Extended-interval gentamicin: population pharmacokinetics in pediatric critical illness

The impact of extracorporeal support on antimicrobial pharmacokinetics in critically ill neonatal and paediatric patients: A systematic review

OBJECTIVES

Infections represent a major risk for critically ill neonatal and paediatric patients requiring extracorporeal life-saving support such as extracorporeal membrane oxygenation (ECMO) and/or continuous renal replacement therapies (CRRT). Patient outcomes rely on achieving target antimicrobial concentrations. In critically ill adults on extracorporeal support, suboptimal antimicrobial concentrations have been shown to be common. Our objective was to systematically review antimicrobial pharmacokinetic studies in critically ill term neonatal and paediatric patients receiving ECMO and/or CRRT and compare them to similar cohorts of patients not receiving ECMO or CRRT.

METHODS

Studies published between 1990 and 2022 were identified through systematic searches in PUBMED, Embase, Web of Science, Medline, Google Scholar and CINAHL. Studies were included which provided antimicrobial pharmacokinetic parameters (volume of distribution and clearance) in the neonatal and paediatric patients receiving ECMO and/or CRRT. Studies were excluded if no antimicrobial pharmacokinetic parameters were described or could be calculated.

RESULTS

Forty-four pharmacokinetic studies were identified describing 737 patients, with neonatal patients recruited in 70% of the ECMO studies and <1% of the CRRT studies. Of all the studies, 50% were case reports or case series. The pharmacokinetics were altered for gentamicin, daptomycin, ceftolozane, micafungin, voriconazole, cefepime, fluconazole, piperacillin, and vancomycin, although considerable patient variability was described.

CONCLUSION

Significant gaps remain in our understanding of the pharmacokinetic alterations in neonatal and paediatric patients receiving ECMO and CRRT support.

When will the Glomerular Filtration Rate in Former Preterm Neonates Catch up with Their Term Peers?

AIMS

Whether and when glomerular filtration rate (GFR) in preterms catches up with term peers is unknown. This study aims to develop a GFR maturation model for (pre)term-born individuals from birth to 18 years of age. Secondarily, the function is applied to data of different renally excreted drugs.

METHODS

We combined published inulin clearance values and serum creatinine (Scr) concentrations in (pre)term born individuals throughout childhood. Inulin clearance was assumed to be equal to GFR, and Scr to reflect creatinine synthesis rate/GFR. We developed a GFR function consisting of GFRbirth (GFR at birth), and an Emax model dependent on PNA (with GFRmax, PNA50 (PNA at which half ofGFR max is reached) and Hill coefficient). The final GFR model was applied to predict gentamicin, tobramycin and vancomycin concentrations.

RESULT

In the GFR model, GFRbirth varied with birthweight linearly while in the PNA-based Emax equation, GA was the best covariate for PNA50, and current weight for GFRmax. The final model showed that for a child born at 26 weeks GA, absolute GFR is 18%, 63%, 80%, 92% and 96% of the GFR of a child born at 40 weeks GA at 1 month, 6 months, 1 year, 3 years and 12 years, respectively. PopPK models with the GFR maturation equations predicted concentrations of renally cleared antibiotics across (pre)term-born neonates until 18 years well.

CONCLUSIONS

GFR of preterm individuals catches up with term peers at around three years of age, implying reduced dosages of renally cleared drugs should be considered below this age.

Potentially Harmful Excipients: State of the Art for Oral Liquid Forms Used in Neonatology and Pediatrics Units

The pediatric population exhibits an important age-dependent heterogeneity in pharmacokinetics and pharmacodynamics parameters, resulting in differences in drug efficacy and toxicity compared to the adult population, particularly for neonates. Toxicity and efficacy divergences have been studied for active molecules, but the impact on the pharmacological parameters of excipients remains less well known. To fill this lack of knowledge, several initiatives have been started to gather information on the specific toxicity of excipients, such as the KIDS list or the STEP database. In order to contribute to this much-needed action, in this work, a compilation of the 219 formulations of oral liquid forms prescribed in pediatrics and neonatology units was established based on the summary of product characteristics. Then, for excipients found in more than 10% of the analyzed formulations, a review of their toxicity data was carried out using the STEP database. Finally, for a selection of 10 frequently used liquid forms, the amounts of excipients administered daily were calculated based on the recommended posology in the Summary of Product Characteristics (SPC) and compared with the recommended daily limits proposed by the European Medicine Agency. Pediatrics-adapted formulations are still rare, and it is not always possible to find safe alternatives to drugs containing excipients of interest.

