Serum gentamicin concentrations in encephalopathic infants are not affected by therapeutic hypothermia

Drug Disposition in Neonatal Göttingen Minipigs: Exploring Effects of Perinatal Asphyxia and Therapeutic Hypothermia

Asphyxiated neonates often undergo therapeutic hypothermia (TH) to reduce morbidity and mortality. Since both perinatal asphyxia (PA) and TH influence physiology, altered pharmacokinetics (PK) and pharmacodynamics (PD) are expected. Given that TH is the standard of care for PA with moderate to severe hypoxic-ischemic encephalopathy, disentangling the effect of PA versus TH on PK/PD is not possible in clinical settings. However, animal models can provide insights into this matter. The (neonatal) Göttingen Minipig, the recommended strain for nonclinical drug development, was selected as translational model. Four drugs-midazolam (MDZ), fentanyl (FNT), phenobarbital (PHB), and topiramate (TPM)-were intravenously administered under four conditions: control (C), therapeutic hypothermia (TH), hypoxia (H), and hypoxia plus TH (H+TH). Each group included six healthy male neonatal Göttingen Minipigs anesthetized for 24 hours. Blood samples were drawn at 0 (predose) and 0.5, 2, 2.5, 3, 4, 4.5, 6, 8, 12, and 24 hours post drug administration. Drug plasma concentrations were determined using validated bioanalytical assays. The PK parameters were estimated through compartmental and noncompartmental PK analysis. The study showed a statistically significant decrease in FNT clearance (CL; 66% decrease), with an approximately threefold longer half-life (t1/2) in the TH group. The H+TH group showed a 17% reduction in FNT CL, with a 62% longer t1/2 compared with the C group; however, it was not statistically significant. Although not statistically significant, trends toward lower CL and longer t1/2 were observed in the TH and H+TH groups for MDZ and PHB. Additionally, TPM demonstrated a 28% decrease in CL in the H group compared with controls. SIGNIFICANCE STATEMENT: The overarching goal of this study using the neonatal Göttingen Minipig model was to disentangle the effects of systemic hypoxia and TH on PK using four model drugs. Such insights can subsequently be used to inform and develop a physiologically based pharmacokinetic model, which is useful for drug exposure prediction in human neonates.

Pharmacometric approach to assist dosage regimen design in neonates undergoing therapeutic hypothermia

BACKGROUND

Therapeutic hypothermia (TH) is the treatment of choice for neonates diagnosed with perinatal asphyxia (PA). Dosing recommendations of various therapeutic agents including antimicrobials were not specifically available for the neonates undergoing TH.

METHODS

A systematic search methodology was used to identify pharmacokinetic (PK) studies of antimicrobials during TH. Antimicrobials with multiple PK studies were identified to create a generalizable PK model. Pharmacometric simulations were performed using the PUMAS software platform to reproduce the results of published studies. A suitable model that could reproduce the results of all other published studies was identified. With the help of a generalizable model, an optimal dosage regimen was designed considering the important covariates of the identified model.

RESULTS

With the systematic search, only gentamicin had multiple PK reports during TH. A generalizable model was identified and the model predictions could match the reported/observed concentrations of publications. Birth weight and serum creatinine were the significant covariates influencing the PK of gentamicin in neonates. A dosage nomogram was designed using pharmacometric simulations to maintain gentamicin concentrations below 10 μg/mL at peak and below 2 μg/mL at trough.

CONCLUSIONS

A generalizable PK model for gentamicin during TH in neonates was identified. Using the model, a dosing nomogram for gentamicin was designed.

IMPACT

Dosing guidelines for antimicrobials during TH in neonates is lacking. This is the first study to identify the generalizable model for gentamicin during TH in neonates. Nomogram, proposed in the study, will aid the clinicians to individualize gentamicin dosing regimen for neonates considering the birth weight and serum creatinine.

Pharmacokinetics of Antibiotics in Pediatric Intensive Care: Fostering Variability to Attain Precision Medicine

Children show important developmental and maturational changes, which may contribute greatly to pharmacokinetic (PK) variability observed in pediatric patients. These PK alterations are further enhanced by disease-related, non-maturational factors. Specific to the intensive care setting, such factors include critical illness, inflammatory status, augmented renal clearance (ARC), as well as therapeutic interventions (e.g., extracorporeal organ support systems or whole-body hypothermia [WBH]). This narrative review illustrates the relevance of both maturational and non-maturational changes in absorption, distribution, metabolism, and excretion (ADME) applied to antibiotics. It hereby provides a focused assessment of the available literature on the impact of critical illness—in general, and in specific subpopulations (ARC, extracorporeal organ support systems, WBH)—on PK and potential underexposure in children and neonates. Overall, literature discussing antibiotic PK alterations in pediatric intensive care is scarce. Most studies describe antibiotics commonly monitored in clinical practice such as vancomycin and aminoglycosides. Because of the large PK variability, therapeutic drug monitoring, further extended to other antibiotics, and integration of model-informed precision dosing in clinical practice are suggested to optimise antibiotic dose and exposure in each newborn, infant, or child during intensive care.

Glomerular Filtration Rate in Asphyxiated Neonates Under Therapeutic Whole-Body Hypothermia, Quantified by Mannitol Clearance

BACKGROUND

Therapeutic hypothermia (TH) is an established intervention to improve the outcome of neonates with moderate-to-severe hypoxic-ischemic encephalopathy resulting from perinatal asphyxia. Despite this beneficial effect, TH may further affect drug elimination pathways such as the glomerular filtration rate.

OBJECTIVES

The objective of this study was to quantify the effect of TH in addition to asphyxia on mannitol clearance as a surrogate for the glomerular filtration rate.

METHODS

The effect of asphyxia and TH (mild vs moderate/severe) on mannitol clearance was assessed using a population approach, based on mannitol observations collected in the ALBINO (ALlopurinol in addition to TH for hypoxic-ischemic Brain Injury on Neurocognitive Outcome) trial, as some were exposed to a second dose of 10 mg/kg intravenous mannitol as placebo to ensure blinding. Pharmacokinetic analysis and model development were conducted using NONMEM version 7.4.

RESULTS

Based on 77 observations from 17 neonates (TH = 13), a one-compartment model with first-order linear elimination best described the observed data. To account for prenatal glomerular filtration rate maturation, both birthweight and gestational age were implemented as clearance covariates using an earlier published three-quarters power function and a sigmoid hyperbolic function. Our final model predicted a mannitol clearance of 0.15 L/h for a typical asphyxia neonate (39.5 weeks, birthweight 3.25 kg, no TH), lower than the reported value of 0.33 L/h for a healthy neonate of similar age and weight. By introducing TH as a binary covariate on clearance, the additional impact of TH on mannitol clearance was quantified (60% decrease).

CONCLUSIONS

Mannitol clearance was decreased by approximately 60% in neonates undergoing TH, although this is likely confounded with asphyxia severity.

TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT03162653.

Pharmacokinetics during therapeutic hypothermia for neonatal hypoxic ischaemic encephalopathy: a literature review

BACKGROUND

Neonatal hypoxic ischaemic encephalopathy due to perinatal asphyxia, can result in severe neurodevelopmental disability or mortality. Hypothermia is at present the only proven neuroprotective intervention. During hypothermia, the neonate may need a variety of drugs with their specific pharmacokinetic profile. The aim of this paper is to determine the effect that hypothermia for neonates suffering from hypoxic ischaemic encephalopathy has on the pharmacokinetics and to what extent dosing regimens need adjustments.

METHOD

A systematic search was performed on PubMed, Embase and Cochrane Library of literature (2000-2020) using a combination of the following search terms: therapeutic hypothermia, neonate, hypoxic ischemic encephalopathy and pharmacokinetics. Titles and abstracts were screened, and inclusion/exclusion criteria were applied. Finally, relevant full texts were read, and secondary inclusion was applied on the identified articles.

