Steady-state plasma concentrations of midazolam in critically ill infants and children

The effect of age on outpatient pediatric procedural sedation with intranasal dexmedetomidine and oral midazolam

Procedural sedation for diagnostic examination is a common practice in children. The study aims to analyze the sedative effect and safety of intranasal dexmedetomidine combined with oral midazolam in outpatient pediatric procedural sedation across different age groups and to assess the incidence of sedation failure. From February 2021 to September 2021, children who underwent procedural sedation were retrospectively enrolled. The children were divided into 4 groups based on age: the infant group (0 to 1 year old), toddler group (1 to 3 years old), preschool group (3 to 6 years old), and school-age group (6 to 12 years old). Two-mcg/kg intranasal dexmedetomidine and 0.5-mg/kg oral midazolam were used for sedation. The sedation success rate after rescue, sedation success rate, onset time of sedation, and the sedation time were recorded. The incidence of adverse events and the risk factors for sedation failure were also analyzed. A total of 4758 patients were identified. After exclusion, 3149 patients were ultimately enrolled. The combination of 2-mcg/kg intranasal dexmedetomidine and 0.5-mg/kg oral midazolam resulted in a total success rate of 99.7% and a sedation success rate of 91.4%. The sedation success rate varied among the four groups: 90.2% in the infant group, 93.1% in the toddler group, 92.7% in the preschool group, and 78.4% in the school-age group. The sedation success rate was significantly lower in the school-age group compared to the other three groups (P < 0.001). The onset time of sedation was shorter in infant (22 min, IQR: 18-28 min, P < 0.001) and longer in the school-age group (30 min, IQR: 25-35 min, P < 0.05). Additionally, the infants had a longer sedation time (110 min, IQR: 90-135 min, P < 0.001) and a higher rate of delayed recovery (27.5%, all P < 0.001). The incidence of adverse events was low (4.70%), which bradycardia (2.03%) being the most common. Age (0-1 year and > 6 years), weight, ASA class II, and history of failed sedation were identified as risk factors of sedation failure.   Conclusion: Intranasal administration of 2-mcg/kg dexmedetomidine combined with oral administration of 0.5-mg/kg midazolam was found to be efficient and safety for pediatric procedural sedation. Different age groups of children exhibited distinct sedation characteristics, and age was identified as a risk factor affecting the efficacy of sedation. What is Known: • Procedural sedation for diagnostic examination is a common practice in children. • The combination of dexmedetomidine with midazolam can improve sedative effects. What is New: • The success rate of sedation using a combination of 2-mcg/kg intranasal dexmedetomidine and 0.5-mg/kg oral midazolam was significantly lower in school-age children as compared to infants, toddlers, and preschoolers. • The onset time of sedation increased with age, and the sedation time was found to be longer in infant patients.

Inflammation and cardiovascular status impact midazolam pharmacokinetics in critically ill children: An observational, prospective, controlled study

Altered physiology caused by critical illness may change midazolam pharmacokinetics and thereby result in adverse reactions and outcomes in this vulnerable patient population. This study set out to determine which critical illness-related factors impact midazolam pharmacokinetics in children using population modeling. This was an observational, prospective, controlled study of children receiving IV midazolam as part of routine care. Children recruited into the study were either critically-ill receiving continuous infusions of midazolam or otherwise well, admitted for elective day-case surgery (control) who received a single IV bolus dose of midazolam. The primary outcome was to determine the population pharmacokinetics and identify covariates that influence midazolam disposition during critical illness. Thirty-five patients were recruited into the critically ill arm of the study, and 54 children into the control arm. Blood samples for assessing midazolam and 1-OH-midazolam concentrations were collected opportunistically (critically ill arm) and in pre-set time windows (control arm). Pharmacokinetic modeling demonstrated a significant change in midazolam clearance with acute inflammation (measured using C-Reactive Protein), cardio-vascular status, and weight. Simulations predict that elevated C-Reactive Protein and compromised cardiovascular function in critically ill children result in midazolam concentrations up to 10-fold higher than in healthy children. The extremely high concentrations of midazolam observed in some critically-ill children indicate that the current therapeutic dosing regimen for midazolam can lead to over-dosing. Clinicians should be aware of this risk and intensify monitoring for oversedation in such patients.

Pharmacogenomic associations of cyclophosphamide pharmacokinetic candidate genes with event-free survival in intermediate-risk rhabdomyosarcoma: A report from the Children's Oncology Group

BACKGROUND

In vitro data suggest that the growth of rhabdomyosarcoma (RMS) cells is suppressed in a concentration-dependent manner by 4-hydroxycyclophosphamide (4HCY), the principal precursor to the cytotoxic metabolite of cyclophosphamide (CY). Various retrospective studies on the relationship between genes encoding proteins involved in the formation and elimination of 4HCY (i.e., 4HCY pharmacokinetics) and cyclophosphamide (CY) efficacy and toxicity have been conflicting.

PROCEDURES

We evaluated germline pharmacogenetics in 262 patients with newly diagnosed intermediate-risk RMS who participated in one prospective Children's Oncology Group clinical trial, ARST0531. Patients were treated with either vincristine/actinomycin/cyclophosphamide (VAC) or VAC alternating with vincristine/irinotecan (VAC/VI). We analyzed the associations between event-free survival and 394 single-nucleotide polymorphisms (SNP) in 14 drug metabolizing enzymes or transporters involved in 4HCY pharmacokinetics.

