Pharmacodynamics and Pharmacokinetics of Morphine After Cardiac Surgery in Children With and Without Down Syndrome

Scoping Review of Paediatric Population Pharmacokinetic Models of Morphine

OBJECTIVE AND PURPOSE

This scoping review aimed to summarise all available population pharmacokinetic models of morphine and its metabolites (morphine-3-glucoronide [M3G], morphine-6-glucoronide [M6G]) in children and describe how morphine exposure varies across paediatric age groups and settings. Identifying the factors that contribute to pharmacokinetic variability may improve our understanding of a patient's pharmacodynamic response to morphine.

METHODS

We searched Embase and MEDLINE databases from inception to 8 March 2024 for paediatric population pharmacokinetic models of morphine and its metabolites. Two reviewers independently screened abstracts and full texts and extracted the data. The review was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines.

RESULTS

In total, 21 paediatric population pharmacokinetic models of morphine were identified; 12 studies also included morphine metabolites (M3G and/or M6G). Neonates and young children (< 6 years) were the most studied age groups (18/21; 86%), whereas older children (> 6 years) and adolescents (> 10 years) were included in only 6 of the 21 (29%) models. Morphine pharmacokinetics were most commonly described with two-compartment (52%) and one-compartment (38%) structure with first-order elimination. Several model covariates were identified: bodyweight, post-natal age for neonates, body temperature, therapeutic cooling, duration of mechanical ventilation, and genetic variation in drug transporters that mediate the uptake of morphine (e.g. OCT1).

CONCLUSION

Several population pharmacokinetic models of morphine and its metabolites in paediatrics have been published across diverse patient groups. Bodyweight and age-related covariates emerged as the most common factors affecting clearance and distribution; other covariates, including mechanical ventilation, therapeutic cooling, and genetic variation, also impacted morphine pharmacokinetics. Further research should focus on validating the predictive accuracy of paediatric morphine models in different patient populations and the combined effect of covariates, such as those related to critical illness and genetic variation, on morphine pharmacokinetics.

Opioid and benzodiazepine requirements in critically ill post-surgical children with down syndrome: a systematic review and meta-analysis

BACKGROUND

Down syndrome (DS), or Trisomy 21, is defined by the existence of an additional chromosome 21. Various physiological considerations in DS patients might lead to challenges in adequate pain management and sedation after surgery. The aim of this systematic review and meta-analysis is to evaluate the variations of the requirement needed for pain management and sedation in patients with DS who have undergone surgery compared to patients without DS.

METHODS

A systematic review and meta-analysis of studies were conducted, focusing on critically ill patients with DS who were admitted to Intensive care units (ICUs) post-surgery and received opioids and/or benzodiazepines. Searches were conducted in four databases from their inception to November 18, 2023 (Pubmed, Scopus, Cochrane Library, and Web of Science). The primary outcome measured was the dosage of Oral Morphine Equivalent (OME) administered in the days following surgery. Fixed-effect models were used, an approach advisable when only a limited number of studies are available.

RESULTS

Out of the 992 studies initially screened, the systematic review included ten studies, encompassing 730 patients, while the meta-analysis consisted of seven studies, encompassing 533 patients. Of the seven studies included in the analysis, 298 patients were identified to have DS, and 235 patients served as controls. Patients with DS showed a slight increase in OME needs on the first day, but this increase was not statistically significant (mean difference [MD] = 0.09; 95% Confidence Interval [CI]: [-0.02, 0.20]; P = 0.11). There was also no significant difference in the requirement for Midazolam on the first day among DS patients (MD = 0.01; CI [-0.16, 0.19]; P = 0.88). In addition, the duration of mechanical ventilation was not statistically significant in patients with DS compared with the control group (MD = -1.46 hours; 95% CI [-9.74, 6.82]; P = 0.73).

CONCLUSION

Patients with Down syndrome did not require more sedation or analgesia in the first three days after surgery than patients without Down syndrome. Additionally, the two groups showed no significant difference in the duration of mechanical ventilation.