RESULTS

A total of 380 articles were retrieved, and 34 articles included after application of inclusion/exclusion criteria and duplicate removal, two additional papers were included as suggested by the reviewers. Twelve out of 36 studies on 15 compounds demonstrated a significant decrease in clearance, be it that the extent differs between routes of elimination and compounds, most pronounced for renal elimination (phenobarbital no difference, midazolam metabolite -21%, lidocaine -24%; morphine -21% to -47%, gentamicin -25% to -35%, amikacin -40%) during hypothermia. The data as retrieved in literature were subsequent compared with the dosing regimen as stated in the Dutch paediatric formulary.

CONCLUSION

Depending on the drug-specific disposition characteristics, therapeutic hypothermia in neonates with hypoxic ischaemic encephalopathy affects pharmacokinetics.

A Physiology-Based Pharmacokinetic Framework to Support Drug Development and Dose Precision During Therapeutic Hypothermia in Neonates

Therapeutic hypothermia (TH) is standard treatment for neonates (≥36 weeks) with perinatal asphyxia (PA) and hypoxic-ischemic encephalopathy. TH reduces mortality and neurodevelopmental disability due to reduced metabolic rate and decreased neuronal apoptosis. Since both hypothermia and PA influence physiology, they are expected to alter pharmacokinetics (PK). Tools for personalized dosing in this setting are lacking. A neonatal hypothermia physiology-based PK (PBPK) framework would enable precision dosing in the clinic. In this literature review, the stepwise approach, benefits and challenges to develop such a PBPK framework are covered. It hereby contributes to explore the impact of non-maturational PK covariates. First, the current evidence as well as knowledge gaps on the impact of PA and TH on drug absorption, distribution, metabolism and excretion in neonates is summarized. While reduced renal drug elimination is well-documented in neonates with PA undergoing hypothermia, knowledge of the impact on drug metabolism is limited. Second, a multidisciplinary approach to develop a neonatal hypothermia PBPK framework is presented. Insights on the effect of hypothermia on hepatic drug elimination can partly be generated from in vitro (human/animal) profiling of hepatic drug metabolizing enzymes and transporters. Also, endogenous biomarkers may be evaluated as surrogate for metabolic activity. To distinguish the impact of PA versus hypothermia on drug metabolism, in vivo neonatal animal data are needed. The conventional pig is a well-established model for PA and the neonatal Göttingen minipig should be further explored for PA under hypothermia conditions, as it is the most commonly used pig strain in nonclinical drug development. Finally, a strategy is proposed for establishing and fine-tuning compound-specific PBPK models for this application. Besides improvement of clinical exposure predictions of drugs used during hypothermia, the developed PBPK models can be applied in drug development. Add-on pharmacotherapies to further improve outcome in neonates undergoing hypothermia are under investigation, all in need for dosing guidance. Furthermore, the hypothermia PBPK framework can be used to develop temperature-driven PBPK models for other populations or indications. The applicability of the proposed workflow and the challenges in the development of the PBPK framework are illustrated for midazolam as model drug.

Pharmacokinetics and short-term safety of the selective NOS inhibitor 2-iminobiotin in asphyxiated neonates treated with therapeutic hypothermia

BACKGROUND

Neonatal encephalopathy following perinatal asphyxia is a leading cause for neonatal death and disability, despite treatment with therapeutic hypothermia. 2-Iminobiotin is a promising neuroprotective agent additional to therapeutic hypothermia to improve the outcome of these neonates.

METHODS

In an open-label study, pharmacokinetics and short-term safety of 2-iminobiotin were investigated in neonates treated with therapeutic hypothermia. Group A (n = 6) received four doses of 0.16 mg/kg intravenously q6h. Blood sampling for pharmacokinetic analysis and monitoring of vital signs for short-term safety analysis were performed. Data from group A was used to determine the dose for group B, aiming at an AUC_0-48 h of 4800 ng*h/mL.

RESULTS

Exposure in group A was higher than targeted (median AUC_0-48 h 9522 ng*h/mL); subsequently, group B (n = 6) received eight doses of 0.08 mg/kg q6h (median AUC_0-48 h 4465 ng*h/mL). No changes in vital signs were observed and no adverse events related to 2-iminobiotin occurred.

CONCLUSION

This study indicates that 2-iminobiotin is well tolerated and not associated with any adverse events in neonates treated with therapeutic hypothermia after perinatal asphyxia. Target exposure was achieved with eight doses of 0.08 mg/kg q6h. Optimal duration of therapy for clinical efficacy needs to be determined in future clinical trials.

Multiple Organ Dysfunction During Therapeutic Cooling of Asphyxiated Infants

The main purpose of therapeutic cooling is neuroprotection of asphyxiated infants with significant hypoxic-ischemic encephalopathy. However, to improve the overall outcome, it is necessary to properly manage the full range of multiple organ system complications found in asphyxiated infants undergoing therapeutic cooling. Every physiologic process in an asphyxiated infant can potentially be affected by the cooling treatment. The purpose of this review is to discuss the effect of cooling on neonatal physiology in the current recommended cooling range and the management thereof.

Population Pharmacokinetics of Gentamicin in Neonates with Hypoxemic-Ischemic Encephalopathy Receiving Controlled Hypothermia

OBJECTIVE

Identify population pharmacokinetics and pharmacodynamic target attainment of gentamicin in neonates with hypoxic-ischemic encephalopathy (HIE) undergoing controlled hypothermia (CH).

DESIGN

Prospective open-label pharmacokinetic study. Gentamicin concentrations were modeled and dosing regimens simulated for a 5000-patient neonatal population with HIE receiving CH using PMetrics, a nonparametric, pharmacometric modeling, and simulation package for R.

SETTING

A 189-bed children's tertiary care teaching hospital.

RESULTS

Twelve patients, 5 (42%) females and 7 (58%) males, met inclusion criteria with a median gestation age of 39.9 weeks (interquartile range [IQR] 38.5-40.2 wks) and a median birthweight (BW) of 3.3 kg (IQR 3.1-3.7 kg). Gentamicin concentrations were best described by a two-compartment model with first-order elimination with BW as a covariate on volume of distribution (Vd). The mean total body population clearance (CL) was 2.2 ± 0.7 ml/minute/kg, and the volume of the central compartment was 0.44 ± 0.06 L/kg. The R² , bias, and precision for the observed versus population predicted model were 0.917, 1.15, and 10.9 μg/ml; the R² , bias, and precision for the observed versus individual predicted model were 0.982, -0.132, and 0.932 μg/ml, respectively. The calculated mean population estimate for the total Vd was 0.96 ± 0.4 L/kg. The dosing regimen that most consistently produced a maximum concentration (C_max ) in the range of 10-12 mg/L with a minimum concentration (C_min ) level less than 2 mg/L was 5 mg/kg/dose given every 36 hours.

CONCLUSION

These data suggest the population pharmacokinetics of gentamicin in neonates with HIE receiving CH have an increase in gentamicin CL and are different from previous reports in neonates with HIE not receiving CH and/or neonates without HIE. This analysis suggests a dosing regimen of 5 mg/kg/dose every 36 hours results in a gentamicin C_max within the range of 10-12 mg/L with a C_min lower than 2 mg/L, which is appropriate for treating susceptible gram-negative organisms with minimum inhibitory concentrations of 1 mg/L or lower.

Effect of hypothermia treatment on gentamicin pharmacokinetics in neonates with hypoxic-ischaemic encephalopathy: A systematic review and meta-analysis

WHAT IS KNOWN AND OBJECTIVE

Hypothermia is the current standard therapy for asphyxiated neonates with hypoxic-ischaemic encephalopathy (HIE). Gentamicin is used for the empirical treatment of early-onset neonatal sepsis. We investigated the influence of hypothermia treatment on gentamicin pharmacokinetics and suggested the appropriate dosing recommendations for gentamicin in neonates with HIE receiving hypothermia treatment.