RESULTS

Eight SNPs were associated (p-value < .05 by univariate analysis) with 3-year event-free survival; no SNPs survived a false discovery rate < 0.05.

CONCLUSIONS

Our data suggest that a pharmacogenomic approach to therapy personalization of cyclophosphamide in intermediate-risk rhabdomyosarcoma is not viable. Other methods to personalize therapy should be explored.

Midazolam Dose Optimization in Critically Ill Pediatric Patients With Acute Respiratory Failure: A Population Pharmacokinetic-Pharmacogenomic Study

OBJECTIVES

To develop a pharmacokinetic-pharmacogenomic population model of midazolam in critically ill children with primary respiratory failure.

DESIGN

Prospective pharmacokinetic-pharmacogenomic observational study.

SETTING

Thirteen PICUs across the United States.

PATIENTS

Pediatric subjects mechanically ventilated for acute respiratory failure, weight greater than or equal to 7 kg, receiving morphine and/or midazolam continuous infusions.

INTERVENTIONS

Serial blood sampling for drug quantification and a single blood collection for genomic evaluation.

MEASUREMENTS AND MAIN RESULTS

Concentrations of midazolam, the 1' (1`-hydroxymidazolam metabolite) and 4' (4`-hydroxymidazolam metabolite) hydroxyl, and the 1' and 4' glucuronide metabolites were measured. Subjects were genotyped using the Illumina HumanOmniExpress genome-wide single nucleotide polymorphism chip. Nonlinear mixed effects modeling was performed to develop the pharmacokinetic-pharmacogenomic model. Body weight, age, hepatic and renal functions, and the UGT2B7 rs62298861 polymorphism are relevant predictors of midazolam pharmacokinetic variables. The estimated midazolam clearance was 0.61 L/min/70kg. Time to reach 50% complete mature midazolam and 1`-hydroxymidazolam metabolite/4`-hydroxymidazolam metabolite clearances was 1.0 and 0.97 years postmenstrual age. The final model suggested a decrease in midazolam clearance with increase in alanine transaminase and a lower clearance of the glucuronide metabolites with a renal dysfunction. In the pharmacogenomic analysis, rs62298861 and rs28365062 in the UGT2B7 gene were in high linkage disequilibrium. Minor alleles were associated with a higher 1`-hydroxymidazolam metabolite clearance in Caucasians. In the pharmacokinetic-pharmacogenomic model, clearance was expected to increase by 10% in heterozygous and 20% in homozygous for the minor allele with respect to homozygous for the major allele.

CONCLUSIONS

This work leveraged available knowledge on nonheritable and heritable factors affecting midazolam pharmacokinetic in pediatric subjects with primary respiratory failure requiring mechanical ventilation, providing the basis for a future implementation of an individual-based approach to sedation.

Maturation of midazolam clearance in critically ill children with severe bronchiolitis: A population pharmacokinetic analysis

PURPOSE

The aim of the present study was to develop a population pharmacokinetic model of midazolam, and to evaluate the influence of maturation process and other variability factors in critically ill children with severe acute bronchiolitis, who received a long-term intravenous infusion of midazolam.

METHODS

In the study were included 49 critically ill children of both genders (from 0 to 130 weeks of age) with severe acute bronchiolitis hospitalised in intensive care units. Nonlinear mixed effects modelling approach was applied for data analyses and simulations.

RESULTS

The final model is a two-compartment model that includes the effects of body weight using allometric scaling with fixed exponents and maturation of clearance. For a typical subject, scaled to the adult body weight of 70 kg, population pharmacokinetic values were estimated at 8.52 L/h for clearance (when maturation function was 1), 25.5 L/h for intercompartmental clearance, and 5.71 L and 39.8 L for the volume of the central and peripheral compartment, respectively. Based on the final model, maturation reaches 50% of the adult clearance in 45.9 weeks of postmenstrual age. The influence of gender, ABCB1 genotype and biochemical parameters on midazolam clearance was not detected. Results of simulations indicate the need for reduced dosing in certain groups of patients in order to maintain plasma concentrations of midazolam within recommended values.

CONCLUSIONS

The developed population pharmacokinetic model can contribute to the dosing optimisation of midazolam, especially in critically ill children as it includes the influence of size and maturation of clearance, which are important parameters for achieving the desired plasma concentrations of midazolam.

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.

Linking the Epigenome with Exposure Effects and Susceptibility: The Epigenetic Seed and Soil Model

The epigenome is a dynamic mediator of gene expression that shapes the way that cells, tissues, and organisms respond to their environment. Initial studies in the emerging field of "toxicoepigenetics" have described either the impact of an environmental exposure on the epigenome or the association of epigenetic signatures with the onset or progression of disease; however, the majority of these pioneering studies examined the relationship between discrete epigenetic modifications and the effects of a single environmental factor. Although these data provide critical blocks with which we construct our understanding of the role of the epigenome in susceptibility and disease, they are akin to individual letters in a complex alphabet that is used to compose the language of the epigenome. Advancing the use of epigenetic data to gain a more comprehensive understanding of the mechanisms underlying exposure effects, identify susceptible populations, and inform the next generation risk assessment depends on our ability to integrate these data in a way that accounts for their cumulative impact on gene regulation. Here we will review current examples demonstrating associations between the epigenetic impacts of intrinsic factors, such as such as age, genetics, and sex, and environmental exposures shape the epigenome and susceptibility to exposure effects and disease. We will also demonstrate how the "epigenetic seed and soil" model can be used as a conceptual framework to explain how epigenetic states are shaped by the cumulative impacts of intrinsic and extrinsic factors and how these in turn determine how an individual responds to subsequent exposure to environmental stressors.

