

RESULTS

Twenty-five (60% male) patients were included. Mean age and weight at distractor removal were 142 ± 79 days of life and 5.5 ± 1.1 kg. Mean apnea-hypopnea index after completion of distraction was 1.1 ± 1.5 events/hour. Two (8%) patients experienced postoperative respiratory events that required intervention. In 1 (4% of sample) of these, the event was deemed to have benefited from ICU-level care. Two variables were significantly associated with these events: congenital heart disease (P = .020) and concomitant procedure performed during the same operation (P = .020).

CONCLUSIONS

Intensive care unit-level care is rarely needed after distractor removal in infants with RS. Intensive care unit admission should be considered in patients with congenital cardiac disease and when having multiple operations during the same anesthetic.

Retrospective study of short-term complications associated with early morphine use in intubated premature infants

Relieving neonatal pain is essential for the management of premature infants. Morphine is the most frequently used analgesic in neonatal intensive care. Here we report the relationship between early morphine infusion and the composite outcome of intraventricular hemorrhage and/or death in intubated premature infants. Infants (gestational age ≤ 32 weeks and birth weight < 1,500 g) intubated on admission were retrospectively evaluated in a large tertiary neonatal intensive care unit. Modified log-Poisson regression with robust variance estimator and Cox regression was applied to adjust the relative risk for infants’ outcomes. Of 420 premature infants, 230 (54.7%) received continuous morphine infusion in the first 72 h. Of these, 153 were < 28 gestational weeks; of the 190 patients who did not receive morphine, 63 were < 28 gestational weeks. The analysis revealed that infants < 28 gestational weeks who received morphine were significantly associated with an increased risk for IVH and/or death [adjusted relative risk (aRR) 1.37, 95% confidence interval (CI) 1.1–1.71)], and mortality (aRR 1.83, 95% CI 1.17–2.89). Moreover, in infants < 28 gestational weeks, survival was low in those infants who were exposed to morphine infusion in the first 72 h (hazard ratio 2.11; 95% CI 1.19–3.73). Early morphine infusion is associated with an increased risk for IVH and/or death; however, further studies are required to verify our findings.

Clinical implementation of pharmacogenetics and model-informed precision dosing to improve patient care

Providing maximal therapeutic efficacy without toxicity is a universal goal of rational drug therapy. However, substantial between-patient variability in drug response often impedes such successful treatments and brings the necessity of tailoring drug dose to individual needs for more precise therapy. In many cases plenty of patient characteristics, such as body size, genetic makeup and environmental factors, need to be taken into consideration to find the optimal dose in clinical practice. A pharmacokinetics and pharmacodynamics (PK/PD) model-informed approach offers integration of various patient information to provide an expectation of drug response and derive practical dose estimates to support clinicians' dosing decisions. Such an approach was pioneered in the late 1970s, but its broad clinical acceptance and implementation have been hampered by the lack of widespread computer technology, including user-friendly software tools. This has significantly changed in recent years. With the advent of electronic health records (EHRs) and the ubiquity of user-friendly software tools, we now experience a convergence of clinical information, pharmacogenetics, systems pharmacology and pharmacometrics, and technology. Advanced pharmacometrics research is now more appliable and implementable to improve health care. This article presents examples of successful development and implementation of pharmacogenetics-guided and PK/PD model-informed decision support to facilitate precision dosing, including the development of an EHR-embedded decision support tool. Through the integration of clinical decision support tools in EHRs, clinical pharmacometrics support can be brought directly to the clinical team and the bedside.

The Ontogeny of UDP-glucuronosyltransferase Enzymes, Recommendations for Future Profiling Studies and Application Through Physiologically Based Pharmacokinetic Modelling