METHODS

We searched studies published until February 2017 in MEDLINE using PubMed, EMBASE and the Cochrane Library. Three independent reviewers screened the literature and extracted data from each study. All of the studies that reported the blood concentrations or pharmacokinetic parameters of gentamicin in hypothermic neonates with HIE were included in this review. Articles were excluded if they were not original research.

RESULT AND DISCUSSION

A total of 8 observational studies met the inclusion criteria. Meta-analyses were performed in which the mean difference of gentamicin for the trough concentration and clearance between hypothermic and normothermic neonates were 0.81 mg/L (95% confidence interval [-0.07, 1.69]) and -0.21 mL/kg/min (95% confidence interval [-0.31, -0.12]), respectively. The factors affecting gentamicin clearance in hypothermic neonates with HIE were gestational age, birthweight and serum creatinine.

WHAT IS NEW AND CONCLUSION

Gentamicin clearance is decreased in neonates with HIE receiving hypothermia treatment compared to those not receiving hypothermia treatment. Modified gentamicin dosing regimens are required to avoid potential toxicity related to higher concentrations during hypothermia treatment.

Severity of asphyxia is a covariate of phenobarbital clearance in newborns undergoing hypothermia

AIM

Phenobarbital (PB) pharmacokinetics (PK) in asphyxiated newborns show large variability, not only explained by hypothermia (HT). We evaluated potential relevant covariates of PK of PB in newborns treated with or without HT for hypoxic-ischemic encephalopathy (HIE).

METHODS

Clearance (CL), distribution volume (Vd) and elimination half-life (t_1/2) were calculated using one-compartment analysis. Covariates were clinical characteristics (weight, gestational age, hepatic, renal, and circulatory status), comedication and HIE severity [time to reach normal aEEG pattern (T_normaEEG), dichotomous, within 24 h] and asphyxia severity [severe aspyhxia = pH ≤7.1 + Apgar score ≤5 (5 min), dichotomous]. Student's t-test, two-way ANOVA, correlation and Pearson's chi-square test were used.

RESULTS

Forty newborns were included [14 non-HT; 26 HT with T_normaEEG <24 h in 14/26 (group_1-HT) and T_normaEEG ≥24 h in 12/26 (group_2-HT)]. Severe asphyxia was present in 26/40 [5/14 non-HT, 11/14 and 10/12 in both HT groups]. PB-CL, Vd and t_1/2 were similar between the non-HT and HT group. However, within the HT group, PB-CL was significantly different between group_1-HT and group_2-HT (p = .043). ANOVA showed that HT (p = .034) and severity of asphyxia (p = .038) reduced PB-CL (-50%).

CONCLUSION

The interaction of severity of asphyxia and HT is associated with a clinical relevant reduced PB-CL, suggesting the potential relevance of disease characteristics beyond HT itself.

Amikacin Pharmacokinetics To Optimize Dosing in Neonates with Perinatal Asphyxia Treated with Hypothermia

Aminoglycoside pharmacokinetics (PK) is expected to change in neonates with perinatal asphyxia treated with therapeutic hypothermia (PATH). Several amikacin dosing guidelines have been proposed for treating neonates with (suspected) septicemia; however, none provide adjustments for cases of PATH. Therefore, we aimed to quantify the differences in amikacin PK between neonates with and without PATH to propose suitable dosing recommendations. Based on amikacin therapeutic drug monitoring data collected retrospectively from neonates with PATH, combined with a published data set, we assessed the impact of PATH on amikacin PK by using population modeling. Monte Carlo and stochastic simulations were performed to establish amikacin exposures in neonates with PATH after dosing according to the current guidelines and according to proposed model-derived dosing guidelines. Amikacin clearance was decreased 40.6% in neonates with PATH, with no changes in volume of distribution. Simulations showed that increasing the dosing interval by 12 h results in a decrease in the percentage of neonates reaching toxic trough levels (>5 mg/liter), from 40 to 76% to 14 to 25%, while still reaching efficacy targets compared to the results of current dosing regimens. Based on this study, a 12-h increase in the amikacin dosing interval in neonates with PATH is proposed to correct for the reduced clearance, yielding safe and effective exposures. As amikacin is renally excreted, further studies into other renally excreted drugs may be required, as their clearance may also be impaired.

A Population Pharmacokinetic Analysis to Study the Effect of Therapeutic Hypothermia on Vancomycin Disposition in Children Resuscitated From Cardiac Arrest

OBJECTIVES

Limited data exist on the effects of therapeutic hypothermia on renal function and pharmacokinetics in pediatric patients after cardiac arrest. The objective was to describe the differences in vancomycin disposition in pediatric patients following cardiac arrest treated with either therapeutic hypothermia or normothermia using population pharmacokinetic modeling.

DESIGN

Single-center, retrospective cohort study.

SETTING

A tertiary care hospital pediatric and cardiac ICU.

PATIENTS

Fifty-two pediatric patients (30 d to 17 yr old) who experienced a cardiac arrest, received vancomycin, and were treated with therapeutic hypothermia (32-34°C) or normothermia (36.3-37.6°C) between January 1, 2010, and September 30, 2014, were reviewed.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A two-compartment model with linear elimination, weight effects on clearance, intercompartmental clearance (Q), central volume of distribution (V1), and peripheral volume of distribution (V2) adequately described the data despite high variability due to the small sample size. The typical value of clearance in this study was 4.48 L/hr (0.19 L/hr/kg) for a normothermic patient weighing 70 kg and a glomerular filtration rate of 90 mL/min/1.73 m. Patients treated with normothermia but with reduced or poor renal function (≤ 90 mL/min/1.73 m) had up to an 80% reduction in vancomycin clearance compared to those with normal renal function (90-140 mL/min/1.73 m). Patients with normal renal function but treated with therapeutic hypothermia versus normothermia experienced up to 25% reduction in vancomycin clearance. Patients treated with therapeutic hypothermia and with poor renal function experienced up to an 84% reduction in vancomycin clearance.

CONCLUSIONS

Patients receiving hypothermia and/or with decreased renal function had lower vancomycin clearances based on a retrospectively fitted two-compartment model in children who experience cardiac arrest.

The Evolving Paradigm of Individualized Postresuscitation Care After Cardiac Arrest

The postresuscitation period after a cardiac arrest is characterized by a wide range of physiological derangements. Variations between patients include preexisting medical problems, the underlying cause of the cardiac arrest, presence or absence of hemodynamic and circulatory instability, severity of the ischemia-reperfusion injury, and resuscitation-related injuries such as pulmonary aspiration and rib or sternal fractures. Although protocols can be applied to many elements of postresuscitation care, the widely disparate clinical condition of cardiac arrest survivors requires an individualized approach that stratifies patients according to their clinical profile and targets specific treatments to patients most likely to benefit. This article describes such an individualized approach, provides a practical framework for evaluation and triage at the bedside, and reviews concerns specific to all members of the interprofessional postresuscitation care team.