Clinical Pharmacology Studies in Critically Ill Children

Developmental and physiological changes in children contribute to variation in drug disposition with age. Additionally, critically ill children suffer from various life-threatening conditions that can lead to pathophysiological alterations that further affect pharmacokinetics (PK). Some factors that can alter PK in this patient population include variability in tissue distribution caused by protein binding changes and fluid shifts, altered drug elimination due to organ dysfunction, and use of medical interventions that can affect drug disposition (e.g., extracorporeal membrane oxygenation and continuous renal replacement therapy). Performing clinical studies in critically ill children is challenging because there is large inter-subject variability in the severity and time course of organ dysfunction; some critical illnesses are rare, which can affect subject enrollment; and critically ill children usually have multiple organ failure, necessitating careful selection of a study design. As a result, drug dosing in critically ill children is often based on extrapolations from adults or non-critically ill children. Dedicated clinical studies in critically ill children are urgently needed to identify optimal dosing of drugs in this vulnerable population. This review will summarize the effect of critical illness on pediatric PK, the challenges associated with performing studies in this vulnerable subpopulation, and the clinical PK studies performed to date for commonly used drugs.

Inter-individual variation in midazolam clearance in children

OBJECTIVES

To determine the extent of inter-individual variation in clearance of midazolam in children and establish which factors are responsible for this variation.

METHODS

A systematic literature review was performed to identify papers describing the clearance of midazolam in children. The following databases were searched: Medline, Embase, International Pharmaceutical Abstracts, CINAHL and Cochrane Library. From the papers, the range in plasma clearance and the coefficient of variation (CV) in plasma clearance were determined.

RESULTS

25 articles were identified. Only 13 studies gave the full range of clearance values for individual patients. The CV was greater in critically ill patients (18%-170%) than non-critically ill patients (13%-54%). Inter-individual variation was a major problem in all age groups of critically ill patients. The CV was 72%-106% in preterm neonates, 18%-73% in term neonates, 31%-130% in infants, 21%-170% in children and 47%-150% in adolescents. The mean clearance was higher in children (1.1-16.7 mL/min/kg) than in neonates (0.78-2.5 mL/min/kg).

CONCLUSIONS

Large inter-individual variation was seen in midazolam clearance values in critically ill neonates, infants, children and adolescents.

Clinical pharmacology of midazolam in neonates and children: effect of disease-a review

Midazolam is a benzodiazepine with rapid onset of action and short duration of effect. In healthy neonates the half-life (t_1/2) and the clearance (Cl) are 3.3-fold longer and 3.7-fold smaller, respectively, than in adults. The volume of distribution (Vd) is 1.1 L/kg both in neonates and adults. Midazolam is hydroxylated by CYP3A4 and CYP3A5; the activities of these enzymes surge in the liver in the first weeks of life and thus the metabolic rate of midazolam is lower in neonates than in adults. Midazolam acts as a sedative, as an antiepileptic, for those infants who are refractory to standard antiepileptic therapy, and as an anaesthetic. Information of midazolam as an anaesthetic in infants are very little. Midazolam is usually administered intravenously; when minimal sedation is required, intranasal administration of midazolam is employed. Disease affects the pharmacokinetics of midazolam in neonates; multiple organ failure reduces the Cl of midazolam and mechanical ventilation prolongs the t_1/2 of this drug. ECMO therapy increases t_1/2, Cl, and Vd of midazolam several times. The adverse effects of midazolam in neonates are scarce: pain, tenderness, and thrombophlebitis may occur. Respiratory depression and hypotension appear in a limited percentage of infants following intravenous infusion of midazolam. In conclusion, midazolam is a safe and effective drug which is employed as a sedative, as antiepileptic agent, for infants who are refractory to standard antiepileptic therapy, and as an anaesthetic.

Randomized controlled trial of daily interruption of sedatives in critically ill children

AIM

To study the feasibility of daily interruption of sedatives in critically ill children.

METHODS

Prospective randomized controlled open-label trial, performed in a pediatric intensive care unit of a tertiary care teaching and referring hospital. 30 children (0-12 years) receiving mechanically ventilation for >24 h were included. In the intervention group, all sedatives were stopped daily and restarted when COMFORT-behavior score ≥17. The control group received standard care. Primary end points were amounts of sedatives and number of bolus medications in the first 3 days after enrollment and number of (near) incidents. Secondary end points were duration of mechanical ventilation, length of stay in pediatric intensive care, and changes in COMFORT-behavior score.

RESULTS

Midazolam and morphine use were lower in the intervention group compared with the control group (P = 0.007 and P = 0.02, respectively), whereas the number of bolus medications did not differ between groups. Two complications were recorded: one patient (intervention group) lost his intravenous line, and one patient (control group) had an unplanned extubation. Duration of mechanical ventilation was significantly shorter in the intervention group compared with the control group (median [interquartile range] of 4 [3-8] and 9 [4-10] days, respectively, P = 0.03). Length of stay in the PICU in the intervention group was significantly shorter than in the control group (median [interquartile range] of 6 [4-9] and 10 [7-15] days, respectively, P = 0.01).