Limited understanding of drug pharmacokinetics in children is one of the major challenges in paediatric drug development. This is most critical in neonates and infants owing to rapid changes in physiological functions, especially in the activity of drug-metabolising enzymes. Paediatric physiologically based pharmacokinetic models that integrate ontogeny functions for cytochrome P450 enzymes have aided our understanding of drug exposure in children, including those under the age of 2 years. Paediatric physiologically based pharmacokinetic models have consequently been recognised by the European Medicines Agency and the US Food and Drug Administration as innovative tools in paediatric drug development and regulatory decision making. However, little is currently known about age-related changes in UDP-glucuronosyltransferase-mediated metabolism, which represents the most important conjugation reaction for xenobiotics. Therefore, the objective of the review was to conduct a thorough literature survey to summarise our current understanding of age-related changes in UDP-glucuronosyltransferases as well as associated clinical and experimental sources of variance. Our findings indicate that there are distinct differences in UDP-glucuronosyltransferase expression and activity between isoforms for different age groups. In addition, there is substantial variability between individuals and laboratories reported for human liver microsomes, which results in part from a lack of standardised experimental conditions. Therefore, we provide a number of best practice recommendations for experimental conditions, which ultimately may help improve the quality of data used for quantitative clinical pharmacology approaches, and thus for safe and effective pharmacotherapy in children.

Pharmacokinetic and pharmacodynamic considerations of general anesthesia in pediatric subjects

Introduction: The target concentration strategy uses PKPD information for dose determination. Models have also quantified exposure-response relationships, improved understanding of developmental pharmacokinetics, rationalized dose prescription, provided insight into the importance of covariate information, explained drug interactions and driven decision-making and learning during drug development.Areas covered: The prime PKPD consideration is parameter estimation and quantification of variability. The main sources of variability in children are age (maturation) and weight (size). Model use is mostly confined to pharmacokinetics, partly because anesthesia effect models in the young are imprecise. Exploration of PK and PD covariates and their variability hold potential to better individualize treatment.Expert opinion: The ability to model drugs using computer-based technology is hindered because covariate data required to individualize treatment using these programs remain lacking. Target concentration intervention strategies remain incomplete because covariate information that might better predict individualization of dose is absent. Pharmacogenomics appear a valuable area for investigation for pharmacodynamics and pharmacodynamics. Effect measures in the very young are imprecise. Assessment of the analgesic component of anesthesia is crude. While neuromuscular monitoring is satisfactory, depth of anaesthesia EEG interpretation is inadequate. Closed loop anesthesia is possible with better understanding of EEG changes.

Opioids: A Review of Pharmacokinetics and Pharmacodynamics in Neonates, Infants, and Children

Pain management in the pediatric population is complex for many reasons. Mild pain is usually managed quite well with oral acetaminophen or ibuprofen. Situations involving more severe pain often require the use of an opioid, which may be administered by many different routes, depending on clinical necessity. Acute and chronic disease states, as well as the constantly changing maturational process, produce unique challenges at every level of pediatrics in dosing and management of all medications, especially with regard to high-risk opioids. Although there has been significant progress in the understanding of opioid pharmacokinetics and pharmacodynamics in neonates, infants, children, and adolescents, somewhat limited data exist from which necessary information, concerning the safe and effective use of these agents, may be drawn. The evidence here provided is intended to be helpful in directing the practitioner to patient-specific reasons for preferring one opioid over another. As our knowledge of opioids and their effects has grown, it has become clear that older medications like codeine and meperidine (pethidine) have very limited use in pediatrics. This review provides pharmacokinetic and pharmacodynamic evidence on the currently available opioids: morphine, fentanyl (and derivatives), codeine, meperidine, oxycodone, hydrocodone, hydromorphone, methadone, buprenorphine, butorphanol, nalbuphine, pentazocin, ketobemidone, tramadol, piritramide, naloxone and naltrexone. Morphine, being the most studied opioid analgesic, is the standard against which all others are compared. Pharmacokinetic parameters of morphine that have been found in neonates, i.e., higher volume of distribution, immature metabolic processes that develop at various rates, elimination that is variable based on age and weight, as well as treated and untreated disease processes, are an example of all opioids in the population discussed in this review. Outside the premature and neonatal population, the use of opioids in infants, children, and adolescents quickly begins to resemble the established values found in adults. As such, the concerns (risks) of these medications become comparable to those seen in adults.