Intermittent intravenous paracetamol versus continuous morphine in infants undergoing cardiothoracic surgery: a multi-center randomized controlled trial

BACKGROUND

To determine whether intermittent intravenous (IV) paracetamol as primary analgesic would significantly reduce morphine consumption in children aged 0-3 years after cardiac surgery with cardiopulmonary bypass.

METHODS

Multi-center, randomized, double-blinded, controlled trial in four level-3 Pediatric Intensive Care Units (PICU) in the Netherlands and Belgium. Inclusion period; March 2016-July 2020. Children aged 0-3 years, undergoing cardiac surgery with cardiopulmonary bypass were eligible. Patients were randomized to continuous morphine or intermittent IV paracetamol as primary analgesic after a loading dose of 100 mcg/kg morphine was administered at the end of surgery. Rescue morphine was given if numeric rating scale (NRS) pain scores exceeded predetermined cutoff values. Primary outcome was median weight-adjusted cumulative morphine dose in mcg/kg in the first 48 h postoperative. For the comparison of the primary outcome between groups, the nonparametric Van Elteren test with stratification by center was used. For comparison of the proportion of patients with one or more NRS pain scores of 4 and higher between the two groups, a non-inferiority analysis was performed using a non-inferiority margin of 20%.

RESULTS

In total, 828 were screened and finally 208 patients were included; parents of 315 patients did not give consent and 305 were excluded for various reasons. Fourteen of the enrolled 208 children were withdrawn from the study before start of study medication leaving 194 patients for final analysis. One hundred and two patients received intermittent IV paracetamol, 106 received continuous morphine. The median weight-adjusted cumulative morphine consumption in the first 48 h postoperative in the IV paracetamol group was 5 times lower (79%) than that in the morphine group (median, 145.0 (IQR, 115.0-432.5) mcg/kg vs 692.6 (IQR, 532.7-856.1) mcg/kg; P < 0.001). The rescue morphine consumption was similar between the groups (p = 0.38). Non-inferiority of IV paracetamol administration in terms of NRS pain scores was proven; difference in proportion - 3.1% (95% CI - 16.6-10.3%).

CONCLUSIONS

In children aged 0-3 years undergoing cardiac surgery, use of intermittent IV paracetamol reduces the median weight-adjusted cumulative morphine consumption in the first 48 h after surgery by 79% with equal pain relief showing equipoise for IV paracetamol as primary analgesic. Trial Registration Clinicaltrials.gov, Identifier: NCT05853263; EudraCT Number: 2015-001835-20.

Perspectives on pain in Down syndrome

Down syndrome (DS) or trisomy 21 is a genetic condition often accompanied by chronic pain caused by congenital abnormalities and/or conditions, such as osteoarthritis, recurrent infections, and leukemia. Although DS patients are more susceptible to chronic pain as compared to the general population, the pain experience in these individuals may vary, attributed to the heterogenous structural and functional differences in the central nervous system, which might result in abnormal pain sensory information transduction, transmission, modulation, and perception. We tried to elaborate on some key questions and possible explanations in this review. Further clarification of the mechanisms underlying such abnormal conditions induced by the structural and functional differences is needed to help pain management in DS patients.

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.

Down Syndrome: A Review of Key Perioperative Implications

Down syndrome (DS) is the most common chromosomal abnormality in humans that is compatible with life. This syndrome occurs when there is an extra copy of the 21st chromosome. Down syndrome is associated with numerous comorbidities that can pose challenges for the perioperative nurse caring for a patient with DS undergoing surgery. These challenges can affect the patient assessment, communication with the patient, and patient safety (eg, preventing complications). As the life expectancy of people with DS has increased, so too have the chances that perioperative nurses will care for a patient with this disorder. This article reviews the pathophysiology of DS, discusses common comorbidities that may directly affect perioperative care, and reviews an exemplar case study that demonstrates how personnel with knowledge of DS can positively influence surgical team decision making for these patients in the perioperative setting.