CONCLUSIONS

Daily interruption of sedatives in critically ill children is feasible, results in decreased use of sedation, earlier extubation, and shorter length of stay.

Assessing circadian rhythms during prolonged midazolam infusion in the pediatric intensive care unit (PICU) children

BACKGROUND

This study evaluates possible circadian rhythms during prolonged midazolam infusion in 27 pediatric intensive care unit (PICU) children under mechanical ventilation.

METHODS

Blood samples for midazolam and 1-OH-midazolam assay were collected throughout the infusion at different times of the day. The blood pressure, heart rate and body temperature were recorded every hour for the rhythms analysis. Population nonlinear mixed-effect modeling with NONMEM was used for data analysis.

RESULTS

A two-compartment model for midazolam pharmacokinetics and a one-compartment model for midazolam metabolite adequately described the data. The 24 h profiles of all monitored physiological parameters were greatly disturbed/abolished in comparison with the well-known 24 h rhythmic patterns in healthy subjects. There was no significant circadian rhythm detected with respect to midazolam pharmacokinetics, its active metabolite pharmacokinetics and all monitored parameters.

CONCLUSIONS

We concluded that the light-dark cycle did not influence midazolam pharmacokinetics in intensive care units children. Also, endogenous rhythms in critically ill and sedated children are severely disturbed and desynchronized. Our results confirmed that it is necessary to adjust the dose of midazolam to the patient's body weight. The low value of midazolam clearances observed in our study was probably caused by mechanical ventilation, which was shown to decrease the cardiac output.

Critical illness is a major determinant of midazolam clearance in children aged 1 month to 17 years

BACKGROUND

In children, a large variability in pharmacokinetics of midazolam, a cytochrome P450 3A4/5 (CYP3A4/5) enzyme substrate, has been described, which cannot be explained by age-related changes alone. In this study, these age-related changes are studied in relation to other covariates to explain the variability in the pharmacokinetics of midazolam in children.

METHODS

Population pharmacokinetic modeling was performed using a joint dataset of 3 studies conducted previously: study 1: pediatric intensive care patients requiring sedation in the intensive care unit; study 2: pediatric oncology patients undergoing an invasive procedure; study 3: otherwise healthy infants admitted for postoperative monitoring after elective major craniofacial surgery. Midazolam, 1-hydroxymidazolam, and 1-hydroxymidazolam glucuronide concentrations were considered to determine the pharmacokinetics of midazolam and metabolites using NONMEM 6.2. SimCYP pediatric simulator was used for simulation.

RESULTS

Fifty-four children aged between 1 month and 17 years who received intravenous midazolam (bolus and/or continuous infusion) for sedation were included in this study. A reduction of 93% for CYP3A4/5 (midazolam to 1-hydroxymidazolam) and 86% for uridine diphosphate glucuronosyltransferase (1-hydroxymidazolam to 1-hydroxymidazolam glucuronide) mediated clearance was found in pediatric intensive care patients compared with the other 2 patient groups. We did not find a significant influence of age or bodyweight on CYP3A4/5-mediated total clearance. For uridine diphosphate glucuronosyltransferase-mediated clearance, bodyweight explained 41.5% of the variability.

CONCLUSIONS

From infancy to adolescence, critical illness seems to be a major determinant of midazolam clearance, which may result from reduced CYP3A4/5 activity due to inflammation. This may have important implications for dosing of midazolam and other CYP3A drug substrates in critically ill children.

Ontogeny and sorafenib metabolism

PURPOSE

To investigate the role of ontogeny in sorafenib metabolism to the equipotent active metabolite sorafenib N-oxide.

EXPERIMENTAL DESIGN

Steady-state pharmacokinetic studies of sorafenib and metabolites were conducted in 30 children and young adults (17 males; median age, 9.5 years) receiving sorafenib 150 mg/m(2) or 200 mg/m(2) twice daily. Sorafenib metabolism was evaluated in vitro at 10 μmol/L using a panel of purified human cytochrome P450 (CYP) enzymes. Sorafenib metabolism and CYP3A4 expression was evaluated in 52 human liver samples from donors of ≤20 years old. The drug-drug interaction potential between sorafenib and azole antifungal agents was evaluated in vitro and in vivo.

RESULTS

No age-related differences in sorafenib apparent oral clearance were observed. Mean sorafenib N-oxide metabolite ratio was 0.27 ± 0.14. In children of ≤10 years of age, boys had approximately 2-fold higher N-oxide ratios than girls (0.40 ± 0.15 vs. 0.22 ± 0.12, P = 0.026). Of the CYPs evaluated, sorafenib was exclusively metabolized to sorafenib N-oxide by CYP3A4. A trend for increased N-oxide formation in boys was observed in liver samples, which correlated with CYP3A4 mRNA expression. Posaconazole and voriconazole potently inhibited sorafenib N-oxide formation in vitro, and reduced sorafenib N-oxide formation in 3 children given sorafenib concurrent with azoles.

CONCLUSION

We have identified several factors affecting interpatient variability in sorafenib metabolism to the active N-oxide metabolite including age, sex, and concurrent treatment with azole antifungals. This knowledge may provide important considerations for the clinical use of sorafenib in children and possibly other kinase inhibitors undergoing CYP3A4-mediated metabolism.