A Critical Review on the Relevance of Paracetamol for Procedural Pain Management in Neonates

Effective and safe pain relief in neonates matters. This is not only because of ethical constraints or human empathy, but even more because pain treatment is an important and crucial part of contemporary medical, paramedical, and nursing care to improve the outcome in neonatal intensive care graduates. Paracetamol (acetaminophen) is likely one of the pharmacological tools to attain this, with data on prescription practices suggesting that paracetamol is somehow the "rising star" in neonatal pain management. Besides very rare topical clinical scenarios like peripartal asphyxia and subsequent whole body hypothermia or the use of cardiorespiratory support devices, data on paracetamol pharmacokinetics and metabolism were reported throughout neonatal age or weight ranges, and we have summarized these data. In this review, we subsequently aimed to provide the reader with the currently available observations on the use of paracetamol as analgesic for different pain syndromes (major surgery, minor surgery or trauma, and procedural pain), with focus on the limitations of paracetamol when prescribed for neonatal procedural pain management. We hereby intentionally will not discuss other indications (patent ductus arteriosus and fever) for paracetamol administration in neonates. Based on the available evidence, paracetamol has opioid-sparing effects for major pain syndromes, is effective to treat minor to moderate pain syndromes, but fails for effective procedural pain management in neonates. This efficacy failure for procedural pain management should stimulate us to continue to search for more effective interventions, including non-pharmacological interventions and preventive strategies. Furthermore, there are also upcoming association type of epidemiological studies on the relation between exposure to analgesics-including paracetamol-and the negative short- or long-term outcome characteristics (neuro-behavioral, atopy, and fertility). Consequently and in addition to the search for effective alternatives to prevent or treat pain, studies on long-term outcome following paracetamol exposure are needed to inform all stakeholders on the full effect-side effect balance of the different strategies to treat pain.

Electronic Health Record-Embedded Decision Support Platform for Morphine Precision Dosing in Neonates

Morphine is the opioid most commonly used for neonatal pain management. In intravenous form, it is administered as continuous infusions and intermittent injections, mostly based on empirically established protocols. Inadequate pain control in neonates can cause long-term adverse consequences; however, providing appropriate individualized morphine dosing is particularly challenging due to the interplay of rapid natural physiological changes and multiple life-sustaining procedures in patients who cannot describe their symptoms. At most institutions, morphine dosing in neonates is largely carried out as an iterative process using a wide range of starting doses and then titrating to effect based on clinical response and side effects using pain scores and levels of sedation. Our background data show that neonates exhibit large variability in morphine clearance resulting in a wide range of exposures, which are poorly predicted by dose alone. Here, we describe the development and implementation of an electronic health record-integrated, model-informed decision support platform for the precision dosing of morphine in the management of neonatal pain. The platform supports pharmacokinetic model-informed dosing guidance and has functionality to incorporate real-time drug concentration information. The feedback is inserted directly into prescribers' workflows so that they can make data-informed decisions. The expected outcomes are better clinical efficacy and safety with fewer side effects in the neonatal population.

Continuous intravenous to oral morphine switch in very premature ventilated infants: A retrospective study on efficacy, efficiency, and tolerability

Background

Continuous intravenous (IV) morphine is commonly used in ventilated neonates. Oral route is theoretically feasible but data on oral morphine in ventilated premature infants are lacking.

Objective

To assess the efficacy, efficiency, and tolerability of a continuous intravenous to oral morphine switch protocol.

Design

Retrospective study.

Setting

Single level III center's neonatal intensive care unit.

Patients

Ventilated premature infants hospitalized in the NICU in 2016 and 2017, receiving continuous IV morphine with an expected ventilation course of at least 72 more hours. We excluded patients treated for withdrawal syndrome or palliative care.

Interventions

Continuous IV to oral morphine switch with the same initial cumulated daily dose.

Main outcome measures

Pain scores (ComfortNeo scale) and morphine doses were analyzed over time using Friedman's test in the 24 hours preceding and the 48 hours following the oral switch. Adverse effects attributable to opioids were collected.

Results

Seventeen infants were included with a median [IQR] gestational age at birth of 25.9 [24.6‐26.9] weeks and a median postnatal age at oral switch of 30 [22‐36] days. One patient's intravenous treatment had to be resumed because of a high ComfortNeo score. All others remained on oral morphine. No significant change over time was observed for ComfortNeo scores (P = .15). Median [IQR] doses were 13.5 [10‐20] µg/kg/h in the IV period and significantly increased to 15 [10‐25] µg/kg/h in the oral period (P = .009). No short‐term respiratory, digestive, or urinary adverse event was observed. After a median [IQR] duration of 13 [4‐20] days of oral morphine treatment, 11 (65%) patients showed signs of withdrawal. Upon hospital discharge, 16 infants (94%) had bronchopulmonary dysplasia and none had severe cerebral abnormality on brain imaging.

