Phenobarbital pharmacokinetics in neonates and infants during extracorporeal membrane oxygenation

Phenobarbital as a Sedation Strategy to Reduce Opioid and Benzodiazepine Burden in Neonatal Extracorporeal Membrane Oxygenation

OBJECTIVE

The study aims to describe our experience with the implementation of phenobarbital as a primary sedation strategy during neonatal extracorporeal membrane oxygenation (ECMO).

STUDY DESIGN

Retrospective chart review in a level IV neonatal intensive care unit between 2011 and 2021 comparing neonatal ECMO patients before and after the implementation of a sedation-analgesia (SA) protocol using scheduled phenobarbital as the primary sedative. Groups were compared for neonatal and ECMO characteristics, cumulative SA doses, and in-hospital outcomes. Comparison between groups was performed using Mann-Whitney test on continuous variables and chi-square on nominal variables.

RESULTS

Forty-two patients were included, 23 preprotocol and 19 postprotocol. Birth, pre-ECMO, and ECMO clinical characteristics were similar between groups except for a lower birth weight in the postprotocol group (p = 0.024). After standardization of phenobarbital SA protocol, there was a statistically significant reduction in median total morphine dose (31.38-17.65 mg/kg, p = 0.006) and median total midazolam dose (36.21-6.36 mg/kg, p < 0.001). There was also a reduction in median total days on morphine by 7.5 days (p = 0.026) and midazolam by 6.6 days (p = 0.003). There were no differences in ECMO duration or in-hospital outcomes between groups.

CONCLUSION

In this cohort, short-term use of phenobarbital as primary sedation strategy during neonatal ECMO was associated with reduced opioid and midazolam burden. Such reduction, however, did not affect in-hospital outcomes.

KEY POINTS

· Prolonged sedation on ECMO puts infants at risk for iatrogenic withdrawal.. · Phenobarbital is a feasible sedation strategy for ECMO.. · Phenobarbital sedation strategy may mitigate risk by decreasing opioid and midazolam burden..

Analysis of Adverse Events Following Phenobarbital Administration for Pediatric Patients Categorized by One-Year Age Increments Using the U.S. Food and Drug Administration Adverse Event Reporting System

Background Organ and body development greatly varies in pediatric patients from year to year. Therefore, the incidence of each adverse event following phenobarbital (PB) administration would vary with age. However, in clinical trials, increasing the sample size of pediatric patients in each age group has been challenging. Therefore, previous studies were conducted by dividing pediatric patients into three or four age groups based on the development stage. Although these results were useful in clinical settings, information on adverse events that occurred at one-year age increments in pediatric patients could further enhance treatment and care. Objectives This study investigated in one-year age increments the occurrence tendency of each adverse event following PB administration in pediatric patients. Methods This study used data obtained from the U.S. Food and Drug Administration Adverse Event Reporting System (FAERS). Two inclusion criteria were set: (1) treatment with PB between January 2004 and June 2023 and (2) age 0-15 years. Using the cutoff value obtained using the Wilcoxon-Mann-Whitney test by the minimum p-value approach, this study explored changes in the occurrence tendency of each adverse event in one-year age increments. At the minimum p-value of <0.05, the age corresponding to this p-value was determined as the cutoff value. Conversely, at the minimum p-value of ≥0.05, the cutoff value was considered nonexistent. Results This study investigated all types of adverse events and explored the cutoff value for each adverse event. We identified 34, 16, 15, nine, five, five, eight, three, and eight types of adverse events for the cutoff values of ≤3/>3, ≤4/>4, ≤5/>5, ≤6/>6, ≤7/>7, ≤8/>8, ≤9/>9, ≤10/>10, and ≤11/>11 years, respectively. Conclusions This study demonstrated that adverse events requiring attention in pediatric patients varied with age. The findings help in the improvement of treatment and care in the pediatric clinical settings.