A maturation model for midazolam clearance

BACKGROUND

Physiological-based pharmacokinetic models have been used to describe midazolam clearance (CL) maturation. There are no maturation descriptors of CL from neonate to adulthood based on reported estimates at different ages.

METHODS

Published CL estimates after intravenous administration from time-concentration profiles were used to construct a maturation model based on size and age. Curve fitting was performed using nonlinear mixed effects models.

RESULTS

There were 16 publications reporting an estimate of CL after intravenous administration in children, although few estimates were available from 44-80 weeks postmenstrual age (PMA). CL maturation, standardized to a 70 -kg person was described using the Hill equation. Mature CL was 523 (CV 32%, 95%CI 469, 597) ml·min(-1) ·70 kg(-1) . The maturation half-time was 73.6 (95%CI 59.4, 80.0) weeks PMA and the Hill coefficient 3 (95%CI 2.2, 4.1). Predicted CL changes with age based on this model were in close agreement with physiologically based pharmacokinetic (PBPK) models. A comparison with a published PBPK model predictions revealed a root mean squared prediction error (precision) of 4.0% (95%CI 1.1, 5.8) and bias was -0.9% (95%CI -4.3, 2.6).

CONCLUSIONS

Previously published pharmacokinetic parameters can be used to develop maturation models that address gaps in current knowledge regarding the influence of age on a drug's disposition. If a midazolam sedation target concentration of 0.1 mg·l(-1) , similar to that given to adults, is assumed, then we might anticipate steady-state infusion rates of 0.014 mg·kg(-1) ·h(-1) in neonates, 0.05 mg·kg(-1) ·h(-1) in a 1-year-old, 0.06 mg·kg(-1) ·h(-1) in a 5-year-old and 0.05 mg·kg(-1) ·h(-1) in a 12-year-old child. Age-related pharmacodynamic differences that will affect dose and the impact of active metabolites on response are not yet quantified.

Efficacy of sedation regimens to facilitate mechanical ventilation in the pediatric intensive care unit: a systematic review

OBJECTIVE

Children admitted to pediatric intensive care units (PICUs) often receive sedatives to facilitate mechanical ventilation. However, despite their widespread use, data supporting appropriate dosing, safety, and optimal regimens for sedation during mechanical ventilation are lacking. Therefore, we conducted a systematic review of published data regarding efficacy of sedation to facilitate mechanical ventilation in PICU patients. Our primary objective was to identify and evaluate the quality of evidence supporting sedatives used in PICUs for this purpose.

DATA SOURCES

We searched MEDLINE, EMBASE, and The Cochrane Registry of Clinical Trials from 1966 to June 2008 to identify published articles evaluating sedation regimens to facilitate mechanical ventilation in PICU patients.

STUDY SELECTION

We included only those studies of intubated PICU or pediatric cardiac intensive care unit patients receiving pharmacologic agents to facilitate mechanical ventilation that reported quality of sedation as an outcome.

DATA EXTRACTION

We analyzed studies separately for study type and by agents being studied. Studies were appraised using criteria of particular importance for reviews evaluating sedatives.

DATA SYNTHESIS

Our search strategy yielded 39 studies, including 3 randomized trials, 15 cohort studies, and 21 cases series or reports. The 39 studies evaluated a total of 39 different sedation regimens, with 21 different scoring systems, in a total of 901 PICU/cardiac intensive care unit patients ranging in age from 3 days to 19 years old. Most of the studies were small (<30 patients), and only four studies compared one or more agents to another. Few studies thoroughly evaluated drug safety, and only one study met all quality criteria.

CONCLUSIONS

Despite the widespread use of sedatives to facilitate mechanical ventilation in the PICU, we found that high-quality evidence to guide clinical practice is still limited. Pediatric randomized, controlled trials with reproducible methods and assessment of drug safety are needed.

Intestinal metabolism and transport of drugs in children: the effects of age and disease

The presence of cytochrome P450 enzymes in the small bowel results in the reduced bioavailability of several drugs. Recently, there has been much research on the interplay between these enzymes and transporter proteins such as P-glycoprotein. Intestinal drug metabolism not only has an effect on drug disposition but also may have a role in protecting the host from xenobiotics. Although there is some information on how both the enzymes and transporters develop in the small bowel with age, there is little information regarding the clinical effects of these changes. In addition to developmental changes, the influence of gastrointestinal disease and nutrition are additional covariates in the intestinal metabolism of drugs.

Pharmacokinetics and clinical efficacy of midazolam in children with severe malaria and convulsions

AIM

To investigate the pharmacokinetics and clinical efficacy of intravenous (IV), intramuscular (IM) and buccal midazolam (MDZ) in children with severe falciparum malaria and convulsions.

METHODS

Thirty-three children with severe malaria and convulsions lasting ≥5 min were given a single dose of MDZ (0.3 mg kg⁻¹) IV (n = 13), IM (n = 12) or via the buccal route (n = 8). Blood samples were collected over 6 h post-dose for determination of plasma MDZ and 1′-hydroxymidazolam concentrations. Plasma concentration–time data were fitted using pharmacokinetic models.