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.

Dosing of Opioid Medications During and After Pediatric Cardiac Surgery for Children With Down Syndrome

OBJECTIVE

To determine whether children with Down syndrome (DS) receive higher doses of opioid medications compared with children without DS for repair of complete atrioventricular canal (CAVC).

DESIGN

A retrospective chart review of children with and without DS who underwent primary repair of CAVC. The exclusion criteria included unbalanced CAVC and patients undergoing biventricular staging procedures. The primary outcome was oral morphine equivalents (OME) received in the first 24 hours after surgery. The secondary outcomes included intraoperative OME, OME at 48 and 72 hours, nonopioid analgesic and sedative medications received, pain scores, time to extubation, and length of stay.

SETTING

A pediatric academic medical center in the United States.

PARTICIPANTS

One hundred thirty-one patients with DS and 24 without, all <two years old, who underwent a CAVC repair.

INTERVENTIONS

Not applicable.

MEASUREMENTS AND MAIN RESULTS

Patients with DS were older than patients without DS (median 96.3 days [interquartile range {IQR} 70.7-128.2] v 75.9 days [IQR 49.8-107.3], p = 0.033) but otherwise not statistically different in the baseline characteristics. There was no difference in OME received in the first 24 hours postoperatively between groups (3.01 mg/kg [IQR 1.23-5.43] v 3.57 mg/kg [IQR 1.54-7.06], p = 0.202). OME at 48 and 72 hours was lower in the DS group compared with the control group. Similar amounts of opioid and non-opioid analgesics and sedatives were otherwise given to both groups of patients. Median pain scores did not differ between groups.

CONCLUSIONS

These results suggested that patients with DS undergoing CAVC repair do not have increased opioid requirements compared with a similar control group.

Status Toward the Implementation of Precision Dosing in Children

Precision dosing is progressing beyond the conceptual and proof-of-concept stages toward implementation. As the availability of dosing algorithms, tools, and platforms increases, so do the investment in technology services and actual implementation of clinical services offering these solutions to patients. Nowhere is this needed more than in pediatric populations, which are still reliant on adult drug development and bridging strategies to support dosing, often in the absence of actual dose-finding studies in the target pediatric population. Still, there is more work to be done to ensure that proper governance of these services is maintained, and that sustainability of these early implementations is guided by new science as it evolves and meaningful outcome data to confirm that such services deliver on both clinical and economic return on investment. In addition, the field should ensure that all approaches beyond a therapeutic drug monitoring-driven, pharmacokinetic-centric approach should be considered as the tools and services evolve, especially when pediatric-specific pharmacokinetic/pharmacodyamic and pharmacogenetic data are available and shown to be useful to guide dosing. This review evaluates current pediatric precision dosing efforts, highlighting their utility, longevity, and sustainability and assesses the current process for implementing such approaches examining current barriers that stand in the way of broader implementation and the stakeholders that must engage to ensure its ultimate success.

A systematic review of the evidence supporting post-operative medication use in congenital heart disease

BACKGROUND

Targeted drug development efforts in patients with CHD are needed to standardise care, improve outcomes, and limit adverse events in the post-operative period. To identify major gaps in knowledge that can be addressed by drug development efforts and provide a rationale for current clinical practice, this review evaluates the evidence behind the most common medication classes used in the post-operative care of children with CHD undergoing cardiac surgery with cardiopulmonary bypass.

METHODS

We systematically searched PubMed and EMBASE from 2000 to 2019 using a controlled vocabulary and keywords related to diuretics, vasoactives, sedatives, analgesics, pulmonary vasodilators, coagulation system medications, antiarrhythmics, steroids, and other endocrine drugs. We included studies of drugs given post-operatively to children with CHD undergoing repair or palliation with cardiopulmonary bypass.

RESULTS

We identified a total of 127 studies with 51,573 total children across medication classes. Most studies were retrospective cohorts at single centres. There is significant age- and disease-related variability in drug disposition, efficacy, and safety.