Conclusion

Oral morphine might be useful in ventilated neonates in the NICU but deserves further studies and additional safety assessment.

Analgesics and Sedatives in Critically Ill Newborns and Infants: The Impact on Long-Term Neurodevelopment

Inadequate pain and/or stress management in preterm- and term-born infants has been associated with increased morbidity and even mortality. However, exposure to analgosedatives during early infancy may also be one of the risk factors for subsequent neurodevelopmental impairment, at least in animal studies. Because infants admitted to neonatal or pediatric intensive care units may receive high amounts of these drugs for prolonged periods of time and the majority of these infants nowadays survive to discharge, this is of major concern. A balanced approach that incorporates the assessment and quantification of both wanted effects as well as unwanted side effects is therefore needed. In this article, the optimal dose determination of commonly used analgosedative drugs as well as their potential long-term effects on the developing human brain and neuropsychological functioning are reviewed.

Pharmacokinetics of morphine in encephalopathic neonates treated with therapeutic hypothermia

OBJECTIVE

Morphine is a commonly used drug in encephalopathic neonates treated with therapeutic hypothermia after perinatal asphyxia. Pharmacokinetics and optimal dosing of morphine in this population are largely unknown. The objective of this study was to describe pharmacokinetics of morphine and its metabolites morphine-3-glucuronide and morphine-6-glucuronide in encephalopathic neonates treated with therapeutic hypothermia and to develop pharmacokinetics based dosing guidelines for this population.

STUDY DESIGN

Term and near-term encephalopathic neonates treated with therapeutic hypothermia and receiving morphine were included in two multicenter cohort studies between 2008-2010 (SHIVER) and 2010-2014 (PharmaCool). Data were collected during hypothermia and rewarming, including blood samples for quantification of morphine and its metabolites. Parental informed consent was obtained for all participants.

RESULTS

244 patients (GA mean (sd) 39.8 (1.6) weeks, BW mean (sd) 3,428 (613) g, male 61.5%) were included. Morphine clearance was reduced under hypothermia (33.5°C) by 6.89%/°C (95% CI 5.37%/°C- 8.41%/°C, p<0.001) and metabolite clearance by 4.91%/°C (95% CI 3.53%/°C- 6.22%/°C, p<0.001) compared to normothermia (36.5°C). Simulations showed that a loading dose of 50 μg/kg followed by continuous infusion of 5 μg/kg/h resulted in morphine plasma concentrations in the desired range (between 10 and 40 μg/L) during hypothermia.

CONCLUSIONS

Clearance of morphine and its metabolites in neonates is affected by therapeutic hypothermia. The regimen suggested by the simulations will be sufficient in the majority of patients. However, due to the large interpatient variability a higher dose might be necessary in individual patients to achieve the desired effect.

TRIAL REGISTRATION

www.trialregister.nl NTR2529.

Influence of OCT1 Ontogeny and Genetic Variation on Morphine Disposition in Critically Ill Neonates: Lessons From PBPK Modeling and Clinical Study

Morphine is commonly used for analgesia in the neonatal intensive care unit (NICU) despite having highly variable pharmacokinetics (PKs) between individual patients. The pharmacogenetic (PG) effect of variants at the loci of organic cation transporter 1 (OCT1) and UDP-glucuronosyltransferase 2B7 (UGT2B7) on age-dependent morphine clearance were evaluated in a cohort of critically ill neonatal patients using an opportunistic sampling design. Our primary results demonstrate the significant influence of OCT1 genotype (P < 0.05) and gestational age (P ≤ 0.005) on morphine PKs. A physiologically based pharmacokinetic (PBPK) model for morphine that accounted for OCT1 ontogeny and PG effect in post-term neonates adequately described the clinically observed variability in morphine PKs. This study serves as a proof of concept for genotype-dependent drug transporter ontogeny in neonates.