RESULTS

Median (range) MDZ C_max of 481 (258–616), 253 (96–696) and 186 (64–394) ng ml⁻¹ were attained within a median (range) t_max of 10 (5–15), 15 (5–60) and 10 (5–40) min, following IV, IM and buccal administration, respectively. Mean (95% confidence interval) of the pharmacokinetic parameters were: AUC(0,∞) 596 (327, 865), 608 (353, 864) and 518 (294, 741) ng ml⁻¹ h; V_d 0.85 l kg⁻¹; clearance 14.4 ml min⁻¹ kg⁻¹, elimination half-life 1.22 (0.65, 1.8) h, respectively. A single dose of MDZ terminated convulsions in all (100%), 9/12 (75%) and 5/8 (63%) children following IV, IM and buccal administration. Four children (one in the IV, one in the IM and two in the buccal groups) had respiratory depression.

CONCLUSIONS

Administration of MDZ at the currently recommended dose resulted in rapid achievement of therapeutic MDZ concentrations. Although IM and buccal administration of MDZ may be more practical in peripheral healthcare facilities, the efficacy appears to be poorer at the dose used, and a different dosage regimen might improve the efficacy.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Midazolam (MDZ), a water-soluble benzodiazepine, can be administered via several routes, including intravenously (IV), intramuscularly (IM) and buccal routes to terminate convulsions. It may be a suitable alternative to diazepam to stop convulsions in children with severe malaria, especially at peripheral healthcare facilities. The pharmacokinetics of MDZ have not been described in African children, in whom factors such as the aetiology and nutritional status may influence the pharmacokinetics.

WHAT THIS STUDY ADDS

Administration of MDZ (IV, IM, or buccal) at the currently recommended dose (0.3 mg kg⁻¹) resulted in rapid achievement of median maximum plasma concentrations of MDZ within the range 64–616 ng ml⁻¹, with few clinically significant cardio-respiratory effects. A single dose of MDZ rapidly terminated (within 10 min) seizures in all (100%), 9/12 (75%) and 5/8 (63%) children following IV, IM and buccal administration, respectively. Although IM and buccal MDZ may be the preferred treatment for children in the pre-hospital settings the efficacy appears to be poorer.

New perspectives on the impact of cytochrome P450 3A expression for pediatric pharmacology

Advances in the basic and clinical sciences of drug actions and safety have been applied almost exclusively to the largest demographic patient group--adults. Metabolism-dependent drug clearance is not only a primary determinant for obtaining efficacious drug exposure, but could also demonstrate clear age-dependence. These concepts are exemplified by the three major human cytochrome P450 (CYP) 3A enzymes: CYP3A4, CYP3A5 and CYP3A7. Recent preclinical and clinical studies show CYP3A7 is the most abundant CYP3A enzyme in fetal liver, with a gradual shift towards CYP3A4 expression throughout childhood. However, the polymorphic nature and regulatory intricacies of CYP3A5 and CYP3A7 expression could cause an underappreciated contribution to interindividual variability in drug response and safety.

Population pharmacokinetics and metabolism of midazolam in pediatric intensive care patients

OBJECTIVE

To determine the pharmacokinetics and metabolism of midazolam in pediatric intensive care patients.

DESIGN

Prospective population pharmacokinetic study.

SETTING

Pediatric intensive care unit.

PATIENTS

Twenty-one pediatric intensive care patients aged between 2 days and 17 yrs.

INTERVENTIONS

The pharmacokinetics of midazolam and metabolites were determined during and after a continuous infusion of midazolam (0.05-0.4 mg/kg/hr) for 3.8 hrs to 25 days administered for conscious sedation.

MEASUREMENTS AND MAIN RESULTS

Blood samples were taken at different times during and after midazolam infusion for determination of midazolam, 1-OH-midazolam, and 1-OH-midazolam-glucuronide concentrations via high-performance liquid chromatography-ultraviolet detection. A population analysis was conducted via a two-compartment pharmacokinetic model by the NPEM program. The final population model was used to generate individual Bayesian posterior pharmacokinetic parameter estimates. Total body clearance, apparent volume distribution in terminal phase, and plasma elimination half-life were (mean +/- sd, n = 18): 5.0 +/- 3.9 mL/kg/min, 1.7 +/- 1.1 L/kg, and 5.5 +/- 3.5 hrs, respectively. The mean 1-OH-midazolam/midazolam ratio and (1-OH-midazolam + 1-OH-midazolam-glucuronide)/midazolam ratio were 0.14 +/- 0.21 and 1.4 +/- 1.1, respectively. Data from three patients with renal failure, hepatic failure, and concomitant erythromycin-fentanyl therapy were excluded from the final pharmacokinetic analysis.

CONCLUSIONS

We describe population and individual midazolam pharmacokinetic parameter estimates in pediatric intensive care patients by using a population modeling approach. Lower midazolam elimination was observed in comparison to other studies in pediatric intensive care patients, probably as a result of differences in study design and patient differences such as age and disease state. Covariates such as renal failure, hepatic failure, and concomitant administration of CYP3A inhibitors are important predictors of altered midazolam and metabolite pharmacokinetics in pediatric intensive care patients. The derived population model can be useful for future dose optimization and Bayesian individualization.

[Sedation induced by midazolam in intensive care: pharmacologic and pharmacokinetic aspects]

OBJECTIVE

Review on midazolam in order to optimize drug utilisation and therapeutic monitoring.

DATA SOURCES

Research of English or French articles published until August 2001, using Medline database. The key words were: midazolam, pharmacokinetics, pharmacodynamic, sedation, drug interaction.