CONCLUSION

In this study, we discovered major gaps in knowledge for each medication class and identified areas for future research. Advances in data collection through electronic health records, novel trial methods, and collaboration can aid drug development efforts in standardising care, improving outcomes, and limiting adverse events in the post-operative period.

Down syndrome and congenital heart disease: perioperative planning and management

Approximately 50% of newborns with Down syndrome have congenital heart disease. Non-cardiac comorbidities may also be present. Many of the principles and strategies of perioperative evaluation and management for patients with congenital heart disease apply to those with Down syndrome. Nevertheless, careful planning for cardiac surgery is required, evaluating for both cardiac and noncardiac disease, with careful consideration of the risk for pulmonary hypertension. In this manuscript, for children with Down syndrome and hemodynamically significant congenital heart disease, we will summarize the epidemiology of heart defects that warrant intervention. We will review perioperative planning for this unique population, including anesthetic considerations, common postoperative issues, nutritional strategies, and discharge planning. Special considerations for single ventricle palliation and heart transplantation evaluation will also be discussed. Overall, the risk of mortality with cardiac surgery in pediatric patients with Down syndrome is no more than the general population, except for those with functional single ventricle heart defects. Underlying comorbidities may contribute to postoperative complications and increased length of stay. A strong understanding of cardiac and non-cardiac considerations in children with Down syndrome will help clinicians optimize perioperative care and long-term outcomes.

Sedation With Midazolam After Cardiac Surgery in Children With and Without Down Syndrome: A Pharmacokinetic-Pharmacodynamic Study

OBJECTIVES

To compare the pharmacokinetics and pharmacodynamics of IV midazolam after cardiac surgery between children with and without Down syndrome.

DESIGN

Prospective, single-center observational trial.

SETTING

PICU in a university-affiliated pediatric teaching hospital.

PATIENTS

Twenty-one children with Down syndrome and 17 without, 3-36 months, scheduled for cardiac surgery with cardiopulmonary bypass.

INTERVENTIONS

Postoperatively, nurses regularly assessed the children's pain and discomfort with the validated COMFORT-Behavioral scale and Numeric Rating Scale for pain. A loading dose of morphine (100 µg/kg) was administered after coming off bypass; thereafter, morphine infusion was commenced at 40 µg/kg/hr. Midazolam was started if COMFORT-Behavioral scale score of greater than 16 and Numeric Rating Scale score of less than 4 (suggestive of undersedation). Plasma midazolam and metabolite concentrations were measured for population pharmacokinetic- and pharmacodynamic analysis using nonlinear mixed effects modeling (NONMEM) (Version VI; GloboMax LLC, Hanover, MD) software.

MEASUREMENTS AND MAIN RESULTS

Twenty-six children (72%) required midazolam postoperatively (15 with Down syndrome and 11 without; p = 1.00). Neither the cumulative midazolam dose (p = 0.61) nor the time elapsed before additional sedation was initiated (p = 0.71), statistically significantly differed between children with and without Down syndrome. Population pharmacokinetic and pharmacodynamics analysis revealed no statistically significant differences between the children with and without Down syndrome. Bodyweight was a significant covariate for the clearance of 1-OH-midazolam to 1-OH-glucuronide (p = 0.003). Pharmacodynamic analysis revealed a marginal effect of the midazolam concentration on the COMFORT-Behavioral score.

CONCLUSIONS

The majority of children with and without Down syndrome required additional sedation after cardiac surgery. This pharmacokinetic and pharmacodynamic analysis does not provide evidence for different dosing of midazolam in children with Down syndrome after cardiac surgery.