Population pharmacokinetics in critically ill neonates and infants undergoing extracorporeal membrane oxygenation: a literature review

Extracorporeal membrane oxygenation (ECMO) increases circulating blood volume, causes capillary leak and temporarily alters kidney function. Consequently, pharmacokinetics (PK) can be affected. When applied to neonates and infants, additional dose adjustments are a major concern, as the volume of distribution (Vd) is already generally greater for water-soluble drugs and the clearance (Cl) of drugs eliminated by glomerular filtration is reduced. A systematic search was performed on MEDLINE (1994-2022) using a combination of the following search terms: "pharmacokinetics", "extracorporeal membrane oxygenation" and "infant, newborn" using Medical Subject Headings search strategy. Nine out of 18 studies on 11 different drugs (vancomycin, meropenem, fluconazole, gentamicin, midazolam, phenobarbital, theophylline, clonidine, morphine, cefotaxime and cefepime) recommended dose increase/decrease by determining PK parameters. In other studies, it has been suggested to adjust the dose intervals. While the elimination half-life (t_1/2) and Vd mostly increased for all drugs, the Cl of the drugs has been shown to have variability except for midazolam and morphine. There are a limited number of population PK studies in neonates and infants undergoing ECMO circuits. Despite some divergences, the general pattern suggests an increase in Vd and t_1/2, an increased, stable or decreased Cl, and an increase in variability. Consequently, and if possible, therapeutic drug monitoring and target concentration intervention are strongly recommended to determine appropriate exposure and doses for neonates and infants undergoing ECMO support.

Pharmacokinetic Drug-Drug Interactions among Antiepileptic Drugs, Including CBD, Drugs Used to Treat COVID-19 and Nutrients

Anti-epileptic drugs (AEDs) are an important group of drugs of several generations, ranging from the oldest phenobarbital (1912) to the most recent cenobamate (2019). Cannabidiol (CBD) is increasingly used to treat epilepsy. The outbreak of the SARS-CoV-2 pandemic in 2019 created new challenges in the effective treatment of epilepsy in COVID-19 patients. The purpose of this review is to present data from the last few years on drug–drug interactions among of AEDs, as well as AEDs with other drugs, nutrients and food. Literature data was collected mainly in PubMed, as well as google base. The most important pharmacokinetic parameters of the chosen 29 AEDs, mechanism of action and clinical application, as well as their biotransformation, are presented. We pay a special attention to the new potential interactions of the applied first-generation AEDs (carbamazepine, oxcarbazepine, phenytoin, phenobarbital and primidone), on decreased concentration of some medications (atazanavir and remdesivir), or their compositions (darunavir/cobicistat and lopinavir/ritonavir) used in the treatment of COVID-19 patients. CBD interactions with AEDs are clearly defined. In addition, nutrients, as well as diet, cause changes in pharmacokinetics of some AEDs. The understanding of the pharmacokinetic interactions of the AEDs seems to be important in effective management of epilepsy.

Evaluation of an ex-vivo neonatal extracorporeal membrane oxygenation circuit on antiepileptic drug sequestration

Antiepileptic dosing information used to manage neonatal patients receiving extracorporeal membrane oxygenation (ECMO) is limited. The objective of this study is to quantify the extent of sequestration of various antiepileptic drugs using an ex-vivo neonatal ECMO circuit. Two neonatal closed-loop ECMO circuits were prepared using a Rotaflow centrifugal pump, custom polyvinylchloride tubing and a Quadrox-i Neonatal membrane oxygenator. After 5 minutes of circuit priming and stabilization with normal saline/albumin or expired human whole blood, single boluses of levetiracetam (200 mg), lacosamide (20 mg), and phenytoin (200 mg) were injected into the circuit. To account for spontaneous drug degradation, two polyvinylchloride beakers were filled with normal saline/albumin or expired human whole blood and equivalent antiepileptic drug doses were prepared. Simultaneous pharmacokinetic samples were collected from the control solution and the pre-centrifugal pump, pre-oxygenator, and post-oxygenator sampling ports from each circuit. Similar drug recovery profiles were observed among the three sampling sites investigated. Percent drug sequestration after a 24-hour circuit flow period was relatively similar between the two different circuits and ranged between 5.5%-13.2% for levetiracetam, 18.4%-22.3% for lacosamide, and 24.5%-30.2% for phenytoin. A comparison at 12 and 24 hours demonstrated similar percent drug sequestration across all three drugs in each circuit. Percent drug sequestrations for levetiracetam and lacosamide were less than 20% and for phenytoin were as high as 30% based on the sampling following single bolus dose administration into a neonatal ECMO circuit. Careful consideration of patient clinical status should be taken in consideration when optimizing antiepileptic therapy in neonates receiving ECMO.