STUDY SELECTION

Original articles, clinical cases and letters to the Editor were selected. Animal studies were excluded.

DATA EXTRACTION

The articles were analysed according to their interest in midazolam clinical practice.

DATA SYNTHESIS

Midazolam is a benzodiazepine widely used in intensive care unit, as a sedative, anxiety-relieving, and amnesic drug. Midazolam could be used in patients with cardiac, or respiratory failure, and in neurosurgery. A great interindividual variability on pharmacokinetic and pharmacodynamic response was observed. In intensive care patients, elimination half-life is known to be widely increased. Midazolam is metabolised by hepatic microsomes. The major metabolite is the 1-hydroxymidazolam, which is pharmacologically active. A prolonged sedation due to an accumulation of conjugated metabolite was observed in renal failure patients. Enzymatic inductors or inhibitors could influence pharmacokinetics and pharmacodynamic effects of midazolam.

CONCLUSION

According to midazolam pharmacokinetic and pharmacodynamic variability, an individual dosage adjustment is essential for long-term sedation. Target controlled sedation could be a mean to limit the variability and to reach quickly the pharmacodynamic effect.

The single-dose pharmacokinetics of midazolam and its primary metabolite in pediatric patients after oral and intravenous administration

The first-dose pharmacokinetics of midazolam and its primary alpha-hydroxymetabolite were studied after single-dose administration. Eligible study patients were enrolled into one of three study arms: Arm I (midazolam/metabolite pharmacokinetic evaluation after oral administration of a syrup formulation), Arm II (the absolute bioavailability of midazolam syrup), and Arm III (midazolam and metabolite pharmacokinetics after IV administration). Complete blood sampling for pharmacokinetic analysis was available in 87 subjects. Midazolam absorption after administration of the oral syrupformulation was rapid, with adolescents absorbing the drug at approximately half the rate observed in younger children (ages 2 to < 12 years). Furthermore, midazolam t 1/2 was prolonged and CL/F reducedin adolescents as compared with younger children. Although the midazolam Vd/F appeared larger in the youngest age group after oral administration, this observation was not apparent after IV dosing, suggesting subject differences in bioavailability rather than distribution. Like midazolam, the disposition characteristics for a-hydroxymidazolam were also highly variable, with the greatest formation of metabolite (reflected by the AUC ratio) observed in children ages 2 to < 12 years. The A UC ratios of alpha-hydroxymidazolam to midazolam after IV dosing were similar across all age groups and were smaller than corresponding values following oral administration. The absolute bioavailability of midazolam averaged 36% with a very broad range (9%-71%). No relationship between midazolam bioavailability and age was observed. Overall, the disposition characteristics of midazolam and its a-hydroxy metabolite were highly variable, appeared independent of age and dose administered, and were linear over the dose range studied (0.25 to 1 mg/kg). These data suggest that an initial oral dose of 0.2 to 0.3 mg/kg should be adequateforsuccessful sedation of most pediatric patients. The inherent variability in midazolam bioavailability and metabolism underscores the importance of titrating midazolam dose to desired effect.

Parental perceptions of comfort during mechanical ventilation

There are no reports of the parental perceptions of comfort during the mechanical ventilation of children. We have assessed the quality of sedation in 28 mechanically ventilated children and compared these results to an overall parental assessment of comfort, obtained by postal questionnaire. There was no correlation between the parental assessment of comfort and the paediatric intensive care unit (PICU) staff satisfaction with the level of sedation. Parental assessment of comfort was positively correlated with the duration of ventilation, whilst PICU staff satisfaction was positively correlated with the age of the child. Parents appear to become more satisfied with the degree of comfort of their children as the duration of mechanical ventilation increases, which is an effect that may have an important bearing on communication between parents and health professionals. Our results also suggest that the commonly used sedation regime of midazolam and morphine is less effective in younger children.

A comparison of the ontogeny of enterocytic and hepatic cytochromes P450 3A in the rat

Enzymes of the cytochrome P450 3A (CYP3A) sub-family are abundant in adult liver and gut and contribute significantly to the first-pass metabolism of many orally administered drugs. The development of CYP3A enzymes with regard to their expression and activity in enterocytic and hepatic microsomes from 1-day-old through to adult male and female rats has been studied. Microsomes were prepared by calcium precipitation. Enzyme expression was assessed semi-quantitatively by Western blotting using rat polyclonal CYP3A2 and 2C11 antibodies and peptide antibodies specific to rat CYPs 3A1, 3A2, 2C12, and 2C13. The formation of 6beta-hydroxytestosterone (6OHT), determined by HPLC, was used as a measure of enzyme activity. Formation of 6OHT by enterocytic microsomes was similar for males and females and showed a sharp increase at weaning. This pattern was mirrored by levels of immunoquantifiable CYP3A2 (CYP3A9), but CYP3A1 followed a more gradual development. CYPs 2C11, 2C12, or 2C13 were not detected in gut microsomes. In contrast, CYPs 3A1, 3A2, 2C11, 2C12, and 2C13 were all expressed in hepatic microsomes. There was no surge in hepatic enzyme expression or hepatic 6OHT formation at weaning, and a marked sex difference in 6OHT formation was apparent from day 25. The surge in gut activity at weaning may be a protective mechanism against ingested toxins.