Effect of Hypothermia and Targeted Temperature Management on Drug Disposition and Response Following Cardiac Arrest: A Comprehensive Review of Preclinical and Clinical Investigations

Targeted temperature management (TTM) has been shown to reduce mortality and improve neurological outcomes in out-of-hospital cardiac arrest (CA) patients and in neonates with hypoxic-ischemic encephalopathy (HIE). TTM has also been associated with adverse drug events in the critically ill patient due to its effect on drug pharmacokinetics (PKs) and pharmacodynamics (PDs). We aim to evaluate the current literature on the effect of TTM on drug PKs and PDs following CA. MEDLINE/PubMed databases were searched for publications, which include the MeSH terms hypothermia, drug metabolism, drug transport, P450, critical care, cardiac arrest, hypoxic-ischemic encephalopathy, pharmacokinetics, and pharmacodynamics between July 2006 and October 2015. Twenty-three studies were included in this review. The studies demonstrate that hypothermia impacts PK parameters and increases concentrations of cytochrome-P450-metabolized drugs in the cooling and rewarming phase. Furthermore, the current data demonstrate a combined effect of CA and hypothermia on drug PK. Importantly, these effects can last greater than 4-5 days post-treatment. Limited evidence suggests hypothermia-mediated changes in the Phase II metabolism and the Phase III transport of drugs. Hypothermia also has been shown to potentially decrease the effect of specific drugs at the receptor level. Therapeutic hypothermia, as commonly deployed/applied during TTM, alters PK, and elevates concentrations of several commonly used medications. Hypothermia-mediated effects are an important factor when dosing and monitoring patients undergoing TTM treatment.

Birth Asphyxia and Hypoxic-Ischemic Brain Injury in the Preterm Infant

Birth asphyxia, also termed perinatal hypoxia-ischemia, is a modifiable condition as evidenced by improved outcomes of infants ≥36 weeks' gestation provided hypothermia treatment in randomized trials. Preterm animal models of asphyxia in utero demonstrate that hypothermia can provide short-term neuroprotection for the developing brain, supporting the interest in extending therapeutic hypothermia to preterm infants. This review focuses on the challenge of identifying preterm infants with perinatal asphyxia; the neuropathology of hypoxic-ischemic brain injury across extreme, moderate, and late preterm infants; and patterns of brain injury, use of therapeutic hypothermia, and approach to patient selection for neuroprotective treatments among preterm infants.

Decreased Morphine Clearance in Neonates With Hypoxic Ischemic Encephalopathy Receiving Hypothermia

Morphine is commonly used in neonates with hypothermic ischemic encephalopathy (HIE) during therapeutic hypothermia to provide comfort and analgesia. However, pharmacokinetic data to support morphine dosing in this vulnerable population are lacking. A prospective, 2-center clinical pharmacokinetic study of morphine was conducted in 20 neonates (birthweight, 1.82-5.3 kg) with HIE receiving hypothermia. Morphine dosing was per standard of care at each center. Morphine and glucuronide metabolites (morphine-3-glucuronide and morphine-6-gluronide) were measured via a validated dried blood spot liquid chromatography-tandem mass spectrometry assay. From the available concentration data (n = 106 for morphine; n = 106 for each metabolite), a population pharmacokinetic model was developed using nonlinear mixed-effects modeling. The clearance of morphine and glucuronide metabolites was best predicted by birthweight allometrically scaled using an exponent of 1.23. In addition, the clearance of each glucuronide metabolite was influenced by serum creatinine. No other significant predictors of clearance or volume of distribution were found. For a 3.5-kg neonate, morphine clearance was 0.77 L/h (CV, 48%), and the steady-state volume of distribution was 8.0 L (CV, 49%). Compared with previous studies in full-term newborns without HIE, morphine clearance was markedly lower. Dosing strategies customized for this vulnerable population will be needed. Applying the final population pharmacokinetic model, repeated Monte Carlo simulations (n = 1000 per simulation) were performed to evaluate various morphine dosing strategies that optimized achievement of morphine concentrations between 10 and 40 ng/mL. An optimized morphine loading dose of 50 μg/kg followed by a continuous infusion of 5 μg/kg/h was predicted across birthweights.

Altered gentamicin pharmacokinetics in term neonates undergoing controlled hypothermia

AIM(S)

Little is known about the pharmacokinetic (PK) properties of gentamicin in newborns undergoing controlled hypothermia after suffering from hypoxic−ischaemic encephalopathy due to perinatal asphyxia. This study prospectively evaluates and describes the population PK of gentamicin in these patients

METHODS

Demographic, clinical and laboratory data of patients included in a multicentre prospective observational cohort study (the ‘PharmaCool Study’) were collected. A non-linear mixed-effects regression analysis (nonmem®) was performed to describe the population PK of gentamicin. The most optimal dosing regimen was evaluated based on simulations of the final model.

RESULTS

A total of 47 patients receiving gentamicin were included in the analysis. The PK were best described by an allometric two compartment model with gestational age (GA) as a covariate on clearance (CL). During hypothermia the CL of a typical patient (3 kg, GA 40 weeks, 2 days post-natal age (PNA)) was 0.06 l kg−1 h−1 (inter-individual variability (IIV) 26.6%) and volume of distribution of the central compartment (Vc) was 0.46 l kg−1 (IIV 40.8%). CL was constant during hypothermia and rewarming, but increased by 29% after reaching normothermia (>96 h PNA).

CONCLUSIONS

This study describes the PK of gentamicin in neonates undergoing controlled hypothermia. The 29% higher CL in the normothermic phase compared with the preceding phases suggests a delay in normalization of CL after rewarming has occurred. Based on simulations we recommend an empiric dose of 5 mg kg−1 every 36 h or every 24 h for patients with GA 36–40 weeks and GA 42 weeks, respectively.

Activity of antimicrobial drugs against bacterial pathogens under mild hypothermic conditions

BACKROUND

Infections are a common problem in cardiac arrest survivors. Antimicrobial drugs are often administered in routine care during treatment of patients with mild therapeutic hypothermia (MTH). Because there is to date no evidence for the pharmacodynamics of antimicrobial drugs under MTH conditions, we investigated the in vitro activity of common antimicrobials against clinically relevant bacterial pathogens.

MATERIAL AND METHODS

Activities of antimicrobial drugs against clinically relevant bacterial pathogens were assessed in vitro by disk diffusion and broth microdilution assays at normothermic (37°C) and hypothermic (32°C) conditions.

RESULTS

Seventy-three bacterial isolates were tested in disk diffusion and 15 in broth microdilution assays. Mean differences in zone diameters and minimal inhibitory concentration ratios were 0.6 mm (95% confidence interval, 0.3-0.9 mm) and 0.98 (95% confidence interval, 0.95-1.02), respectively, meeting predefined criteria for equivalence of in vitro antimicrobial activity.

CONCLUSIONS

The presented data provide reassuring evidence that the intrinsic activity of antimicrobials seems to be unaltered in MTH. However, further studies evaluating the pharmacokinetics including target site concentrations of the respective drugs and in vivo pharmacodynamics are necessary to complement our understanding of the appropriate use of antimicrobials in MTH.

Physiological responses to hypothermia

Therapeutic hypothermia is the only treatment currently recommended for moderate or severe encephalopathy of hypoxic‒ischaemic origin in term neonates. Though the effects of hypothermia on human physiology have been explored for many decades, much of the data comes from animal or adult studies; the latter originally after accidental hypothermia, followed by application of controlled hypothermia after cardiac arrest or trauma, or during cardiopulmonary bypass. Though this work is informative, the effects of hypothermia on neonatal physiology after perinatal asphyxia must be considered in the context of a prolonged hypoxic insult that has already induced a number of significant physiological sequelae. This article reviews the effects of therapeutic hypothermia on respiratory, cardiovascular, and metabolic parameters, including glycaemic control and feeding requirements. The potential pitfalls of blood‒gas analysis and overtreatment of physiological changes in cardiovascular parameters are also discussed. Finally, the effects of hypothermia on drug metabolism are covered, focusing on how the pharmacokinetics, pharmacodynamics, and dosing requirements of drugs frequently used in neonatal intensive care may change during therapeutic hypothermia.

