Quantitative clinical pharmacology practice for optimal use of antibiotics during the neonatal period

Pharmacokinetic and Pharmacodynamic Considerations of Antibiotic Use in Neonates

The selection of an appropriate dose of a given antibiotic for a neonate not only requires knowledge of the drug's basic pharmacokinetic (PK) and pharmacodynamic (PD) properties but also the profound effects that organ development might have on the volume of distribution and clearance, both of which may affect the PK/PD of a drug. Interest has grown in alternative antibiotic dosing strategies that are better aligned with the antibiotic's PK and PD properties. These strategies should be used in conjunction with minimum inhibitory concentration measurements and therapeutic drug monitoring to measure their potential success. They can also guide the clinician in tailoring the delivery of antibiotics to suit an individual patient's needs. Model-informed precision dosing, such as Bayesian forecasting dosing software (which incorporates PK/PD population models), may be utilized to optimize antibiotic exposure in neonatal populations. Consequently, optimizing the antibiotic dose and exposure in each newborn requires expertise in different fields. It drives the collaboration of physicians together with lab technicians and quantitative clinical pharmacologists.

Physiologically Based Pharmacokinetic Modeling in Neonates: Current Status and Future Perspectives

Rational drug use in special populations is a clinical problem that doctors and pharma-cists must consider seriously. Neonates are the most physiologically immature and vulnerable to drug dosing. There is a pronounced difference in the anatomical and physiological profiles be-tween neonates and older people, affecting the absorption, distribution, metabolism, and excretion of drugs in vivo, ultimately leading to changes in drug concentration. Thus, dose adjustments in neonates are necessary to achieve adequate therapeutic concentrations and avoid drug toxicity. Over the past few decades, modeling and simulation techniques, especially physiologically based pharmacokinetic (PBPK) modeling, have been increasingly used in pediatric drug development and clinical therapy. This rigorously designed and verified model can effectively compensate for the deficiencies of clinical trials in neonates, provide a valuable reference for clinical research design, and even replace some clinical trials to predict drug plasma concentrations in newborns. This review introduces previous findings regarding age-dependent physiological changes and pathological factors affecting neonatal pharmacokinetics, along with their research means. The application of PBPK modeling in neonatal pharmacokinetic studies of various medications is also reviewed. Based on this, we propose future perspectives on neonatal PBPK modeling and hope for its broader application.

Simplified Dosing Regimens for Gentamicin in Neonatal Sepsis

Background: The effectiveness of antibiotics for the treatment of severe bacterial infections in newborns in resource-limited settings has been determined by empirical evidence. However, such an approach does not warrant optimal exposure to antibiotic agents, which are known to show different disposition characteristics in this population. Here we evaluate the rationale for a simplified regimen of gentamicin taking into account the effect of body size and organ maturation on pharmacokinetics. The analysis is supported by efficacy data from a series of clinical trials in this population.

Methods: A previously published pharmacokinetic model was used to simulate gentamicin concentration vs. time profiles in a virtual cohort of neonates. Model predictive performance was assessed by supplementary external validation procedures using therapeutic drug monitoring data collected in neonates and young infants with or without sepsis. Subsequently, clinical trial simulations were performed to characterize the exposure to intra-muscular gentamicin after a q.d. regimen. The selection of a simplified regimen was based on peak and trough drug levels during the course of treatment.

Results: In contrast to current World Health Organization guidelines, which recommend gentamicin doses between 5 and 7.5 mg/kg, our analysis shows that gentamicin can be used as a fixed dose regimen according to three weight-bands: 10 mg for patients with body weight <2.5 kg, 16 mg for patients with body weight between 2.5 and 4 kg, and 30 mg for those with body weight >4 kg.

Conclusion: The choice of the dose of an antibiotic must be supported by a strong scientific rationale, taking into account the differences in drug disposition in the target patient population. Our analysis reveals that a simplified regimen is feasible and could be used in resource-limited settings for the treatment of sepsis in neonates and young infants with sepsis aged 0–59 days.