Recollection of children following intensive care

BACKGROUND AND AIMS

The recollections of critically ill children following discharge from the paediatric intensive care unit (PICU) have not previously been described. We have interviewed such children to establish the nature of their recollections.

METHODS

Children aged 4 years and above were interviewed following discharge from the PICU at the Queens Medical Centre, Nottingham, either in hospital or at home, using a semistructured interview. Their recollections were recorded and interpreted by content analysis.

RESULTS

A total of 38 interviews were carried out; 44 specific recollections were reported, the majority being neutral (60%) or positive (25%). Only 15% of recollections were negative. Negative recollections related to aspects of medical care and environmental factors. No child treated with neuromuscular blocking agents remembered any period of therapeutic paralysis.

CONCLUSIONS

Children's recollections of PICU are mainly neutral or positive. Mechanically ventilated children sedated with midazolam and morphine remember little of endotracheal intubation.

Pharmacokinetics of midazolam in critically ill pediatric patients

Midazolam is frequently used to produce sedation in critically ill pediatric patients. We studied the pharmacokinetics of midazolam in 22 patients (age 8 days to 16 years). The intravenous infusion rate to produce sedation ranged from 49-385 mcg/kg/hr. The blood samples were obtained at steady-state and midazolam was measured by gas chromatography with electron capture. The steady-state plasma concentrations of midazolam ranged from 49-385 ng/mL. The total clearance, apparent volume of distribution, and elimination half-life ranged from 0.1-3.1 L/kg/hr, 0.2-3.5 L/kg, and 0.3-10.9 hours, respectively. The marked interpatient variability in pharmacokinetics explains in part, the substantial variation in dosage requirements of midazolam to produce sedation in critically ill pediatric patients.

Cytochrome P450 3A: ontogeny and drug disposition

The maturation of organ systems during fetal life and childhood exerts a profound effect on drug disposition. The maturation of drug-metabolising enzymes is probably the predominant factor accounting for age-associated changes in non-renal drug clearance. The group of drug-metabolising enzymes most studied are the cytochrome P450 (CYP) superfamily. The CYP3A subfamily is the most abundant group of CYP enzymes in the liver and consists of at least 3 isoforms: CYP3A4, 3A5 and 3A7. Many drugs are mainly metabolised by the CYP3A subfamily. Therefore, maturational changes in CYP3A ontogeny may impact on the clinical pharmacokinetics of these drugs. CYP3A4 is the most abundantly expressed CYP and accounts for approximately 30 to 40% of the total CYPcontent in human adult liver and small intestine. CYP3A5 is 83% homologous to CYP3A4, is expressed at a much lower level than CYP3A4 in the liver, but is the main CYP3A isoform in the kidney. CYP3A7 is the major CYP isoform detected in human embryonic, fetal and newborn liver, but is also detected in adult liver, although at a much lower level than CYP3A4. Substrate specificity for the individual isoforms has not been fully elucidated. Because of large interindividual differences in CYP3A4 and 3A5 expression and activity, genetic polymorphisms have been suggested. However, although some gene mutations have been identified, the impact of these mutations on the pharmacokinetics of CYP3A substrates has to be established. Ontogeny of CYP3A activity has been studied in vitro and in vivo. CYP3A7 activity is high during embryonic and fetal life and decreases rapidly during the first week of life. Conversely, CYP3A4 is very low before birth but increases rapidly thereafter, reaching 50% of adult levels between 6 and 12 months of age. During infancy, CYP3A4 activity appears to be slightly higher than that of adults. Large interindividual variations in CYP3A5 expression and activity were observed during all stages of development, but no apparent developmental pattern of CYP3A5 activity has been identified to date. Profound changes occur in the activity of CYP3A isoforms during all stages of development. These changes have, in many instances, proven to be of clinical significance when treatment involves drugs that are substrates, inhibitors or inducers of CYP3A. Investigators and clinicians should consider the impact of ontogeny on CYP3A in both pharmacokinetic study design and data interpretation, as well as when prescribing drugs to children.

Clinical pharmacology of midazolam in infants and children

Midazolam is a parenteral benzodiazepine with sedative, amnesic, anxiolytic, muscle relaxant and anticonvulsant properties. The drug exerts its clinical effect by binding to a receptor complex which facilitates the action of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). Midazolam has a faster onset and shorter duration of action than other benzodiazepines such as diazepam and lorazepam. The most serious adverse events associated with midazolam in children include hypoventilation, decreased oxygen saturation, apnoea and hypotension. It is water soluble in the commercially prepared formulation but becomes lipid soluble at physiological pH and can then cross the blood brain barrier. It is metabolised in the liver by the cytochrome P450 system, and its chief metabolite is 1-hydroxymethyl midazolam. The latter is conjugated to the glucuronide form, and it has only minimal biological activity. Midazolam is excreted primarily by the kidney. Its half-life in children over 12 months is reported to be 0.8 to 1.8 hours, with a clearance of 4.7 to 19.7 ml/min/kg. Doses given to children must be calculated on a mg/kg basis. For children 6 months to 5 years of age the initial dose is 0.05 to 0.1 mg/kg. A total dose up to 0.6 mg/kg titrated slowly may be necessary to achieve the desired endpoint. For children 6 to 12 years of age the initial dose is 0.025 to 0.05 mg/kg with a total dose up to 0.4 mg/kg to achieve the desired end-point.