Negligible impact of birth on renal function and drug metabolism

BACKGROUND

Transition from the intrauterine to the extrauterine environment in neonates is associated with major changes in blood flow and oxygenation with consequent increases in metabolic functions. The additional impact of birth on renal function and drug metabolism above that predicted by postmenstrual age and allometry is uncertain. Increased clearance at birth could reduce analgesic effect attributable to a lowering of plasma concentration. These elimination processes can be described using the clearance concept.

METHODS

Data from four publications that investigated the time course of glomerular filtration rate and clearance of paracetamol, morphine and tramadol were reanalyzed. The effect of birth, based on postnatal age, was used in conjunction with a theory-based allometric size scaling and maturation based on postmenstrual age.

RESULTS

Postnatal age had a short-term effect on the time course of clearance distinguishable from the well-known slower maturation based on postmenstrual age. While elimination might be relatively reduced by 15%-45% at birth, there is a rapid increase in elimination for 1-3 weeks after birth to be 15% greater than that predicted by postmenstrual age alone.

CONCLUSION

Birth is associated with a small increase in clearance in addition to that described by postmenstrual age for common analgesic drugs cleared by glucuronide conjugation (morphine, paracetamol) or by the P450 cytochrome oxidase (tramadol) and renal systems. While the increase is of biological interest, it would not be expected to have any clinically relevant impact on renal function or drug dosing. The processes of maturation described by these models are potentially applicable to any drug elimination process.

Misconceptions and issues regarding allometric scaling during the drug development process

INTRODUCTION

Allometry is the study of size and its consequences. The simple hypothesis of allometric scaling is that all physiological parameters are proportional to body size or body mass. This review examines the development of theory-based allometry or fixed exponents (0.75 and 1.0 for basal metabolic rate and volume, respectively) and the evidence for or against the theory. The main focus of this report is to show the readers that there is enough evidence from experimental data that negate the concept of theory-based allometry in biology, physiology, and pharmacokinetics. Areas covered: In this review, the history of the development of theoretical allometry and the strong evidence against theory-based allometry demonstrated by experimental data is provided. During drug development, allometry is applied to both inter-species (from animals to humans) and intra-species (adults to children) scaling. These two forms of allometric scaling in the context of theory-based allometry are discussed and provide insight on scientific progress that refute theory-based allometry. Expert opinion: Theory-based allometry is a mere theory and experimental data and real-life observations strongly negate the existence of such a theory. Pharmacostatistical and physiological models based on theory-based allometry can be misleading and incorrect because the theory-based allometric exponent 0.75 is not universal. The exponents of allometry are data dependent and are not fixed in the universe.

Population pharmacokinetics of valproic acid in epileptic children: Effects of clinical and genetic factors

Valproic acid (VPA) is a first-line anti-epileptic drug that is used in the treatment of generalized and partial seizures. Gene variants had been proved to influence the pharmacokinetics (PK) of VPA and contribute to its inter-individual variability (IIV). The aim of this study was to systematically investigate the effects of candidate gene variants (CYPs, UGTs, ABC transporters, and nuclear receptors) on VPA PK in Chinese children with epilepsy. A total of 1065 VPA serum trough concentrations at steady state were collected from 264 epileptic pediatric patients aged 3 months to 16 years. The population pharmacokinetic (PPK) model was developed using a nonlinear mixed effects modelling (NONMEM) approach. For the final PPK model, the oral clearance (CL/F) of VPA was estimated to be 0.259 L/h with IIV of 13.3%. The estimates generated by NONMEM indicated that the VPA CL/F was significantly influenced by patient body weight (increased by an exponent of 0.662), co-administration with carbamazepine (increased CL/F by 22%), and daily dose of VPA (increased by an exponent of 0.22). CL/F in patients with the LEPR rs1137101 variant (668 AG and GG genotypes) was much lower than in patients with the AA genotype (17.8% and 22.6% lower, respectively). However, none of the CYPs or UGTs gene variants was found to influence the PK of VPA in this study. Evaluation by bootstrap and normalized prediction distribution error (NPDE) showed that the final model was stable. The predictive performance was evaluated by goodness-of-fit (GOF) plots and visual predictive checks (VPC), and the results indicated satisfactory precision. Our model suggests a correlation between VPA CL/F and LEPR rs1137101 variants, which might be beneficial in the context of individual dose optimization.