Population Pharmacokinetic Analysis and Dose Regimen Optimization in Japanese Infants with an Extremely Low Birth Weight

Vancomycin is a synthetic antibiotic effective against Gram-positive pathogens. Although the clinical applicability of vancomycin for infants has been increasing, the pharmacokinetic data for vancomycin in extremely low-birth-weight infants are limited. The aim of this study was to construct a population pharmacokinetics model for vancomycin in extremely-low-birth-weight infants and establish an optimal dosage regimen. We enrolled children aged less than 1 year with a birth weight of less than 1,000 g and body weight at vancomycin prescription of less than 1,500 g. Pharmacokinetic data from 19 patients were analyzed, and a population pharmacokinetics model was developed using nonlinear mixed-effects modeling software. Goodness-of-fit plots, a nonparametric bootstrap analysis, and a prediction-corrected visual predictive check were employed to evaluate the final model. The dosage regimen was optimized based on the final model. The pharmacokinetic data fit a one-compartment model with first-order elimination, and body weight and estimated serum creatinine level were used as significant covariates. In a simulation using the final model, the optimal dosage regimen, especially when the serum creatinine level (>0.6 mg/dl) was high, was 5.0 to 7.5 mg/kg of body weight twice a day every 12 h; this was required to reduce the dosage compared with that in previous studies. The recommended doses based on the current target time course concentration curves may not be appropriate for extremely-low-birth-weight infants.

Dose Rationale for Amoxicillin in Neonatal Sepsis When Referral Is Not Possible

Background

Despite the widespread use of amoxicillin in young children, efforts to establish the feasibility of simplified dosing regimens in resource-limited settings have relied upon empirical evidence of efficacy. Given the antibacterial profile of beta-lactams, understanding of the determinants of pharmacokinetic variability may provide a more robust guidance for the selection of a suitable regimen. Here we propose a simplified dosing regimen based on pharmacokinetic-pharmacodynamic principles, taking into account the impact of growth, renal maturation and disease processes on the systemic exposure to amoxicillin.

Materials and Methods

A meta-analytical modeling approach was applied to allow the adaptation of an existing pharmacokinetic model for amoxicillin in critically ill adults. Model parameterization was based on allometric concepts, including a maturation function. Clinical trial simulations were then performed to characterize exposure, as defined by secondary pharmacokinetic parameters (AUC, C_max, C_min) and T>MIC. The maximization of the T>MIC was used as criterion for the purpose of this analysis and results compared to current WHO guidelines.

Results

A two-compartment model with first order absorption and elimination was found to best describe the pharmacokinetics of amoxicillin in the target population. In addition to the changes in clearance and volume distribution associated with demographic covariates, our results show that sepsis alters drug distribution, leading to lower amoxicillin levels and longer half-life as compared to non-systemic disease conditions. In contrast to the current WHO guidelines, our analysis reveals that amoxicillin can be used as a fixed dose regimen including two weight bands: 125 mg b.i.d. for patients with body weight < 4.0 kg and 250 mg b.i.d. for patients with body weight ≥ 4.0 kg.

Conclusions

In addition to the effect of developmental growth and renal maturation, sepsis also alters drug disposition. The use of a model-based approach enabled the integration of these factors when defining the dose rationale for amoxicillin. A simplified weight-banded dosing regimen should be considered for neonates and young infants with sepsis when referral is not possible.

Administración y preparación de antimicrobianos en una unidad chilena de cuidados neonatales

Objetivo: Describir la preparación, administración y monitorización de los antimicrobianos utilizados en una Unidad de Cuidados Neonatales en Santiago de Chile. Métodos: Estudio descriptivo. Se realizó la aplicación de un instrumento a 20 matronas de neonatología de una Unidad Chilena de Cuidados Neonatales (UCHCN) en 2018, para recopilar información respecto a once variables en la preparación y administración de antimicrobianos. El estudio abarcó tres variables principales: preparación, mantención y monitorización de los antimicrobianos. Resultados: Se recopiló información de 14 antimicrobianos, de los cuales la presentación del 92.8% de ellos era inyectable y el 78.2% de los encuestados reconocía el valor de la unidad de dosificación del medicamento. Mantención 85.7% de los antimicrobianos son eliminados luego de su preparación. Para dilución se utiliza mayormente la solución fisiológica en un 76.9% de los casos y el volumen utilizado de diluyente y concentración final varió según cada medicamento. Un 92.8% de los antimicrobianos se administra por vía endovenosa y todos a través de una bomba de jeringa. Monitorización específica de la administración sólo se realiza en un 7.2% de ellos. Conclusiones: Debido a las variabilidades encontradas en los procesos de mantención, dilución y monitorización es que se propone la creación o el mejoramiento y difusión de protocolos locales, para evitar efectos adversos o complicaciones y así resguardar la seguridad de los pacientes.