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.

External validation of population pharmacokinetic models of gentamicin in paediatric population from preterm newborns to adolescents

The aim of this study was to externally validate the predictive performance of published population pharmacokinetic models of gentamicin in all paediatric age groups, from preterm newborns to adolescents. We first selected published population pharmacokinetic models of gentamicin developed in the paediatric population with a wide age range. The parameters of the literature models were then re-estimated using the PRIOR subroutine in NONMEM^®. The predictive ability of the literature and the tweaked models was evaluated. Retrospectively collected data from a routine clinical practice (512 concentrations from 308 patients) were used for validation. The models with covariates characterising developmental changes in clearance and volume of distribution had better predictive performance, which improved further after re-estimation. The tweaked model by Wang 2019 performed best, with suitable accuracy and precision across the complete paediatric population. For patients treated in the intensive care unit, a lower proportion of patients would be expected to reach the target trough concentration at standard dosing. The selected model could be used for model-informed precision dosing in clinical settings where the entire paediatric population is treated. However, for use in clinical practice, the next step should include additional analysis of the impact of intensive care treatment on gentamicin pharmacokinetics, followed by prospective validation.

Evaluation of Dosing Guidelines for Gentamicin in Neonates and Children

Although aminoglycosides are frequently prescribed to neonates and children, the ability to reach effective and safe target concentrations with the currently used dosing regimens remains unclear. This study aims to evaluate the target attainment of the currently used dosing regimens for gentamicin in neonates and children. We conducted a retrospective single-center cohort study in neonates and children receiving gentamicin between January 2019 and July 2022, in the Beatrix Children's Hospital. The first gentamicin concentration used for therapeutic drug monitoring was collected for each patient, in conjunction with information on dosing and clinical status. Target trough concentrations were ≤1 mg/L for neonates and ≤0.5 mg/L for children. Target peak concentrations were 8-12 mg/L for neonates and 15-20 mg/L for children. In total, 658 patients were included (335 neonates and 323 children). Trough concentrations were outside the target range in 46.2% and 9.9% of neonates and children, respectively. Peak concentrations were outside the target range in 46.0% and 68.7% of neonates and children, respectively. In children, higher creatinine concentrations were associated with higher gentamicin trough concentrations. This study corroborates earlier observational studies showing that, with a standard dose, drug concentration targets were met in only approximately 50% of the cases. Our findings show that additional parameters are needed to improve target attainment.

New insights in pediatrics in 2021: choices in allergy and immunology, critical care, endocrinology, gastroenterology, genetics, haematology, infectious diseases, neonatology, neurology, nutrition, palliative care, respiratory tract illnesses and telemedicine

In this review, we report the developments across pediatric subspecialties that have been published in the Italian Journal of Pediatrics in 2021. We highlight advances in allergy and immunology, critical care, endocrinology, gastroenterology, genetics, hematology, infectious diseases, neonatology, neurology, nutrition, palliative care, respiratory tract illnesses and telemedicine.

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.

Optimizing gentamicin dosing in different pediatric age groups using population pharmacokinetics and Monte Carlo simulation

Introduction

The use of once daily dosing of aminoglycosides in pediatrics is increasing but studies on dose optimization targeting the pediatric population are limited. This study aimed to derive a population pharmacokinetic model of gentamicin and apply it to design optimal dosing regimens in pediatrics.