PBPK Model of Morphine Incorporating Developmental Changes in Hepatic OCT1 and UGT2B7 Proteins to Explain the Variability in Clearances in Neonates and Small Infants

Morphine has large pharmacokinetic variability, which is further complicated by developmental changes in neonates and small infants. The impacts of organic cation transporter 1 (OCT1) genotype and changes in blood-flow on morphine clearance (CL) were previously demonstrated in children, whereas changes in UDP-glucuronosyltransferase 2B7 (UGT2B7) activity showed a small effect. This study, targeting neonates and small infants, was designed to assess the influence of developmental changes in OCT1 and UGT2B7 protein expression and modified blood-flow on morphine CL using physiologically based pharmacokinetic (PBPK) modeling. The implementation of these three age-dependent factors into the pediatric system platform resulted in reasonable prediction for an age-dependent increase in morphine CL in these populations. Sensitivity of morphine CL to changes in cardiac output increased with age up to 3 years, whereas sensitivity to changes in UGT2B7 activity decreased. This study suggests that morphine exhibits age-dependent extraction, likely due to the developmental increase in OCT1 and UGT2B7 protein expression/activity and hepatic blood-flow.

Fentanyl Induces Cerebellar Internal Granular Cell Layer Apoptosis in Healthy Newborn Pigs

Background

Opioids like fentanyl are regularly used in neonates for analgesia and sedation. So far, they have been reported to be safe and eligible to use. The cerebellum has become a focus of neurodevelopmental research within the last years, as it is known to play an important role in long-lasting motor, cognitive, and other behavioral changes. The cerebellar cortex is of major importance in the coordinative role of the cerebellum and highly vulnerable to injury and impaired growth.

Objective

This study was performed to evaluate the apoptotic effect of intravenous fentanyl infusion on the cerebellum in healthy newborn pigs.

Methods

Thirteen healthy pigs (<median 12 h old) were randomized into (1) 24 h of intravenous fentanyl at normothermia (NTFe, n = 6) or (2) non-ventilated controls at normothermia (NTCTR, n = 7). Cerebellar sections were morphologically assessed after staining with hematoxylin–eosin. In addition, paired sections were immuno-stained for cell death [Cleaved caspase-3 and terminal deoxynucleotidyl transferase-mediated deoxyuridine-triphosphate nick-end labeling (TUNEL)], and positive cells were counted in defined areas of the internal granular cell layer. In total, cells in three cerebellar gyri were counted.

Results

We found that there was an increase in cells with apoptotic morphology in the internal granular cell layer in the NTFe group. For quantification, we found a significant increase in cell death in group (1) [median (range) number of caspase-3-positive cell group (1) 8 (1–22) vs. group (2) 1 (1–6) and TUNEL-positive cells (1) 6 (1–10) vs. (2) 1 (0–4)]. In both groups, there was no difference in the number of Purkinje cells. Both groups had comparable and stable physiological parameters throughout the 24 h period.

Conclusion

Twenty-four hours of continuous intravenous fentanyl infusion increased apoptosis in the internal granular cell layer in the cerebellum of healthy newborn pigs.

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.

[Pain therapy for premature babies and neonates]

Pain is a central topic on neonatal intensive care units (NICU). Acute as well as prolonged (continuous and chronic) pain frequently occurs. Due to a lack of validated physiological measurement instruments for pain (e. g. saliva cortisol, skin conductance and heart rate variability) pain in neonatology can only be assessed by external observation through the bedside team with pain scores using a regular, standardized procedure. During this very vulnerable period pain and medications (analgesics/sedatives) can negatively influence the brain development of premature babies and neonates. Therefore, limitation of the number of pain stimuli and the medicinal guideline "as much as necessary but as little as possible" are eminently important. When dealing with prolonged (continuous and chronic) pain, further challenges are a reduction of analgesics and sedatives as well as avoidance of withdrawal symptoms.