Management of neonatal morbidities during hypothermia treatment

Although the primary goal of therapeutic hypothermia is to improve the neurodevelopmental outcome in asphyxiated infants, optimal management of the full range of multi-organ system complications typically presented by such infants during cooling treatment is necessary for improvement of the overall outcome. For this reason, adequate knowledge of how cooling affects all organ systems of asphyxiated infants with multi-organ hypoxic-ischemic injury is essential. Adequate diagnostic resources, readily available subspecialty consultant services and trained multidisciplinary staff to monitor and manage multi-organ system complications in asphyxiated infants during therapeutic cooling must be ensured during implementation of a cooling program. As therapeutic hypothermia is being used more widely, centers should consider participation in national or international benchmarking of outcomes and short-term adverse events during cooling to facilitate continuous quality improvement efforts.

Pharmacokinetics of gentamicin in newborns with moderate-to-severe hypoxic-ischemic encephalopathy undergoing therapeutic hypothermia

OBJECTIVE

To investigate gentamicin pharmacokinetics in neonates with moderate-to-severe hypoxic-ischemic encephalopathy (HIE) who underwent therapeutic hypothermia (TH).

METHODS

Data were collected retrospectively from infants admitted between January 2007 and February 2011. Gentamicin was given at 2.5 mg/kg/dose q12h intravenously. Infants not eligible for TH underwent therapeutic normothermia (TN). After reviewing the data which showed >85 % of infants undergoing TH had gentamicin trough concentration >2 µg/ml at steady state, the gentamicin level monitoring protocol was modified since March 2011.

RESULTS

In the initial retrospective study, 15 TN infants were compared with 19 TH infants. There was significant difference in median gentamicin half-life (7.01 vs. 9.57 h). A higher proportion of infants in the TH group required dosage adjustment (8/15 vs. 17/19). After March 2011, gentamicin level taken 12-h post 1st dose was measured routinely and 18/22 infants had trough gentamicin levels >2 µg/ml. Their dosing intervals were extended to Q18h or beyond.

CONCLUSIONS

Infants with moderate-to-severe HIE who undergo TH may exhibit changes in the pharmacokinetic properties of gentamicin compared to infants who undergo TN. By measuring gentamicin level at 12-h after the first dose of 2.5 mg/kg/dose, appropriate dosing interval can be determined and the duration of exposure to toxic gentamicin level can be reduced.

The interplay between drugs and the kidney in premature neonates

The kidney plays a central role in the clearance of drugs. However, renal drug handling entails more than glomerular filtration and includes tubular excretion and reabsorption, and intracellular metabolization by cellular enzyme systems, such as the Cytochrome P450 isoenzymes. All these processes show maturation from birth onwards, which is one of the reasons why drug dosing in children is not simply similar to dosing in small adults. As kidney development normally finishes around the 36th week of gestation, being born prematurely will result in even more immature renal drug handling. Environmental effects, such as extra-uterine growth restriction, sepsis, asphyxia, or drug treatments like caffeine, aminoglycosides, or non-steroidal anti-inflammatory drugs, may further hamper drug handling in the kidney. Dosing in preterm neonates is therefore dependent on many factors that need to be taken into account. Drug treatment may significantly hamper postnatal kidney development in preterm neonates, just like renal immaturity has an impact on drug handling. The restricted kidney development results in a lower number of nephrons that may have several long-term sequelae, such as hypertension, albuminuria, and renal failure. This review focuses on the interplay between drugs and the kidney in premature neonates.

Tailored tools to improve pharmacotherapy in infants

INTRODUCTION

Extensive within-population variability is the essence of neonatal pharmacology. Despite this, infants remain one of the last therapeutic orphans. Together with additional legal initiatives, tailoring of already available tools (modeling, covariates, pharmacovigilance) may significantly improve pharmacotherapy in infants.

AREAS COVERED

Modeling approaches that hold the promise to improve pharmacotherapy in infants are between-compound extrapolation for compounds that undergo the same route of elimination and integration of time-varying physiology to adapt for the fast maturational changes. Besides these maturational covariates (size, age), newly emerging covariates relate to novel treatment modalities (extracorporeal circulation, hypothermia), environmental issues (microbiome, critical illness) or pharmacogenetics. All these covariates interact with the maturational variation. Finally, pharmacovigilance also needs to be tailored to the characteristics of this population. This relates to preventive strategies, signal detection and assessment of causality.

EXPERT OPINION

Knowledge on pharmacotherapy in infants is lagging. Tailoring available tools to the specific characteristics (maturation) and clinical needs (newly emerging covariates) of infants is feasible but needs creativity and a multidisciplinary collaboration between modelers, academia, clinical researchers and, obviously, the public, including parents.

Current status of hypothermia for hypoxemic ischemia of the newborn

This article reviews the pathophysiology of hypoxic-ischemic brain injury, and the impact of hypothermia as neuroprotection in the clinical setting. The results of trials performed in well resourced and mid and low resourced countries is presented. Infant and childhood outcome following hypothermia is provided. Biomarkers of outcome that are clinical, electrophysiological and imaging which will be helpful to clinicians are noted. Management of infants with encephalopathy, including safety of hypothermia is reviewed. The article concludes with knowledge gaps in neuroprotection and the future of hypothermia therapy.

Clinical pharmacology in neonates: small size, huge variability

Drug therapy is a powerful tool for improving neonatal outcome. Despite this, neonatologists still routinely prescribe off-label compounds developed for adults and extrapolate doses from those used for children or adults. Knowledge integration through pharmacokinetic modeling is a method that could improve the current situation. Such predictive models may convert neonatal pharmacotherapy from explorative to confirmatory. This can be illustrated by research projects related to the prediction of neonatal renal clearance and neonatal glucuronidation. This type of model will also improve the current knowledge of neonatal (patho)physiology. In the meanwhile, the fields of clinical pharmacology (e.g. pharmacokinetic/pharmacodynamic modeling and pharmacogenetics) and neonatology (e.g. whole-body cooling and the lower limit of viability) have both matured, resulting in new research topics. However, in order for the modeling and the newly emerging topics to become effective tools, they need to be tailored to the specific characteristics of neonates. Consequently, the field of neonatal pharmacotherapy needs dedicated neonatologists who continue to raise the awareness that off-label practices, eminence-based dosing regimens and the absence of neonatal drug formulations all reflect suboptimal care.

Managing the Complications of Mild Therapeutic Hypothermia in the Cardiac Arrest Patient

Mild therapeutic hypothermia (MTH) is used to lower the core body temperature of cardiac arrest (CA) patients to 32°C from 34°C to provide improved survival and neurologic outcomes after resuscitation from in-hospital or out-of-hospital CA. Despite the improved benefits of MTH, there are potentially unforeseen complications associated during management. Although the adverse effects are transient, the clinician should be aware of the associated complications when managing the patient receiving MTH. We aim to provide the medical community comprehensive information related to the potential complications of survivors of CA receiving MTH, as it is imperative for the clinician to understand the physiologic changes that take place in the patient receiving MTH and how to prepare for them and manage them if they do occur. We hope to provide information of how to manage these potential complications through both a review of the current literature and a reflection of our own experience.

Gentamicin pharmacokinetics in neonates undergoing therapeutic hypothermia

OBJECTIVE

To identify whether therapeutic hypothermia in newborns with hypoxic ischemic encephalopathy affects gentamicin pharmacokinetics.

STUDY DESIGN

Retrospective case-control study consisting of 16 neonates who underwent therapeutic hypothermia and received gentamicin with interpretable peak and trough serum levels obtained during the period of cooling and at steady state; comparator group consisting of 7 neonates met the criteria but did not undergo therapeutic hypothermia.

RESULTS

Significant differences in gentamicin pharmacokinetics were noted between the therapeutic hypothermia group and the comparator group in elimination rate constant (0.08/h versus 0.11/h; P < 0.01), elimination half-life (9.16 hours versus 6.56 hours; P < 0.01), and clearance (0.04 L/kg.h(-1) versus 0.05 L/kg.h(-1); P < 0.01), respectively. Higher gentamicin trough serum concentrations were seen with the therapeutic hypothermia group (1.68 mcg/mL versus 0.77 mcg/mL; P < 0.01).