The impact of introducing nurse-led analgesia and sedation guidelines in ventilated infants following cardiac surgery

INTRODUCTION

Enhanced clinical outcomes in the Paediatric Intensive Care Unit following standardisation of analgesia and sedation practice are reported. Little is known about the impact of standardisation of analgesia and sedation practice including incorporation of a validated distress assessment instrument on infants post cardiac surgery, a subset of whom have Trisomy 21. This study investigated whether the parallel introduction of nurse-led analgesia and sedation guidelines including regular distress assessment would impact on morphine administered to infants post cardiac surgery, and whether any differences observed would be amplified within the Trisomy 21 population.

METHODOLOGY

A retrospective single centre before/after study design was used. Patients aged between 44 weeks postconceptual age and one year old who had open cardiothoracic surgery were included.

RESULTS

61 patients before and 64 patients after the intervention were included. After the intervention, a reduction in the amount of morphine administered was not evident, while greater use of adjuvant sedatives and analgesics was observed. Patients with Trisomy 21 had a shorter duration of mechanical ventilation after the change in practice.

CONCLUSION

The findings from this study affirm the importance of the nurses' role in managing prescribed analgesia and sedation supported by best available evidence. A continued education and awareness focus on analgesia and sedation management in the pursuit of best patient care is imperative.

Exploring the Relationship Between Morphine Concentration and Oversedation in Children After Cardiac Surgery

Titrating analgesic and sedative drugs in pediatric intensive care remains a challenge for caregivers due to the lack of pharmacodynamic knowledge in this population. The aim of the current study is to explore the concentration‐effect relationship for morphine‐associated oversedation after cardiac surgery in children aged 3 months to 3 years. Data on morphine dosing, as well as morphine plasma concentrations, were available from a previous study on the pharmacokinetics of morphine after cardiac surgery in children. Oversedation was defined as scores below 11 on the validated COMFORT–behavioral scale. Population pharmacokinetic‐pharmacodynamic modeling was performed in NONMEM 7.3. The probability of oversedation as a function of morphine concentration was best described using a step function in which the EC₅₀ was 46.3 ng/mL. At morphine concentrations below the EC₅₀, the probability of oversedation was 2.9% (0.4& to 18%), whereas above the EC₅₀ percentages were 13% (1.9% to 52%) (median value [95% prediction interval from interindividual variability]). Additionally, the risk of oversedation was found to be increased during the first hours after surgery (P < .001) and was significantly lower during mechanical ventilation (P < .005). We conclude that morphine concentrations above approximately 45 ng/mL may increase the probability of oversedation in children after cardiac surgery. The clinician must evaluate, on a case‐by‐case basis, whether the analgesic benefits arising from dosing regimen associated with such concentrations outweigh the risks.

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.

Down Syndrome and Postoperative Complications in Children Undergoing Intestinal Operations

OBJECTIVE

This paper intends to evaluate the association between Down Syndrome (DS) and postoperative medical and surgical complications and inpatient postoperative mortality in pediatric patients undergoing intestinal operations.

METHODS

The 2012 Kids' Inpatient Database was queried to compare short-term postoperative medical and surgical complications and in-patient mortality among patients with DS undergoing intestinal operations to a cohort without DS using inverse probability weighting. Subset analysis was performed for patients undergoing intestinal operations exclusive of gastrostomy placement. Adverse treatment effects were calculated for the outcomes of interest.

RESULTS

Of 17,026 pediatric patients undergoing intestinal operations, 444 had DS. In unadjusted analysis, medical complications (urinary tract infection, deep venous thrombosis, sepsis, pneumonia) occurred in 7.9% of patients with DS, compared to 14.1% of those without (p < 0.001). Surgical complications (wound disruption, hemorrhage, superficial or deep wound infection) occurred in 3.5% of patients with DS, compared to 4.6% of those without (p = 0.34), and in-patient mortality occurred in 0.3% of patients with DS, compared to 2.7% of those without (p = 0.009). Adverse treatment effects (ATE) calculated after inverse probability weighting demonstrated no difference for medical or surgical complications but a significantly decreased mortality with DS.