What is the Best Predictor of Phenobarbital Pharmacokinetics to Use for Initial Dosing in Neonates?

Phenobarbital is a first-line treatment of various seizure types in newborns. Dosage individualization maximizing the proportion of patients with drug levels in therapeutic range or sufficient treatment response is still challenging. The aim of this review was to summarize the available evidence on phenobarbital pharmacokinetics in neonates and to identify its possible covariates suitable for individualization of initial drug dosing. Several covariates have been considered: body weight and height, body surface area, gestational and postnatal age, laboratory parameters of renal and hepatic functions, asphyxia, therapeutic hypothermia, extracorporeal membrane oxygenation (ECMO), drug interactions, and genetic polymorphisms. The most frequently studied and well-founded covariate for the estimation of phenobarbital dosing is actual body weight. Loading dose of 15-20 mg/kg followed by a maintenance dose of 3-5 mg/kg/day seems to be accurate. However, the evidence for the other covariates with respect to dosing individualization is not sufficient. Doses at the lower limit of suggested range should be preferred in patients with severe asphyxia, while the upper limit of the range should be targeted in neonates receiving ECMO support.

New Methods Used in Pharmacokinetics and Therapeutic Monitoring of the First and Newer Generations of Antiepileptic Drugs (AEDs)

The review presents data from the last few years on bioanalytical methods used in therapeutic drug monitoring (TDM) of the 1st-3rd generation and the newest antiepileptic drug (AEDs) cenobamate in patients with various forms of seizures. Chemical classification, structure, mechanism of action, pharmacokinetic data and therapeutic ranges for total and free fractions and interactions were collected. The primary data on bioanalytical methods for AEDs determination included biological matrices, sample preparation, dried blood spot (DBS) analysis, column resolution, detection method, validation parameters, and clinical utility. In conclusion, the most frequently described method used in AED analysis is the LC-based technique (HPLC, UHPLC, USLC) combined with highly sensitive mass detection or fluorescence detection. However, less sensitive UV is also used. Capillary electrophoresis and gas chromatography have been rarely applied. Besides the precipitation of proteins or LLE, an automatic SPE is often a sample preparation method. Derivatization was also indicated to improve sensitivity and automate the analysis. The usefulness of the methods for TDM was also highlighted.

Population Pharmacokinetics of Phenobarbital in Neonates and Infants on Extracorporeal Membrane Oxygenation and the Influence of Concomitant Renal Replacement Therapy

The objective of this study was to describe the pharmacokinetics (PK) of intravenous phenobarbital in neonates and infants on extracorporeal membrane oxygenation (ECMO) and to provide dosing recommendations in this population. We performed a retrospective single-center PK study of phenobarbital in neonates and infants on ECMO between January 1, 2014, and December 31, 2018. We developed a population PK model using nonlinear mixed-effects modeling, performed simulations using the final PK parameters, and determined optimal dosing based on attainment of peak and trough concentrations between 20 and 40 mg/L. We included 35 subjects with a median (range) age and weight of 14 days (1-154 days) and 3.4 kg (1.6-8.1 kg), respectively. A total of 194 samples were included in the analysis. Five children (14%) contributing 30 samples (16%) were supported by continuous venovenous hemodiafiltration (CVVHDF). A 1-compartment model best described the data. Typical clearance and volume of distribution for a 3.4-kg infant were 0.038 L/h and 3.83 L, respectively. Clearance increased with age and CVVHDF. Although on ECMO, phenobarbital clearance in children on CVVHDF was 6-fold higher than clearance in children without CVVHDF. In typical subjects, a loading dose of 30 mg/kg/dose followed by maintenance doses of 6-7 mg/kg/day administered as divided doses every 12 hours reached goal concentrations. Age did not impact dosing recommendations. However, higher doses were needed in children on CVVHDF. We strongly recommend therapeutic drug monitoring in children on renal replacement therapy (excluding slow continuous ultrafiltration) while on ECMO.