Optimizing Antibiotic Drug Therapy in Pediatrics: Current State and Future Needs

The selection of the right antibiotic and right dose necessitates clinicians understand the contribution of pharmacokinetic variability stemming from age-related physiologic maturation and the pharmacodynamics to optimize drug exposure for clinical response. The complexity of selecting the right dose arises from the multiplicity of pediatric age groups, from premature neonates to adolescents. Body size and age (which relate to organ function) must be incorporated to optimize antibiotic dosing in this vulnerable population. In the effort to optimize and individualize drug dosing regimens, clinical pharmacometrics that incorporate population-based pharmacokinetic modeling, Bayesian estimation, and Monte Carlo simulations are utilized as a quantitative approach to understanding and predicting the pharmacology and clinical and microbiologic efficacy of antibiotics. In addition, opportunistic study designs and alternative blood sampling strategies can serve as practical approaches to ensure successful conduct of pediatric studies. This review article examines relevant literature on optimization of antibiotic pharmacotherapy in pediatric populations published within the last decade. Specific pediatric antibiotic data, including beta-lactam antibiotics, aminoglycosides, and vancomycin, are critically evaluated.

Neonates are not just little children and need more finesse in dosing of antibiotics

OBJECTIVES

Neonates are not just little children. They need more finesse in decisions on when to treat, which antibiotics to use and how to dose these antibiotics.

METHODS

Representative compounds of three major classes of antibiotics (beta-lactams, aminoglycosides, glycopeptides) are discussed in a narrative review to illustrate the recent progress in the knowledge on PK and its covariates (how to dose).

RESULTS

This knowledge can subsequently be converted to targeted exposure dosing regimens. This is because it is reasonable to postulate that pharmacodynamics (PD) of antibiotics are similar in neonates to that in other populations if a similar concentration-time profile and targeted exposure are attained. However, this approach has its limitations, since the clinical response may be different in neonates because of maturational differences in innate immunity or toxicity. These dosing regimens should at least be validated.

CONCLUSION

Relevant information on the PK of antibiotics and its covariates have been generated, but the next steps are to validate the dosing regimens suggested, and consider more sophisticated dosing regimens. This approach should subsequently pave the way to conduct comparative studies to assess the efficacy and safety of these commonly used drugs in neonates.

Vancomycin therapeutic drug monitoring and population pharmacokinetic models in special patient subpopulations

Vancomycin is a fundamental antibiotic in the management of severe Gram-positive infections. Inappropriate vancomycin dosing is associated with therapeutic failure, bacterial resistance and toxicity. Therapeutic drug monitoring (TDM) is acknowledged as an important part of the vancomycin therapy management, at least in specific patient subpopulations, but implementation in clinical practice has been difficult because there are no consensus and agglutinator documents. The aims of the present work are to present an overview of the current knowledge on vancomycin TDM and population pharmacokinetic (PPK) models relevant to specific patient subpopulations. Based on three published international guidelines (American, Japanese and Chinese) on vancomycin TDM and a bibliographic review on available PPK models for vancomycin in distinct subpopulations, an analysis of evidence was carried out and the current knowledge on this topic was summarized. The results of this work can be useful to redirect research efforts to address the detected knowledge gaps. Currently, TDM of vancomycin presents a moderate level of evidence and practical recommendations with great robustness in neonates, pediatric and patients with renal impairment. However, it is important to investigate in other subpopulations known to present altered vancomycin pharmacokinetics (eg neurosurgical, oncological and cystic fibrosis patients), where evidence is still unsufficient.

