Population Pharmacokinetic Analysis of Gentamicin in Pediatric Extracorporeal Membrane Oxygenation

Pragmatic physiologically-based pharmacokinetic modeling to support clinical implementation of optimized gentamicin dosing in term neonates and infants: proof-of-concept

Introduction

Modeling and simulation can support dosing recommendations for clinical practice, but a simple framework is missing. In this proof-of-concept study, we aimed to develop neonatal and infant gentamicin dosing guidelines, supported by a pragmatic physiologically-based pharmacokinetic (PBPK) modeling approach and a decision framework for implementation.

Methods

An already existing PBPK model was verified with data of 87 adults, 485 children and 912 neonates, based on visual predictive checks and predicted-to-observed pharmacokinetic (PK) parameter ratios. After acceptance of the model, dosages now recommended by the Dutch Pediatric Formulary (DPF) were simulated, along with several alternative dosing scenarios, aiming for recommended peak (i.e., 8-12 mg/L for neonates and 15-20 mg/L for infants) and trough (i.e., <1 mg/L) levels. We then used a decision framework to weigh benefits and risks for implementation.

Results

The PBPK model adequately described gentamicin PK. Simulations of current DPF dosages showed that the dosing interval for term neonates up to 6 weeks of age should be extended to 36-48 h to reach trough levels <1 mg/L. For infants, a 7.5 mg/kg/24 h dose will reach adequate peak levels. The benefits of these dose adaptations outweigh remaining uncertainties which can be minimized by routine drug monitoring.

Conclusion

We used a PBPK model to show that current DPF dosages for gentamicin in term neonates and infants needed to be optimized. In the context of potential uncertainties, the risk-benefit analysis proved positive; the model-informed dose is ready for clinical implementation.

Pharmacokinetics of Commonly Used Antimicrobials in Critically Ill Pediatric Patients During Extracorporeal Membrane Oxygenation: A Systematic Review

PURPOSE

Adequate dosing of antimicrobials is critical to properly treat infections and limit development of resistance and adverse effects. Limited guidance exist for antimicrobial dosing adjustments in patients requiring extracorporeal membrane oxygenation (ECMO) therapy, particularly in the pediatric population. A systematic review was conducted to delineate the pharmacokinetics (PK) and pharmacodynamics (PD) of antimicrobials in critically ill neonates and children requiring ECMO therapy.

METHODS

Medline, EMBASE, Global Health and All EBM Reviews databases were queried. Grey literature was examined. All clinical studies reporting PK/PD parameters of antimicrobials in critically ill pediatric patients treated with ECMO were included, except for case reports and congress abstracts. Two independent reviewers applied the inclusion and exclusion criteria. Reviewers were then paired to independently extract data and evaluate the methodological quality of studies using the ROBINS-I tool and the compliance with ClinPK reporting guidelines. Patient and study characteristics, key PK/PD findings, details of ECMO circuits and co-treatments were summarized qualitatively. Broad dosing recommendations were formulated based on the available data for specific antimicrobials.

RESULTS

Twenty-nine clinical studies were included; most were observational and uncontrolled. Patient characteristics and co-treatments were often missing. The effect of ECMO on PK/PD parameters of antimicrobials varied depending on the drugs and population studied. It was only possible to formulate dosing recommendations for a few antimicrobials given the paucity of data, its overall low quality and heterogeneity in reporting.

CONCLUSION

Limited data exists on the PK/PD of antimicrobials during ECMO therapy in the pediatric population. Rigorously designed population PK studies are required to establish empiric dosing guidelines for antimicrobials in patients requiring this therapeutic modality. The use of therapeutic drug monitoring for antimicrobials in pediatric patients on ECMO should be encouraged to optimize dosing.

TRIAL REGISTRY

PROSPERO registration number: CRD42018099992 (Registered: July 24th 2018).

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.

Clinical Pharmacokinetics of Gentamicin in Various Patient Populations and Consequences for Optimal Dosing for Gram-Negative Infections: An Updated Review

Gentamicin is an aminoglycoside antibiotic with a small therapeutic window that is currently used primarily as part of short-term empirical combination therapy. Gentamicin dosing schemes still need refinement, especially for subpopulations where pharmacokinetics can differ from pharmacokinetics in the general adult population: obese patients, critically ill patients, paediatric patients, neonates, elderly patients and patients on dialysis. This review summarizes the clinical pharmacokinetics of gentamicin in these patient populations and the consequences for optimal dosing of gentamicin for infections caused by Gram-negative bacteria, highlighting new insights from the last 10 years. In this period, several new population pharmacokinetic studies have focused on these subpopulations, providing insights into the typical values of the most relevant pharmacokinetic parameters, the variability of these parameters and possible explanations for this variability, although unexplained variability often remains high. Both dosing schemes and pharmacokinetic/pharmacodynamic (PK/PD) targets varied widely between these studies. A gentamicin starting dose of 7 mg/kg based on total body weight (or on adjusted body weight in obese patients) appears to be the optimal strategy for increasing the probability of target attainment (PTA) after the first administration for the most commonly used PK/PD targets in adults and children older than 1 month, including critically ill patients. However, evidence that increasing the PTA results in higher efficacy is lacking; no studies were identified that show a correlation between estimated or predicted PK/PD target attainment and clinical success. Although it is unclear if performing therapeutic drug monitoring (TDM) for optimization of the PTA is of clinical value, it is recommended in patients with highly variable pharmacokinetics, including patients from all subpopulations that are critically ill (such as elderly, children and neonates) and patients on intermittent haemodialysis. In addition, TDM for optimization of the dosing interval, targeting a trough concentration of at least < 2 mg/L but preferably < 0.5–1 mg/L, has proven to reduce nephrotoxicity and is therefore recommended in all patients receiving more than one dose of gentamicin. The usefulness of the daily area under the plasma concentration–time curve for predicting nephrotoxicity should be further investigated. Additionally, more research is needed on the optimal PK/PD targets for efficacy in the clinical situations in which gentamicin is currently used, that is, as monotherapy for urinary tract infections or as part of short-term combination therapy.