CONCLUSIONS

Therapeutic hypothermia is associated with alterations in gentamicin pharmacokinetics, reducing gentamicin clearance by 25.5% in neonates with hypoxic ischemic encephalopathy, which may result in increased trough serum concentrations.

High-dose gentamicin in newborn infants: is it safe?

Dosing regimens often recommend lower gentamicin doses in neonates (3-5 mg/kg) than in older children (7 mg/kg or more) despite the higher volume of distribution in neonates. We studied an extended-interval high-dose (6 mg/kg) gentamicin regimen in a single tertiary neonatal unit from 2004-2012. During the first week of life, dosing interval was 24 h for term infants, 36 h for preterm infants with gestational age (GA) 29-36 weeks and 48 h for preterm infants with GA <29 weeks. After the first week of life, dosing interval was 24 h if corrected age (GA + postnatal age) ≥29 weeks and 36 h if corrected age <29 weeks. Outcome measures were trough plasma concentration (TPC), ototoxicity and prescription errors. In 546 treatment episodes, TPC was measured prior to the third gentamicin dose. There were 37 episodes (6.7 %) of prescription errors, mainly a too long dosing interval. We included 509 treatment episodes (440 infants) in the final analysis. Mean (standard deviation) gentamicin TPC during the first week of life was 1.1 (0.5) mg/L and after the first week of life 0.8 (0.6) mg/L. In 31 (6 %) episodes, TPC was ≥2.0 mg/L, predominantly among term infants with renal impairment. Thirty-eight patients failed the neonatal hearing screening, but only four of these 38 had permanent hearing loss. All four had a TPC <2.0 mg/L. Conclusions: This extended-interval high-dose gentamicin regimen was associated with low numbers of elevated TPCs, low numbers of prescription errors and no evidence for ototoxicity.

Every 36-h gentamicin dosing in neonates with hypoxic-ischemic encephalopathy receiving hypothermia

OBJECTIVE

To examine the impact of a change in the empiric gentamicin dose from 5 mg kg(-1) every 24 h (Q24 h period) to 5 mg kg every 36 h (Q36 h period) on target drug concentration achievement in neonates with hypoxic ischemic encephalopathy (HIE) receiving therapeutic hypothermia.

STUDY DESIGN

Gentamicin drug concentrations in neonates with HIE receiving therapeutic hypothermia were examined during two time periods in a retrospective chart review. During the initial treatment period (November 2007 to March 2010; n=29), neonates received Q24 h period. During the second treatment period (January 2011 to May 2012; n=23), the dose was changed to Q36 h period. Cooling criteria and protocol remained the same between treatment periods. Gentamicin drug concentrations including achievement of target trough concentrations (<2 mg l(-1)) were compared between treatment periods. Individual Bayesian estimates of gentamicin clearance were also compared.

RESULT

Neonates with an elevated trough concentration >2 mg l(-1) decreased from 38 to 4% with implementation of a Q36-h dosing interval (P<0.007). The mean gentamicin trough concentration was 2.0 ± 0.8 mg l(-1) during the Q24 h period and 0.9 ± 0.4 mg l(-1) during the Q36 h period (P<0.001). Peak concentrations were minimally impacted (Q24 h 11.4 ± 2.3 mg l(-1) vs Q36 h 10.0 ± 1.9 mg l(-1); P=0.05). The change in gentamicin trough concentration could not be accounted for by differences in gentamicin clearance between treatment periods (P=0.9).

CONCLUSION

A 5 mg kg(-1) every 36-h gentamicin dosing strategy in neonates with HIE receiving therapeutic hypothermia improved achievement of target trough concentration <2 mg l(-1), while still providing high peak concentration exposure.

Factors associated with permanent hearing impairment in infants treated with therapeutic hypothermia

OBJECTIVE

To define the incidence of hearing impairment, document plasma gentamicin concentrations, and identify factors associated with permanent hearing impairment in infants subjected to therapeutic hypothermia for moderate or severe neonatal encephalopathy.

STUDY DESIGN

Data were collected prospectively in a regional center providing therapeutic hypothermia. Cooled infants at ≥ 36 weeks gestation with moderate or severe neonatal encephalopathy were analyzed if a full dataset was available (n = 108), including clinical variables and gentamicin trough levels. Infants with hearing impairment were identified, and survivors were followed up with neurodevelopmental evaluation at age 18 months. Stepwise logistic regression identified factors associated with hearing impairment.

RESULTS

Nine infants died, and among the survivors, 10.1% developed a permanent hearing impairment. The trough gentamicin level was above the recommended cutoff of 2 mg/L in 37% of the infants in the entire cohort and in 90% of the infants with hearing impairment. Logistic regression analysis identified high trough gentamicin level, low cord pH, and hypoglycemia (<46.8 mg/dL) in the first postnatal hour as significantly associated with hearing impairment. The need for inotropic support was close to significant (P = .055).

CONCLUSION

Hearing impairment was a common finding among cooled infants. Plasma gentamicin levels were commonly >2 mg/L. Based on these findings, we propose changes in gentamicin dosing interval and trough level monitoring to minimize the risk of potentially toxic levels in cooled newborns.

Gentamicin pharmacokinetics and dosing in neonates with hypoxic ischemic encephalopathy receiving hypothermia

STUDY OBJECTIVE

To evaluate the pharmacokinetics of gentamicin in neonates with hypoxic ischemic encephalopathy (HIE) receiving hypothermia and to identify an empiric gentamicin dosing strategy in this population that optimizes achievement of target peak and trough concentrations.

DESIGN

Population pharmacokinetic study using retrospective medical record data.

SETTING

Tertiary neonatal intensive care unit.

PATIENTS

A total of 29 full-term neonates diagnosed with HIE treated with hypothermia who received gentamicin and underwent therapeutic drug monitoring

MEASUREMENT AND MAIN RESULTS

Patient demographics and gentamicin concentration data were retrospectively collected over a 2-year period. A population-based pharmacokinetic model was developed using nonlinear mixed-effects modeling (NONMEM). Using the developed model, Monte Carlo simulations were performed to evaluate the probability of achieving target peak (> 6 mg/L) and trough (< 2 mg/L) gentamicin concentrations for various potential dosing regimens. A one-compartment model best described the available gentamicin concentration data. Birthweight and serum creatinine significantly influenced gentamicin clearance. For the typical study neonate (birthweight 3.3 kg, serum creatinine 0.9 mg/dl), clearance was 0.034 L/hour/kg and volume was 0.52 L/kg. At a 24-hour dosing interval, Monte Carlo simulations predicted target gentamicin peak and trough concentrations could not be reliably achieved at any dose. At a 36-hour dosing interval, a dose of 4-5 mg/kg is predicted to achieve target gentamicin peak and trough concentrations in more than 90% of neonates.

CONCLUSIONS

Gentamicin clearance is decreased in neonates with HIE treated with hypothermia compared with previous reports in nonasphyxiated normothermic full-term neonates. A prolonged 36-hour dosing interval will be needed to achieve target gentamicin trough concentrations in this population. Further prospective evaluation of this dosing recommendation is needed.

Effect of hypothermia and extracorporeal life support on drug disposition in neonates

Extracorporeal membrane oxygenation (ECMO) is a valuable treatment modality in neonates with reversible cardiopulmonary failure in therapy-resistant pulmonary hypertension after perinatal asphyxia, septic shock or ECMO cardiopulmonary resuscitation. Neonates with severe perinatal asphyxia are currently treated with therapeutic hypothermia to improve neurological outcome. Consequently, therapeutic hypothermia may be indicated in the neonatal ECMO population. Both ECMO and hypothermia have been associated with changes in drug disposition. However, little is known about the combined effects of these treatment modalities. This review will explore the available literature, identify possible changes in pharmacokinetics and make suggestions for future research directions.