Repair of soft tissue and extensor tendon defects on the dorsum of the hand by transfer of dorsal foot flap and extensor digitorum brevis tendon in a 3-year-old child: A case report

RATIONALE

Repair of soft tissue defects on the dorsum of the hand with accompanying tendon defects is a challenging problem in clinical practice.

PATIENT CONCERNS

Here, we describe the case of a 3-year-old boy with a 1-week old soft tissue injury with infection due to a soft tissue defect on the dorsum of his right hand, and further describe its treatment.

DIAGNOSIS

A diagnosis of a soft tissue defect of the dorsum with extensor tendon defects in the fore, middle, ring, and little fingers of the right hand was made.

INTERVENTIONS

The defects were repaired using a dorsal foot flap combined with the extensor digitorum brevis tendon, under spinal anesthesia, and a small dose of the sedative phenobarbital (Lumina) was administered via pump injection after the surgery.

OUTCOMES

The patient was followed-up for 6 months. The shape of the dorsal hand flap recovered satisfactorily and the skin color was almost normal. Protective sensation was restored and the tendon graft functioned well in vivo. Satisfactory outcomes were achieved in the flexion and extension of each finger.

LESSONS

This case study provides evidence that for soft tissue defects on the dorsum of the hand with tendon defects, 1-stage transfer of a dorsal foot flap with the extensor digitorum brevis tendon can be effective for recovery of appearance and extensor function. In case of infant patients, postoperative use of low-dose sedation can effectively reduce the risk of vascular crisis, thus promoting survival of the flap graft, and ensuring the success of the operation.

Population Pharmacokinetics of IV Phenobarbital in Neonates After Congenital Heart Surgery

OBJECTIVES

To develop a population pharmacokinetic model for IV phenobarbital in neonates following cardiac surgery and perform simulations to identify optimal dosing regimens.

DESIGN

Retrospective single-center pharmacokinetic study.

SETTING

Cardiac ICU at Children's Hospital of Philadelphia.

PATIENTS

Consecutive neonates who received greater than or equal to one dose of IV phenobarbital and had greater than or equal to one phenobarbital concentration drawn per standard of care from June 15, 2012, to October 15, 2018.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A population pharmacokinetic model was developed using nonlinear mixed-effects modeling. Simulations were performed using the final model variables. Optimal phenobarbital loading doses were determined based on attainment of peak and maintenance concentrations between 20 and 40 mg/L. A total of 37 neonates contributed 159 pharmacokinetic samples. The median (range) weight, postmenstrual age, and postnatal age were 3.2 kg (1.3-3.8), 39 2/7 weeks (28 2/7 to 42 6/7), and 5 days (0-26 d), respectively. Twelve patients (32%) were on extracorporeal membrane oxygenation. An one-compartment model best described the data. The final population pharmacokinetic model included (1) weight and postnatal age for clearance and (2) weight, extracorporeal membrane oxygenation, and albumin for volume of distribution. In neonates not on extracorporeal membrane oxygenation, loading doses of 30 and 20 mg/kg reached goal concentration with albumin values less than or equal to 3 and 3.5 mg/dL, respectively. Loading doses of 30 mg/kg reached goal concentration on extracorporeal membrane oxygenation regardless of albumin values. Maintenance doses of 4-5 mg/kg/d reached goal concentration in all neonates.

CONCLUSIONS

In neonates following cardiac surgery, phenobarbital clearance increased with postnatal age. Volume of distribution increased with extracorporeal membrane oxygenation and lower albumin values. Loading doses of 30 mg/kg on extracorporeal membrane oxygenation and 20-30 mg/kg without extracorporeal membrane oxygenation were needed to reach goal concentration based on simulations.