Disposition of gentamicin and amikacin in extracorporeal membrane oxygenation using a heparin-coated filter: An in vitro assessment

Disposition of gentamicin and amikacin during extracorporeal membrane oxygenation has not been addressed in in vitro models. The HLS Advanced 7.0^® circuit with the Cardio Help^® monitor, Getinge, was used. The 5-L central compartment (CC) was loaded with gentamicin and amikacin at a targeted concentration of 40 and 80 mg/L in the same bag prior connection to the circuit. Samples were collected in the CC, the inlet and outlet ports from 15 min to 6 h post-connection. Pharmacokinetic analyses were performed using the NeckEpur^® method. Analysis of results of gentamicin and amikacin showed in the filter-pump block (i) the extremely low value of the extraction coefficients, (ii) similar values of the areas under the curve (AUCs) at the inlet and outlet ports, (iii) using the Wilcoxon matched pairs signed rank test no significant differences of the inlet-outlet concentrations in the filter-pump. In the whole system (i) the amounts recovered in the CC at the end of the 6-h session were not significantly different from the initial values, (ii) the extremely low values of the total clearance of gentamicin and amikacin from the CC in comparison with the measured simulated blood flowrate, (iii) the lack of significant time-concentration interactions in the CC and the inlet and outlet ports. These findings allow concluding no detectable adsorption of gentamicin and amikacin occurred in the HLS Advanced 7.0 circuit.

Antibiotics and ECMO in the Adult Population—Persistent Challenges and Practical Guides

Extracorporeal membrane oxygenation (ECMO) is an emerging treatment modality associated with a high frequency of antibiotic use. However, several covariables emerge during ECMO implementation, potentially jeopardizing the success of antimicrobial therapy. These variables include but are not limited to: the increased volume of distribution, altered clearance, and adsorption into circuit components, in addition to complex interactions of antibiotics in critical care illness. Furthermore, ECMO complicates the assessment of antibiotic effectiveness as fever, or other signs may not be easily detected, the immunogenicity of the circuit affects procalcitonin levels and other inflammatory markers while disrupting the immune system. We provided a review of pharmacokinetics and pharmacodynamics during ECMO, emphasizing practical application and review of patient-, illness-, and ECMO hardware-related factors.

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.

[Effect of extracorporeal membrane oxygenation on pharmacokinetics of antimicrobial drugs: recent progress and recommendations]

Extracorporeal membrane oxygenation (ECMO) is an effective means to provide life support for patients with severe respiratory or heart failure. Existing studies have shown that ECMO may affect the metabolic process of some drugs by drug adsorption, increasing the apparent distribution volume and changing the clearance rate of the drugs. This review summarizes the recent progress in the studies of the effect of ECMO on the pharmacokinetics of antibacterial and antifungal drugs. For the antibacterial drugs, it is recommended that the dose of teicoplanin, imipenem, and linezolid should be increased during ECMO support, while the dose of azithromycin, ciprofloxacin, and tigecycline should not be modified for the time being. Currently studies on pharmacokinetic changes of antifungal drugs during ECMO support remain limited. Voriconazole can be absorbed substantially by ECMO due to its high lipophilicity, and higher doses are therefore recommended. The dose of micafungin also needs to be increased in children undergoing ECMO. However, current evidence concerning the dose of caspofungin and fluconazole are limited, and it is not clear whether the routine dose should be adjusted during ECMO support.

The role of antibiotic pharmacokinetic studies performed post-licensing

Post-licensing pharmacometric studies can provide a better understanding of the pharmacokinetic (PK) alterations in special patient populations and may lead to better clinical outcomes. Some patient populations exhibit markedly different pathophysiology to general ward patients or healthy individuals. This may be developmental (paediatric patients), a manifestation of an underlying disease pathology (patients with obesity or haematological malignancies) or due to medical interventions (critically ill patients receiving extracorporeal therapies). This paper outlines the factors that affect the PK of special patient populations and describes some novel methods of antimicrobial administration that may increase antimicrobial concentrations at the site of infection and improve treatment of severe infection.

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.