CONCLUSIONS

Contrary to common perception and data extrapolated from the adult literature, pediatric patients with DS have neither higher medical nor surgical complication rates after intestinal operations. Similar to patients undergoing congenital heart surgery, pediatric patients with DS have a lower postoperative inpatient mortality after these general operations compared to those without DS. Mechanisms influencing risks in DS patient remain unknown.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Population Pharmacokinetic Modeling of Acetaminophen and Metabolites in Children After Cardiac Surgery With Cardiopulmonary Bypass

Children undergoing cardiac surgery often receive acetaminophen (paracetamol) as part of their postoperative pain treatment. To date, there is no information on the pharmacokinetics (PK) of acetaminophen in this special population, even though differences, as a result of altered hemodynamics and/or use of cardiopulmonary bypass, may be anticipated. Therefore, the aim of this study was to investigate the PK of intravenous acetaminophen in children after cardiac surgery with cardiopulmonary bypass. In the study, both children with and without Down syndrome were included. A population PK analysis, using NONMEM 7.2, was performed based on 161 concentrations of acetaminophen, acetaminophen sulfate, acetaminophen glucuronide, and oxidative metabolites from 17 children with Down syndrome and 13 children without Down syndrome of a previously published study (median age, 177 days [range, 92-944], body weight, 6.1 kg [4.0-12.9]). All children received 3 intravenous acetaminophen doses of 7.5 mg/kg (<10 kg) or 15 mg/kg (≥10 kg) at 8-hour intervals after cardiac surgery. For acetaminophen and its metabolites, 1-compartment models were identified. Clearance of acetaminophen and metabolites increased linearly with body weight. Acetaminophen clearance in a typical child of 6.1 kg is 0.96 L/h and volume of distribution 7.96 L. Down syndrome did not statistically significantly impact any of the PK parameters for acetaminophen, nor did any other remaining covariate. When comparing the PK parameters of acetaminophen in children after cardiac surgery with cardiopulmonary bypass with those from children of the same age following noncardiac surgery reported in the literature, clearance of acetaminophen was lower and volume of distribution higher.

Influence of Morbid Obesity on the Pharmacokinetics of Morphine, Morphine-3-Glucuronide, and Morphine-6-Glucuronide

Introduction

Obesity is associated with many pathophysiological changes that may result in altered drug metabolism. The aim of this study is to investigate the influence of obesity on the pharmacokinetics of morphine, morphine-3-glucuronide (M3G), and morphine-6-glucuronide (M6G) through a combined analysis in morbidly obese patients and non-obese healthy volunteers.

Methods

In this analysis, data from 20 morbidly obese patients [mean body mass index 49.9 kg/m² (range 37.6–78.6 kg/m²) and weight 151.3 kg (range 112–251.9 kg)] and 20 healthy volunteers [mean weight 70.6 kg (range 58–85 kg)] were included. Morbidly obese patients received 10 mg of intravenous (I.V.) morphine after gastric bypass surgery, with additional morphine I.V. doses as needed. Healthy volunteers received an I.V. bolus of morphine of 0.1 mg/kg followed by an infusion of 0.030 mg kg⁻¹ h⁻¹ for 1 h. Population pharmacokinetic modeling was performed using NONMEM 7.2.

Results

In morbidly obese patients, elimination clearance of M3G and M6G was decreased substantially compared with healthy volunteers (p < 0.001). Regarding glucuronidation, only a slight decrease in the formation of M6G and a delay in the formation of M3G was found (both p < 0.001). Obesity was also identified as a covariate for the peripheral volume of distribution of morphine (p < 0.001).

Conclusion

Metabolism of morphine is not altered in morbidly obese patients. However, decreased elimination of both M3G and M6G is evident, resulting in a substantial increase in exposure to these two metabolites. A rational explanation of this finding is that it results from alterations in membrane transporter function and/or expression in the liver.

ClinicalTrials.gov identifier: NCT01097148.

Electronic supplementary material

The online version of this article (doi:10.1007/s40262-017-0544-2) contains supplementary material, which is available to authorized users.