Methods

Population pharmacokinetics of gentamicin in pediatrics was described from a retrospective chart review of plasma gentamicin concentration data (peak/ trough levels) of pediatric patients (1 month − 12 years), admitted to non-critically ill pediatrics. Monte Carlo simulations were performed on the resulting pharmacokinetic model to assess the probability of achieving a C_max/MIC target of 10 mg/L over a range of gentamicin MICs of 0.5–2 mg/L and once daily gentamicin dosing regimens. Results: A two-compartment model with additive residual error best described the model with weight incorporated as a significant covariate for both clearance and volume of distribution. Monte Carlo simulations demonstrated a good probability of target attainment even at a MIC of 2 mg/L, where neonates required doses of 6-7 mg/kg/day and older pediatrics required lower daily doses of 4–5 mg/kg/day while maintaining trough gentamicin concentration below the toxicity limit of 1 mg/L. Conclusion: Once daily dosing is a reasonable option in pediatrics that allows target attainment while maintaining trough gentamicin level below the limits of toxicity.

Assessment of the Effects of a High Amikacin Dose on Plasma Peak Concentration in Critically Ill Children

OBJECTIVES

This study aimed to assess the incidence of amikacin plasma peak concentration (C_max) below 60 mg·L^-1 in critically ill children receiving an amikacin dosing regimen of 30 mg kg^-1·day^-1. Secondary objectives were to identify factors associated with low C_max and to assess the incidence of acute kidney injury (AKI).

METHODS

A retrospective observational study was performed in two French pediatric intensive care units. All admitted children who received 30 mg·kg^-1 amikacin and had a C_max measurement were eligible. Clinical and biological data, amikacin dose, and concentrations were collected.

RESULTS

In total, 30 patients were included, aged from 3 weeks to 7 years. They received a median amikacin dosage of 30 mg kg^-1·day^-1 (range 29-33) based on admission body weight (BW), corresponding to 27 mg kg^-1·day^-1 (range 24-30) based on actual BW. C_max was < 60 mg·L^-1 in 21 (70%) children and none had a C_max ≥ 80 mg·L^-1. Among the 15 patients with a measured minimum inhibitory concentration (MIC), 13 (87%) had a C_max/MIC ratio > 8. Univariate analysis showed that factors associated with C_max < 60 mg·L^-1 were high estimated glomerular filtration rate (p = 0.015) and low blood urea concentration (p = 0.001). AKI progression or occurrence was observed after amikacin administration in two (7%) and six (21%) patients, respectively.

CONCLUSIONS

Despite the administration of the maximal recommended amikacin dose, C_max was below the pharmacokinetic target in 70% of our pediatric population. Further studies are needed to develop a pharmacokinetic model in a population of critically ill children to optimize target attainment.

Pharmacokinetics and Target Attainment of Antibiotics in Critically Ill Children: A Systematic Review of Current Literature

BACKGROUND

Pharmacokinetics (PK) are severely altered in critically ill patients due to changes in volume of distribution (Vd) and/or drug clearance (Cl). This affects the target attainment of antibiotics in critically ill children. We aimed to identify gaps in current knowledge and to compare published PK parameters and target attainment of antibiotics in critically ill children to healthy children and critically ill adults.

METHODS

Systematic literature search in PubMed, EMBASE and Web of Science. Articles were labelled as relevant when they included information on PK of antibiotics in critically ill, non-neonatal, pediatric patients. Extracted PK-parameters included Vd, Cl, (trough) concentrations, AUC, probability of target attainment, and elimination half-life.

RESULTS

50 relevant articles were identified. Studies focusing on vancomycin were most prevalent (17/50). Other studies included data on penicillins, cephalosporins, carbapenems and aminoglycosides, but data on ceftriaxone, ceftazidime, penicillin and metronidazole could not be found. Critically ill children generally show a higher Cl and larger Vd than healthy children and critically ill adults. Reduced target-attainment was described in critically ill children for multiple antibiotics, including amoxicillin, piperacillin, cefotaxime, vancomycin, gentamicin, teicoplanin, amikacin and daptomycin. 38/50 articles included information on both Vd and Cl, but a dosing advice was given in only 22 articles.