Population pharmacokinetics of phenobarbital in infants with neonatal encephalopathy treated with therapeutic hypothermia

OBJECTIVE

Phenobarbital is the first-line treatment for neonatal seizures. Many neonates with hypoxic ischemic encephalopathy are treated with therapeutic hypothermia, and about 40% have clinical seizures. Little is known about the pharmacokinetics of phenobarbital in infants with hypoxic ischemic encephalopathy who undergo therapeutic hypothermia. The objective of this study was to determine the effect of therapeutic hypothermia on phenobarbital pharmacokinetics, taking into account maturational changes.

SETTING

Level 3 neonatal ICU.

PATIENTS

Infants with hypoxic ischemic encephalopathy and suspected seizures, all treated with phenobarbital. Some of these infants also received treatment with therapeutic hypothermia.

INTERVENTIONS

None.

DESIGN

A retrospective cohort study of 39 infants with hypoxic ischemic encephalopathy treated with phenobarbital (20 were treated with therapeutic hypothermia and 19 were not).

MEASUREMENTS AND MAIN RESULTS

Data on phenobarbital plasma concentrations were collected in 39 subjects with hypoxic ischemic encephalopathy with or without therapeutic hypothermia. Using nonlinear mixed-effects modeling, population pharmacokinetics of phenobarbital were developed with a total of 164 plasma concentrations. A one-compartment model best described the pharmacokinetics. The clearance of phenobarbital was linearly related to body weight and matured with increasing age with a maturation half-life of 22.1 days. Therapeutic hypothermia did not influence the pharmacokinetic parameters of phenobarbital.

CONCLUSIONS

Therapeutic hypothermia does not influence the clearance of phenobarbital after accounting for weight and age. Standard phenobarbital dosing is appropriate for the initial treatment of seizures in neonates with hypoxic ischemic encephalopathy treated with therapeutic hypothermia.

Therapeutic hypothermia for neonatal encephalopathy

OPINION STATEMENT

Neonatal Hypoxic-ischemic encephalopathy in full term infants has been associated with a high risk for morbidity and mortality. The patho-physiology of brain injury following hypoxia-ischemia, noted in preclinical models, is a cascade of events resulting from excitotoxic and oxidative injury culminating in cell death. Hypothermia has been noted to be protective by inhibiting various events in the cascade of injury. Major randomized clinical trials in neonatal HIE have demonstrated reduction in death and disability and continued safety and efficacy of neuroprotection in childhood. There is now clinical and imaging evidence for hypothermia as neuroprotection. Hypothermia should be offered to term infants with either severe acidosis at birth or resuscitation needing continued ventilation and evidence of either moderate or severe encephalopathy within 6 hours of birth. The target temperature should be 33° to 34 °C and duration of cooling should be 72 hours, as per the published trials. Rewarming should be slow, at 0.5 °C per hour. Infants should have serial neurological examinations during and at the end of cooling and at discharge. Multiorgan function should be supported and hypocarbia should be avoided during ventilator therapy. If available, the amplitude integrated EEG should be obtained prior to cooling and following rewarming. All infants should have magnetic resonance brain imaging studies within 1 to 2 weeks of age. Information from the neurological examination, aEEG and MRI studies will be helpful in discussing prognosis with parents. All infants should be followed for a minimum of 18 months to evaluate growth parameters and neurodevelopment al outcome.

Hypoxic-ischemic encephalopathy and novel strategies for neuroprotection

This article covers the outcome of full-term infants with encephalopathy due to hypoxic-ischemia and pathophysiology of brain injury following hypoxic-ischemia. Clinical and imaging evidence for hypothermia for neuroprotection is presented. The outcome of infants with hypothermia for encephalopathy due to hypoxic-ischemia from recent trials is summarized. Facts regarding the clinical application of cooling obtained from the randomized trials and knowledge gaps in hypothermic therapy are presented. The review concludes with the future of hypothermia for neuroprotection.

The impact of extracorporeal life support and hypothermia on drug disposition in critically ill infants and children

Extracorporeal membrane oxygenation (ECMO) support is an established lifesaving therapy for potentially reversible respiratory or cardiac failure. In 10% of all pediatric patients receiving ECMO, ECMO therapy is initiated during or after cardiopulmonary resuscitation. Therapeutic hypothermia is frequently used in children after cardiac arrest, despite the lack of randomized controlled trials that show its efficacy. Hypothermia is frequently used in children and neonates during cardiopulmonary bypass (CPB). By combining data from pharmacokinetic studies in children on ECMO and CPB and during hypothermia, this review elucidates the possible effects of hypothermia during ECMO on drug disposition.

Pharmacokinetics and pharmacodynamics of medication in asphyxiated newborns during controlled hypothermia. The PharmaCool multicenter study

Background

In the Netherlands, perinatal asphyxia (severe perinatal oxygen shortage) necessitating newborn resuscitation occurs in at least 200 of the 180–185.000 newly born infants per year. International randomized controlled trials have demonstrated an improved neurological outcome with therapeutic hypothermia. During hypothermia neonates receive sedative, analgesic, anti-epileptic and antibiotic drugs. So far little information is available how the pharmacokinetics (PK) and pharmacodynamics (PD) of these drugs are influenced by post resuscitation multi organ failure and the metabolic effects of the cooling treatment itself. As a result, evidence based dosing guidelines are lacking. This multicenter observational cohort study was designed to answer the question how hypothermia influences the distribution, metabolism and elimination of commonly used drugs in neonatal intensive care.

Methods/Design

Multicenter cohort study. All term neonates treated with hypothermia for Hypoxic Ischemic Encephalopathy (HIE) resulting from perinatal asphyxia in all ten Dutch Neonatal Intensive Care Units (NICUs) will be eligible for this study. During hypothermia and rewarming blood samples will be taken from indwelling catheters to investigate blood concentrations of several antibiotics, analgesics, sedatives and anti-epileptic drugs. For each individual drug the population PK will be characterized using Nonlinear Mixed Effects Modelling (NONMEM). It will be investigated how clearance and volume of distribution are influenced by hypothermia also taking maturation of neonate into account. Similarly, integrated PK-PD models will be developed relating the time course of drug concentration to pharmacodynamic parameters such as successful seizure treatment; pain assessment and infection clearance.

Discussion

On basis of the derived population PK-PD models dosing guidelines will be developed for the application of drugs during neonatal hypothermia treatment. The results of this study will lead to an evidence based drug treatment of hypothermic neonatal patients. Results will be published in a national web based evidence based paediatric formulary, peer reviewed journals and international paediatric drug references.

Trial registration

NTR2529.

Therapeutic drug monitoring--the appropriate use of drug level measurement in the care of the neonate

Neonates and young infants are in a unique and dynamic pharmacokinetic state, in which they undergo relatively rapid maturational changes in drug absorption, distribution, metabolism, and excretion. In addition to these maturational changes, most drug pharmacokinetic studies in neonates show wide interindividual variability despite similar gestational and postnatal ages. Therapeutic drug monitoring is a necessary tool in the neonatal intensive care unit, despite the relative lack of outcome data. This article discusses therapeutic drug monitoring for several frequently used drugs in neonates.

Urinary erythropoietin concentrations after early short-term infusion of high-dose recombinant epo for neuroprotection in preterm neonates

BACKGROUND

High-dose recombinant human erythropoietin (rEpo) has first been administered in clinical trials for neuroprotection in very preterm neonates at high risk of brain injury and in (near-) term neonates with hypoxic-ischemic encephalopathy. However, recent trials in adults raised concerns about the safety of high-dose rEpo for neuro- and cardioprotection.