Pharmacokinetics Alterations in Critically Ill Pediatric Patients on Extracorporeal Membrane Oxygenation: A Systematic Review

Objectives: This study aimed to identify alterations in pharmacokinetics in children on extracorporeal membrane oxygenation (ECMO), identify knowledge gaps, and inform future pharmacology studies. Data Sources: We systematically searched the databases MEDLINE, CINAHL, and Embase from earliest publication until November 2018 using a controlled vocabulary and keywords related to "ECMO" and "pharmacokinetics," "pharmacology," "drug disposition," "dosing," and "pediatrics." Study Selection: Inclusion criteria were as follows: study population aged <18 years, supported on ECMO for any indications, received any medications while on ECMO, and reported pharmacokinetic data. Data Extraction: Clearance and/or volume of distribution values were extracted from included studies. Data Synthesis: Forty-one studies (total patients = 574) evaluating 23 drugs met the inclusion criteria. The most common drugs studied were antimicrobials (n = 13) and anticonvulsants (n = 3). Twenty-eight studies (68%) were conducted in children <1 year of age. Thirty-three studies (80%) were conducted without intra-study comparisons to non-ECMO controls. Increase in volume of distribution attributable to ECMO was demonstrated for nine (56%) drugs: cefotaxime, gentamicin, piperacillin/tazobactam, fluconazole, micafungin, levetiracetam, clonidine, midazolam, and sildenafil (range: 23-345% increase relative to non-ECMO controls), which may suggest the need for higher initial dosing. Decreased volume of distribution was reported for two drugs: acyclovir and ribavirin (50 and 69%, respectively). Decreased clearance was reported for gentamicin, ticarcillin/clavulanate, bumetanide, and ranitidine (range: 26-95% decrease relative to non-ECMO controls). Increased clearance was reported for caspofungin, micafungin, clonidine, midazolam, morphine, and sildenafil (range: 25-455% increase relative to non-ECMO controls). Conclusions: There were substantial pharmacokinetic alterations in 70% of drugs studied in children on ECMO. However, studies evaluating pharmacokinetic changes of many drug classes and those that allow direct comparisons between ECMO and non-ECMO patients are still lacking. Systematic evaluations of pharmacokinetic alterations of drugs on ECMO that incorporate multidrug opportunistic trials, physiologically based pharmacokinetic modeling, and other methods are necessary for definitive dose recommendations. Trial Registration Prospero Identifier: CRD42019114881.

Drug Disposition and Pharmacotherapy in Neonatal ECMO: From Fragmented Data to Integrated Knowledge

Extracorporeal membrane oxygenation (ECMO) is a lifesaving support technology for potentially reversible neonatal cardiac and/or respiratory failure. As the survival and the overall outcome of patients rely on the treatment and reversal of the underlying disease, effective and preferentially evidence-based pharmacotherapy is crucial to target recovery. Currently limited data exist to support the clinicians in their every-day intensive care prescribing practice with the contemporary ECMO technology. Indeed, drug dosing to optimize pharmacotherapy during neonatal ECMO is a major challenge. The impact of the maturational changes of the organ function on both pharmacokinetics (PK) and pharmacodynamics (PD) has been widely established over the last decades. Next to the developmental pharmacology, additional non-maturational factors have been recognized as key-determinants of PK/PD variability. The dynamically changing state of critical illness during the ECMO course impairs the achievement of optimal drug exposure, as a result of single or multi-organ failure, capillary leak, altered protein binding, and sometimes a hyperdynamic state, with a variable effect on both the volume of distribution (Vd) and the clearance (Cl) of drugs. Extracorporeal membrane oxygenation introduces further PK/PD perturbation due to drug sequestration and hemodilution, thus increasing the Vd and clearance (sequestration). Drug disposition depends on the characteristics of the compounds (hydrophilic vs. lipophilic, protein binding), patients (age, comorbidities, surgery, co-medications, genetic variations), and circuits (roller vs. centrifugal-based systems; silicone vs. hollow-fiber oxygenators; renal replacement therapy). Based on the potential combination of the above-mentioned drug PK/PD determinants, an integrated approach in clinical drug prescription is pivotal to limit the risks of over- and under-dosing. The understanding of the dose-exposure-response relationship in critically-ill neonates on ECMO will enable the optimization of dosing strategies to ensure safety and efficacy for the individual patient. Next to in vitro and clinical PK data collection, physiologically-based pharmacokinetic modeling (PBPK) are emerging as alternative approaches to provide bedside dosing guidance. This article provides an overview of the available evidence in the field of neonatal pharmacology during ECMO. We will identify the main determinants of altered PK and PD, elaborate on evidence-based recommendations on pharmacotherapy and highlight areas for further research.