Multistep Unified Models Using Prior Knowledge for the Prediction of Drug Clearance in Neonates and Infants

Allometric approaches are widely used for interspecies scaling for the prediction of pharmacokinetic (PK) parameters during drug development. The concept of allometry can also be extended to predict PK parameters from adults to children. Three methods for extrapolating pediatric clearance were developed and evaluated using the clearance values of 4 drugs. The first method was established using a simple allometric (SA) model with estimated coefficient and exponent based on data ranging from children older than 2 years to adult. Then we developed a unified multistep single-exponent (MSE) and multistep body-weight-dependent exponent (MBDE) models. The major steps in these 2 new methods include generating pseudopredicted clearance for unobserved new populations such as preterm neonates, term neonates, and infants. Subsequent steps involve incorporating the pseudopredicted clearance with the actual PK data from older children and adults. All 3 models were then used to predict drug clearance in children ≤2 years old (N = 278). Drug clearance was predicted with mean absolute error of 29.6, 14.2, and 12.9 using SA, MSE, MBDE, respectively. The root mean square error was 65.9, 29.8, 24.7 for SA, MSE, MBDE, respectively. Approximately 41%, 72%, and 74% of the children's clearance data were within 0.5 to 1.5-fold of the observed values when drug clearance was extrapolated using SA, MSE, and MBDE models, respectively. The present multistep unified extrapolation approaches improved the prediction of clearance from preterm neonates to 2 years of age and may have practical use for first-in-pediatric dose selection.

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.

Predictive Performance of a Recently Developed Population Pharmacokinetic Model for Morphine and its Metabolites in New Datasets of (Preterm) Neonates, Infants and Children

BACKGROUND AND OBJECTIVE

Model validation procedures are crucial when models are to be used to develop new dosing algorithms. In this study, the predictive performance of a previously published paediatric population pharmacokinetic model for morphine and its metabolites in children younger than 3 years (original model) is studied in new datasets that were not used to develop the original model.

METHODS

Six external datasets including neonates and infants up to 1 year were obtained from four different research centres. These datasets contained postoperative patients, ventilated patients and patients on extracorporeal membrane oxygenation (ECMO) treatment. Basic observed versus predicted plots, normalized prediction distribution error analysis, model refitting, bootstrap analysis, subpopulation analysis and a literature comparison of clearance predictions were performed with the new datasets to evaluate the predictive performance of the original morphine pharmacokinetic model.

RESULTS

The original model was found to be stable and the parameter estimates were found to be precise. The concentrations predicted by the original model were in good agreement with the observed concentrations in the four datasets from postoperative and ventilated patients, and the model-predicted clearances in these datasets were in agreement with literature values. In the datasets from patients on ECMO treatment with continuous venovenous haemofiltration (CVVH) the predictive performance of the model was good as well, whereas underprediction occurred, particularly for the metabolites, in patients on ECMO treatment without CVVH.

CONCLUSION

The predictive value of the original morphine pharmacokinetic model is demonstrated in new datasets by the use of six different validation and evaluation tools. It is herewith justified to undertake a proof-of-principle approach in the development of rational dosing recommendations - namely, performing a prospective clinical trial in which the model-based dosing algorithm is clinically evaluated.

Pharmacologic Considerations of Anesthetic Agents in Pediatric Patients: A Comprehensive Review

Acute pain in the pediatric population has important differences in terms of biology, intrapopulation variation, and epidemiology. Discussion as to the pharmacologic considerations of anesthetic agents, such as induction agents, neuromuscular blockers, opioids, local anesthetics, and adjuvant agents, is presented in this article. Special considerations and concerns, such as risk for propofol infusion syndrome and adverse potential side effects of anesthesia agents, are discussed. Anesthesiologists managing pediatric patients need to have a firm understanding of physiologic and pharmacologic differences compared with the adult population. Future studies to improve the understanding of pharmacokinetics in the pediatric population are needed.

Morphine Pharmacodynamics in Mechanically Ventilated Preterm Neonates Undergoing Endotracheal Suctioning

To date, morphine pharmacokinetics (PKs) are well quantified in neonates, but results about its efficacy are ambiguous. This work presents an analysis of a previously published study on pain measurements in mechanically ventilated preterm neonates who received either morphine or placebo to improve comfort during invasive ventilation. The research question was whether morphine reduces the pain associated with endotracheal or nasal suctioning before, during, and after suctioning. Because these neonates cannot verbalize their pain levels, pain was assessed on the basis of several validated pain measurement instruments (i.e., COMFORT‐B, preterm infant pain profile [PIPP], Neonatal Infant Pain Scale (NIPS), and visual analogue scale (VAS)). The item response theory (IRT) was used to analyze the data in order for us to handle the data from multiple‐item pain scores. The analysis showed an intra‐individual relationship between morphine concentrations and pain reduction, as measured by COMFORT‐B and VAS. However, the small magnitude of the morphine effect was not considered clinically relevant for this intervention in preterm neonates.