Intravenous morphine versus intravenous paracetamol after cardiac surgery in neonates and infants: a study protocol for a randomized controlled trial

BACKGROUND

Morphine is worldwide the analgesic of first choice after cardiac surgery in children. Morphine has unwanted hemodynamic and respiratory side effects. Therefore, post-cardiac surgery patients may potentially benefit from a non-opioid drug for pain relief. A previous study has shown that intravenous (IV) paracetamol is effective and opioid-sparing in children after major non-cardiac surgery. The aim of the study is to test the hypothesis that intermittent IV paracetamol administration in children after cardiac surgery will result in a reduction of at least 30% of the cumulative morphine requirement.

METHODS

This is a prospective, multi-center, randomized controlled trial at four level-3 pediatric intensive care units (ICUs) in the Netherlands and Belgium. Children who are 0-36 months old will be randomly assigned to receive either intermittent IV paracetamol or continuous IV morphine up to 48 h post-operatively. Morphine will be available as rescue medication for both groups. Validated pain and sedation assessment tools will be used to monitor patients. The sample size (n = 208, 104 per arm) was calculated in order to detect a 30% reduction in morphine dose; two-sided significance level was 5% and power was 95%.

DISCUSSION

This study will focus on the reduction, or replacement, of morphine by IV paracetamol in children (0-36 months old) after cardiac surgery. The results of this study will form the basis of a new pain management algorithm and will be implemented at the participating ICUs, resulting in an evidence-based guideline on post-operative pain after cardiac surgery in infants who are 0-36 months old.

TRIAL REGISTRATION

Dutch Trial Registry ( www.trialregister.nl ): NTR5448 on September 1, 2015. Institutional review board approval (MEC2015-646), current protocol version: July 3, 2017.

Potentially clinically relevant concentrations of Cefazolin, Midazolam, Propofol, and Sufentanil in auto-transfused blood in congenital cardiac surgery

Background

Use of donor blood in congenital cardiac surgery increases the risk for post-operative morbidity and mortality. To reduce the need for allogenic blood transfusion a technique for peri-operative mechanical red cell salvage is applied. Blood from the operation site is collected in a reservoir, processed, passed through a lipophilic filter and returned to the patient. Influence of this cellsaver system on coagulation, fibrinolysis and inflammatory markers is known. To our knowledge no studies have been performed on the effects of autotransfusion on drug concentrations. A clinically relevant drug dose could potentially be returned to the patient through the auto-transfused blood, leading to unwanted drug reactions post-operatively. We aimed to measure drug concentrations in blood salvaged from the operation site and in the auto-transfused blood to determine if a clinically relevant drug dose is returned to the patient.

Methods

The study was performed at the Department of Cardiothoracic Surgery of a tertiary university hospital. Blood samples were taken from the reservoir, after processing before the lipophilic filter, the auto-transfused blood, and the waste fluid. Samples were stored at − 80 C and drug concentration for sufentanil, propofol, midazolam and cefazolin were measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Drug concentrations measured in the reservoir and the auto-transfused blood were compared and the relative reduction was calculated for each patient.

Results

Blood samples were taken from 18 cellsaver runs in 18 patients, age 0–13 years. Drug concentrations in the reservoir were comparable to concomitant concentrations in the patient. For sufentanil 34% (median, IQR 27–50) of drug concentration was retained from the reservoir in the auto-transfused blood, for midazolam 6% (median, IQR 4–10), for cefazolin 5% (median, IQR 2–6) and for propofol 0% (median, IQR 0–0) respectively.

Conclusion

Depending on the drug, up to 34% of the drug concentration salvaged from the operation site is returned to the patient through autotransfusion, potentially causing unwanted drug reactions post-operatively. Additionally, influence of a cellsaver system should be considered in pharmacological research during and after congenital cardiac surgery and could result in dose adjustments in the postoperative phase.

Trial registration

Registration at the Dutch Trial Registry (NTR3579) at August 14 2012.