Quantitative Analysis of Gentamicin Exposure in Neonates and Infants Calls into Question Its Current Dosing Recommendations

Optimal dosing of gentamicin in neonates is still a matter of debate despite its common use. We identified gentamicin dosing regimens from eight international guidelines and seven Swiss neonatal intensive care units. The dose per administration, the dosing interval, the total daily dose, and the demographic characteristics between guidelines were compared. There was considerable variability with respect to dose (4 to 6 mg/kg), dosing interval (24 h to 48 h), total daily dose (2.5 to 6 mg/kg/day), and patient demographic characteristics that were used to calculate individualized dosing regimens. A model-based simulation study in 1071 neonates was performed to determine the achievement of efficacious peak gentamicin concentrations according to predefined MICs (Cmax/MIC ≥ 10) and safe trough concentrations (Cmin ≤ 2 mg/liter) with recommended dosing regimens. MIC targets of 0.5 and 1 mg/liter were used. Dosing optimization was performed giving priority to the first day of treatment and with the goal of simplifying dosing. Current gentamicin neonatal guidelines allow to achieve effective peak concentrations for MICs ≤ 0.5 mg/liter but not higher. Model-based simulations indicate that to attain peak gentamicin concentrations of ≥10 mg/liter, a dose of 7.5 mg/kg should be administered using an extended dosing interval regimen. Trough concentrations of ≤2 mg/liter can be maintained with a dosing interval of 36 to 48 h in neonates according to gestational and postnatal age. For treatment beyond 3 days, therapeutic drug monitoring is advised to maintain adequate serum concentrations.

Population pharmacokinetics of vancomycin and AUC-guided dosing in Chinese neonates and young infants

OBJECTIVES

To develop a population pharmacokinetic (PK) model for vancomycin in Chinese neonates and infants less than 2 months of age (young infants) with a wide gestational age range, in order to determine the appropriate dosing regimen for this population.

METHODS

We performed a retrospective chart review of patients from the neonatal intensive care unit (NICU) at Children's Hospital of Fudan University to identify neonates and young infants treated with vancomycin from May 2014 to May 2017. Vancomycin concentrations and covariates were utilized to develop a one-compartment model with first-order elimination. The predictive performance of the final model was assessed by both internal and external evaluation, and the relationship between trough concentration and AUC_0-24 was investigated. Monte Carlo simulations were performed to design an initial dosing schedule targeting an AUC_0-24 ≥ 400.

RESULTS

The analysis included a total of 330 concentration-time data points from 213 neonates and young infants with gestational age (GA) and body weight of 25-42 weeks and 0.88-5.1 kg, respectively. Body weight, postmenstrual age (PMA) and serum creatinine level were found to be important factors explaining the between-subject variability in vancomycin PK parameters for this population. Both internal and external evaluation supported the prediction of the final vancomycin PK model. The typical population parameter estimates of clearance and distribution volume for an infant weighing 2.73 kg with a PMA of 39.8 weeks and serum creatinine of 0.28 mg/dL were 0.103 L/h/kg and 0.58 L/kg, respectively. Although vancomycin serum trough concentrations were predictive of the AUC, considerable variability was observed in the achievement of an AUC_0-24/MIC of ≥400. For MIC values of ≤0.5 mg/L, AUC_0-24/MIC ≥400 was achieved for 95% of the newborn infants with vancomycin troughs of 5-10 mg/L. When the MIC increased to 1 mg/L, only 15% of the patients with troughs of 5-10 mg/L achieved AUC_0-24/MIC ≥400. For MIC values of 2 mg/L, no infants achieved the target. Simulations predicted that a dose of at least 14 and 15 mg/kg every 12 h was required to attain the target AUC_0-24 ≥ 400 in 90% of infants with a PMA of 30-32 and 32-34 weeks, respectively. This target was also achieved in 93% of simulated infants in the oldest PMA groups (36-38 and 38-40 weeks, respectively) when the dosing interval was extended to 8 h. For infants with a PMA ≥44 weeks, a dose increase to 18 mg/kg every 8 h was needed. The trough concentrations of 5-15 mg/L were highly predictive of an AUC_0-24 of ≥400 when treating invasive MRSA infections with an MIC of ≤1 mg/L.

CONCLUSIONS

The PK parameters for vancomycin in Chinese infants younger than 2 months of age were estimated using the model developed herein. This model has been used to predict individualized dosing regimens in this vulnerable population in our hospital. A large external evaluation of our model will be conducted in future studies.