Oral morphine dosing predictions based on single dose in healthy children undergoing surgery

BACKGROUND

Oral morphine has been proposed as an effective and safe alternative to codeine for after-discharge pain in children following surgery but there are few data guiding an optimum safe oral dose.

AIMS

The aim of this study was to characterize the absorption pharmacokinetics of enteral morphine in order to simulate time-concentration profiles in children given common oral morphine dose regimens.

METHODS

Children (2-6 years, n = 34) undergoing elective surgery and requiring opioid analgesia were randomized to receive preoperative oral morphine (100 mcg·kg^-1 , 200 mcg·kg^-1 , 300 mcg·kg^-1 ). Blood sampling for morphine assay was performed at 30, 60, 90, 120, 180, and 240 min. Morphine serum concentrations were determined by liquid chromatography-mass spectroscopy and pharmacokinetic parameters were calculated using nonlinear mixed effects models. Current data were pooled with published time-concentration profiles from children (n = 1059, age 23 weeks postmenstrual age - 3 years) administered intravenous morphine, to determine oral bioavailability (F), absorption lag time (T_LAG ), and absorption half-time (T_ABS ). These parameter estimates were used to predict concentrations in children given oral morphine (100, 200, 300, 400, 500 mcg·kg^-1 ) at different dosing intervals (3, 4, 5, 6, 8, 12 h).

RESULTS

The oral morphine formulation had F 0.298 (CV 36.5%), T_LAG 0.45 (CV 63.6%) h and T_ABS 0.71 (CV 55%) h. A single-dose morphine 100 mcg·kg^-1 achieved a mean C_MAX 10 mcg·l^-1 . Repeat 4-hourly dosing achieved mean steady-state concentration 13-18 mcg·l^-1 ; concentrations associated with good analgesia after intravenous administration. Serum concentration variability was large ranging from 5 to 55 mcg·l^-1 at steady state.

CONCLUSIONS

Oral morphine 200 mcg·kg^-1 then 100 mcg·kg^-1 4 h or 150 mcg·kg^-1 6 h achieves mean concentrations associated with analgesia. There was high serum concentration variability suggesting that respiration may be compromised in some children given these doses.

A blinded randomised placebo-controlled trial investigating the efficacy of morphine analgesia for procedural pain in infants: Trial protocol

Infant pain has both immediate and long-term negative consequences, yet in clinical practice it is often undertreated. To date, few pain-relieving drugs have been tested in infants. Morphine is a potent analgesic that provides effective pain relief in adults, but there is inconclusive evidence for its effectiveness in infants. The purpose of this study is to establish whether oral morphine provides effective analgesia for procedural pain in infants. A blinded, placebo-controlled, parallel-group randomized, phase II, clinical trial will be undertaken to determine whether morphine sulphate administered orally prior to clinically-required retinopathy of prematurity (ROP) screening and heel lancing provides effective analgesia. 
156 infants between 34 and 42 weeks' gestational age who require a clinical heel lance and ROP screening on the same test occasion will be included in the trial. Infants will be randomised to receive either a single dose of morphine sulphate (100 μg/kg) or placebo. Each infant will be monitored for 48 hours and safety data will be collected during the 24 hours following drug administration. The primary outcome will be the Premature Infant Pain Profile-revised (PIPP-R) score 30 seconds after ROP screening. The co-primary outcome will be the magnitude of nociceptive-specific brain activity evoked by a clinically-required heel lance. Infant clinical stability will be assessed by comparing the number of episodes of bradycardia, tachycardia, desaturation and apnoea, and changes in respiratory support requirements in the 24-hour periods before and after the clinical intervention. In addition, drug safety will be assessed by considering the occurrence of apnoeic and hypotensive episodes requiring intervention in the 24-hour period following drug administration. This study has been published as an Accepted Protocol Summary by The Lancet.