Morphine Pharmacokinetics in Children With Down Syndrome Following Cardiac Surgery

OBJECTIVES

To assess if morphine pharmacokinetics are different in children with Down syndrome when compared with children without Down syndrome.

DESIGN

Prospective single-center study including subjects with Down syndrome undergoing cardiac surgery (neonate to 18 yr old) matched by age and cardiac lesion with non-Down syndrome controls. Subjects were placed on a postoperative morphine infusion that was adjusted as clinically necessary, and blood was sampled to measure morphine and its metabolites concentrations. Morphine bolus dosing was used as needed, and total dose was tracked. Infusions were continued for 24 hours or until patients were extubated, whichever came first. Postinfusion, blood samples were continued for 24 hours for further evaluation of kinetics. If patients continued to require opioid, a nonmorphine alternative was used. Morphine concentrations were determined using a unique validated liquid chromatography tandem-mass spectrometry assay using dried blood spotting as opposed to large whole blood samples. Morphine concentration versus time data was modeled using population pharmacokinetics.

SETTING

A 16-bed cardiac ICU at an university-affiliated hospital.

PATIENTS

Forty-two patients (20 Down syndrome, 22 controls) were enrolled.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The pharmacokinetics of morphine in pediatric patients with and without Down syndrome following cardiac surgery were analyzed. No significant difference was found in the patient characteristics or variables assessed including morphine total dose or time on infusion. Time mechanically ventilated was longer in children with Down syndrome, and regarding morphine pharmacokinetics, the covariates analyzed were age, weight, presence of Down syndrome, and gender. Only age was found to be significant.

CONCLUSIONS

This study did not detect a significant difference in morphine pharmacokinetics between Down syndrome and non-Down syndrome children with congenital heart disease.

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.

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.

Predicting CYP3A-mediated midazolam metabolism in critically ill neonates, infants, children and adults with inflammation and organ failure

AIMS

Inflammation and organ failure have been reported to have an impact on cytochrome P450 (CYP) 3A-mediated clearance of midazolam in critically ill children. Our aim was to evaluate a previously developed population pharmacokinetic model both in critically ill children and other populations, in order to allow the model to be used to guide dosing in clinical practice.

METHODS

The model was evaluated externally in 136 individuals, including (pre)term neonates, infants, children and adults (body weight 0.77-90 kg, C-reactive protein level 0.1-341 mg l^-1 and 0-4 failing organs) using graphical and numerical diagnostics.

RESULTS

The pharmacokinetic model predicted midazolam clearance and plasma concentrations without bias in postoperative or critically ill paediatric patients and term neonates [median prediction error (MPE) <30%]. Using the model for extrapolation resulted in well-predicted clearance values in critically ill and healthy adults (MPE <30%), while clearance in preterm neonates was over predicted (MPE >180%).

CONCLUSION

The recently published pharmacokinetic model for midazolam, quantifying the influence of maturation, inflammation and organ failure in children, yields unbiased clearance predictions and can therefore be used for dosing instructions in term neonates, children and adults with varying levels of critical illness, including healthy adults, but not for extrapolation to preterm neonates.

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.

Paracetamol and morphine for infant and neonatal pain; still a long way to go?

INTRODUCTION

Pharmacologic pain management in newborns and infants is often based on limited scientific data. To close the knowledge gap, drug-related research in this population is increasingly supported by the authorities, but remains very challenging. This review summarizes the challenges of analgesic studies in newborns and infants on morphine and paracetamol (acetaminophen). Areas covered: Aspects such as the definition and multimodal character of pain are reflected to newborn infants. Specific problems addressed include defining pharmacodynamic endpoints, performing clinical trials in this population and assessing developmental changes in both pharmacokinetics and pharmacodynamics. Expert commentary: Neonatal and infant pain management research faces two major challenges: lack of clear biomarkers and very heterogeneous pharmacokinetics and pharmacodynamics of analgesics. There is a clear call for integral research addressing the multimodality of pain in this population and further developing population pharmacokinetic models towards physiology-based models.