Key Components for Antibiotic Dose Optimization of Sepsis in Neonates and Infants

Sepsis in neonates and infants remains a major cause of death despite a decline in child mortality and morbidity over the last decades. A key factor in further reducing poor clinical outcomes is the optimal use of antibiotics in sepsis management. Developmental changes such as maturation of organ function and capacity of drug metabolizing enzymes can affect the pharmacokinetic profile and therefore the antibiotic exposure and response in neonates and infants. Optimal antibiotic treatment of sepsis in neonates and young infants is dependent on several key components such as the determination of treatment phase, the administered dose and the resulted drug exposure and microbiological response. During the initial phase of suspected sepsis, the primary focus of empirical treatment is to assure efficacy. Once bacterial infection as the cause of sepsis is confirmed the focus shifts toward a targeted treatment, ensuring an optimal balance between efficacy and safety. Interpretation of antibiotic exposure and microbiological response in neonates and infants is multifaceted. The response or treatment effect can be determined by the microbiological parameters (MIC) together with the characteristics of the pathogen (time- or concentration dependent). The antibiotic response is influenced by the properties of the causative pathogen and the unique characteristics of the vulnerable patient population such as reduced humoral response or reduced skin barrier function. Therapeutic drug monitoring (TDM) of antibiotics may be used to increase effectiveness while maximizing safety and minimizing the toxicity, but requires expertise in different fields and requires collaborations between physicians, lab technicians, and quantitative clinical pharmacologists. Understanding these clinical, pharmacological, and microbiological components and their underlying relationship can provide a scientific basic for proper antibiotic use and reduction of antibiotic resistance in neonates and infants. This highlights the necessity of a close multidisciplinary collaboration between physicians, pharmacists, clinical pharmacologists and microbiologist to assure the optimal utilization of antibiotics in neonates and young infants.

The amikacin research program: a stepwise approach to validate dosing regimens in neonates

INTRODUCTION

For safe and effective use of antibacterial agents in neonates, specific knowledge on the pharmacokinetics (PK) and its covariates is needed. This necessitates a stepwise approach, including prospective validation. Areas covered: We describe our approach throughout almost two decades to improve amikacin exposure in neonates. A dosing regimen has been developed and validated using pharmacometrics, considering current weight, postnatal age, perinatal asphyxia, and ibuprofen use. This regimen has been developed based on clinical and therapeutic drug monitoring (TDM) data collected during routine care, and subsequently underwent prospective validation. A similar approach has been scheduled to quantify the impact of hypothermia. Besides plasma observations, datasets on deep compartment PK were also collected. Finally, the available literature on developmental toxicology (hearing, renal) of amikacin is summarized. Expert opinion: The amikacin model reflects a semi-physiological function for glomerular filtration. Consequently, this model can be used to develop dosing regimens for other aminoglycosides or to validate physiology-based pharmacokinetic models. Future studies should explore safety with incorporation of covariates like pharmacogenetics, biomarkers, and long-term outcomes. This includes a search for mechanisms of developmental toxicity. Following knowledge generation and grading the level of evidence in support of data, dissemination and implementation initiatives are needed.

Clinical research in neonates and infants: Challenges and perspectives

To date, up to 65% of drugs used in neonates and infants are off-label or unlicensed, as they were implemented in clinical care without the usual regulatory phases of pharmacological drug development. Pharmacotherapy in this age group is still mainly based on the individual clinical expertise of specialized pediatricians. Pharmacological trials involving neonates are indeed more difficult to perform: appropriate dosing is hampered by the rapid physiological changes occurring at this stage of development, and the selection of proper end-points and biomarkers is complicated by the limited knowledge of the pathophysiology of the specific diseases of infancy. Moreover, there are many ethical challenges in planning and conducting drug studies in pediatric patients (especially in newborns and infants). In the current review, we address some challenges and discuss possible perspectives to stimulate scientific and clinical pharmacological research in neonates and infants. We hereby aim to illustrate the add on value of the regulatory framework for model-based neonatal medicinal development currently used in Europe and the United States. We provide several examples of successful recent pharmacological trials performed in neonates and infants. In these examples, success was ensured by the implementation of specific pharmacokinetic assessments, thanks to accurate drug dosing achieved with a combination of dose validation, population pharmacokinetics and mathematical models of drug clearance and distribution; moreover, age-specific pharmacodynamics was considered via appropriate evaluations of drug efficacy with end-points adapted to the peculiar pathophysiology of diseases in this age group. These "pharmacological" challenges add to the ethical challenges that are always present in planning and conducting clinical studies in neonates and infants and support the opinion that clinical research in pediatrics should be evaluated by ad hoc ethical committees with specific expertise.