OBJECTIVES

To evaluate the putative accumulation or renal leakage of Epo as a function of developmental stage after repetitive early short-term infusion of high-dose rEpo (3 × 3,000 U/kg within 42 h after birth; NCT00413946) for neuroprotection in very preterm infants.

METHODS

Epo concentrations were measured using the ELISA technique in the first two consecutive urine specimens after each rEpo infusion.

RESULTS

Renal Epo excretion was significantly higher in preterm infants with gestational ages <29 weeks than in more mature infants and reached up to 23% of the administered rEpo within 8 h after each infusion. The urinary Epo concentration did not increase after three repetitive infusions of high-dose rEpo. The ratio of urinary Epo to total protein concentrations was the same in infants with gestational ages <29 weeks and in those with gestational ages ≥29 weeks.

CONCLUSIONS

Our data suggest that the higher renal Epo excretion in more immature infants may be attributed to a higher glomerular filtration leakage due to the lower maturation of the kidneys and argue against saturation kinetics after multiple doses of 3,000 U/kg rEpo. This information should be considered in future trials on the use of rEpo for neuroprotection in neonates.

Perinatal pharmacology: applications for neonatal neurology

The principles of clinical pharmacology also apply to neonates, but their characteristics warrant a tailored approach. We focus on aspects of both developmental pharmacokinetics (concentration/time relationship) and developmental pharmacodynamics (concentration/effect relationship) in neonates. We hereby aimed to link concepts used in clinical pharmacology with compound-specific observations (anti-epileptics, analgosedatives) in the field of neonatal neurology. Although in part anecdotal, we subsequently illustrate the relevance of developmental pharmacology in the field of neonatal neurology by a specific intervention (e.g. whole body cooling), specific clinical presentations (e.g. short and long term outcome following fetal exposure to antidepressive agents, the development of new biomarkers for fetal alcohol syndrome) and specific clinical needs (e.g. analgosedation in neonates, excitocytosis versus neuro-apoptosis/impaired synaptogenesis).

[Neuroprotection with hypothermia in the newborn with hypoxic-ischaemic encephalopathy. Standard guidelines for its clinical application]

Standardisation of hypothermia as a treatment for perinatal hypoxic-ischaemic encephalopathy is supported by current scientific evidence. The following document was prepared by the authors on request of the Spanish Society of Neonatology and is intended to be a guide for the proper implementation of this therapy. We discuss the difficulties that may arise when moving from the strict framework of clinical trials to clinical daily care: early recognition of clinical encephalopathy, inclusion and exclusion criteria, hypothermia during transport, type of hypothermia (selective head or systemic cooling) and side effects of therapy. The availability of hypothermia therapy has changed the prognosis of children with hypoxic-ischaemic encephalopathy and our choices of therapeutic support. In this sense, it is especially important to be aware of the changes in the predictive value of the neurological examination and the electroencephalographic recording in cooled infants. In order to improve neuroprotection with hypothermia we need earlier recognition of to recognise earlier the infants that may benefit from cooling. Biomarkers of brain injury could help us in the selection of these patients. Every single infant treated with hypothermia must be included in a follow up program in order to assess neurodevelopmental outcome.

Physiologic and pharmacologic considerations for hypothermia therapy in neonates

With mounting evidence that hypothermia is neuroprotective in newborns with hypoxic-ischemic encephalopathy (HIE), an increasing number of centers are offering this therapy. Hypothermia is associated with a wide range of physiologic changes affecting every organ system, and awareness of these effects is essential for optimum patient management. Lowering the core temperature also alters pharmacokinetic and pharmacodynamic properties of medications commonly used in asphyxiated neonates, necessitating close attention to drug efficacy and side effects. Rewarming introduces additional risks and challenges as the hypothermia-associated physiologic and pharmacologic changes are reversed. In this review we provide an organ system-based assessment of physiologic changes associated with hypothermia. We also summarize evidence from randomized controlled trials showing lack of serious adverse effects of moderate hypothermia therapy in term and near-term newborns with moderate-to-severe HIE. Finally, we review the effects of hypothermia on drug metabolism and clearance based on studies in animal models and human adults, and limited data from neonates.

The effect of therapeutic hypothermia on drug metabolism and response: cellular mechanisms to organ function

INTRODUCTION

Therapeutic hypothermia is being employed clinically due to its neuro-protective benefits. Both critical illness and therapeutic hypothermia significantly affect drug disposition, potentially contributing to drug-therapy and drug-disease interactions. Currently, there is limited information on the known alterations in drug concentration and response during mild hypothermia treatment, and there is a limited understanding of the specific mechanisms that underlie alterations in drug concentrations and the potential clinical importance of these changes.

AREAS COVERED

A systemic review of the effect of therapeutic hypothermia on drug metabolism, disposition and response is provided. Specifically, the clinical and preclinical evidence of the effects of therapeutic hypothermia on blood flow, specific hepatic metabolism pathways, transporter function, renal excretion, pharmacodynamics and the effects during rewarming are reviewed.

EXPERT OPINION

Available evidence demonstrates that mild hypothermia decreases the clearance of a variety of drugs with apparently little change in drug-protein binding. Recent evidence suggests that the magnitude of the change is elimination route specific. Further research is needed to determine the impact of these alterations on both drug concentration and response in order to optimize the therapeutic hypothermia in this vulnerable patient population.

Phenobarbital for neonatal seizures in hypoxic ischemic encephalopathy: a pharmacokinetic study during whole body hypothermia

PURPOSE

Therapeutic hypothermia has recently been introduced to treat term newborns with hypoxic-ischemic encephalopathy, of whom more than half have seizures. Phenobarbital is widely used to treat neonatal seizures, but it is unknown whether its pharmacokinetics is affected by hypothermia. We evaluated the influence of hypothermia on phenobarbital pharmacokinetics in asphyxiated newborns.

METHODS

Nineteen term asphyxiated newborns treated with mild whole body hypothermia, started within 6 h after birth and protracted for 72 h, received phenobarbital for clinical seizures. Treatment schedule consisted of a loading dose of 20 mg/kg, titrated to response, up to a maximum dose of 40 mg/kg, followed by a maintenance dose of 2.5 or 1.5 mg/kg every 12 h. Phenobarbital concentrations were measured on 28 dried blood spots in each newborn.

KEY FINDINGS

Eighteen newborns showed plasma concentrations within the reference range after receiving a loading dose of 20 mg/kg. In the remaining newborn, who had received a loading dose of 35 mg/kg, phenobarbital concentrations exceeded the upper reference limit. Phenobarbital concentrations reached a virtual steady state in all newborns. Pharmacokinetic parameters were then calculated. Minimum and maximum concentration (24.7 ± 8.8 and 30.63 ± 10.3 mg/L), average plasma concentration (27.37 ± 9.4 mg/L), and half-life (173.9 ± 62.5 h) were considerably higher than reported in literature for normothermic newborns. Pharmacokinetic parameters did not differ significantly between infants receiving different maintenance doses.

SIGNIFICANCE

Phenobarbital administered to newborns under whole body hypothermia results in higher plasma concentrations and longer half-lives than expected in normothermic newborns.

Systemic complications and hypothermia

Cooling for neonatal hypoxic-ischemic encephalopathy is a novel and promising neuroprotective therapy that requires significant understanding of how cooling affects all organ systems and interventions used to treat systemic complications of cooling in an intensive care setting. As cooling is used more widely and has been newly introduced in neonatal units, continued surveillance of its use in clinical practice is mandatory. Units offering cooling should strongly consider joining a registry (e.g. the Vermont-Oxford Neonatal Encephalopathy Registry in the USA or the TOBY Register in the UK) that facilitates benchmarking of short-term adverse effects and long-term outcomes of cooling and that supports local quality improvement efforts.