CONCLUSION

The majority of studies focus on agents where TDM is applied, while other antibiotics lack data altogether. The larger Vd and higher Cl in critically ill children might warrant a higher dose or extended infusions of antibiotics in this patient population to increase target-attainment. Studies frequently fail to provide a dosing advice for this patient population, even if the necessary information is available. Our study shows gaps in current knowledge and encourages future researchers to provide dosing advice for special populations whenever possible.

External Validation of Model-Based Dosing Guidelines for Vancomycin, Gentamicin, and Tobramycin in Critically Ill Neonates and Children: A Pragmatic Two-Center Study

BACKGROUND

The Dutch Pediatric Formulary (DPF) increasingly bases its guidelines on model-based dosing simulations from pharmacokinetic studies. This resulted in nationwide dose changes for vancomycin, gentamicin, and tobramycin in 2015.

OBJECTIVE

We aimed to evaluate target attainment of these altered, model-based doses in critically ill neonates and children.

METHODS

This was a retrospective cohort study in neonatal intensive care unit (NICU) and pediatric ICU (PICU) patients receiving vancomycin, gentamicin, or tobramycin between January 2015 and March 2017 in two university hospitals. The first therapeutic drug monitoring concentration for each patient was collected, as was clinical and dosing information. Vancomycin and tobramycin target trough concentrations were 10-15 and ≤ 1 mg/L, respectively. Target gentamicin trough and peak concentrations were < 1 and 8-12 mg/L, respectively.

RESULTS

In total, 482 patients were included (vancomycin [PICU] n = 62, [NICU] n = 102; gentamicin [NICU] n = 97; tobramycin [NICU] n = 221). Overall, median trough concentrations were within the target range for all cohorts but showed large interindividual variability, causing nontarget attainment. Trough concentrations were outside the target range in 66.1%, 60.8%, 14.7%, and 23.1% of patients in these four cohorts, respectively. Gentamicin peak concentrations were outside the range in 69% of NICU patients (term neonates 87.1%, preterm infants 57.1%). Higher creatinine concentrations were associated with higher vancomycin and tobramycin trough concentrations.

CONCLUSION

This study illustrates the need to validate model-based dosing advice in the real-world setting as both sub- and supratherapeutic concentrations of vancomycin, gentamicin, and tobramycin were very prevalent. Our data underline the necessity for further individualization by addressing the high interindividual variability to improve target attainment.

Population Pharmacokinetic Modeling of Gentamicin in Pediatrics

The primary objective of this work was to characterize the pharmacokinetics (PK) of gentamicin across the whole pediatric age spectrum from premature neonates to young adults with a single model by identifying significant clinical predictors. A nonlinear mixed-effect population PK model was developed with retrospective therapeutic drug-monitoring data. A total of 6459 drug concentration measurements from 3370 hospitalized patients were collected for model building (n = 2357) and evaluation (n = 1013). In agreement with previously reported models, a 2-compartment model with first-order elimination best described the drug PK. Patient-specific factors significantly impacting gentamicin clearance included fat-free mass, postmenstrual age, and serum creatinine (SCr). Based on our model, the deviation of the individual SCr from the age-dependent expected mean SCr value (SCrM) can result in a 40% lower clearance in a patient with renal impairment than that in a patient with normal kidney function, with SCrM:SCr ratios between 0.16 and 3.2 in this study. Consistent with the known age-dependent changes of the proportion of extracellular water in body weight, the inclusion of the impact of extracellular water maturation on the central volume of distribution was found to improve the model fitting significantly. In comparison with other published models, model evaluation suggested the developed model was the least biased and physiologically most representative. These results will be used to inform individualized initial dosing strategies and serve as a prior PK model for Bayesian updating and forecasting as individual clinical observations become available.

A review of population pharmacokinetic models of gentamicin in paediatric patients

WHAT IS KNOWN AND OBJECTIVES

Gentamicin is often used for the treatment of Gram-negative infections. Due to pharmacokinetic variability in paediatric patients, appropriate dosing of gentamicin in the paediatric population is challenging. This article reviews published population pharmacokinetic models of gentamicin in paediatric patients, identifies covariates that significantly influence gentamicin pharmacokinetics, and determines whether there is a consensus on proposed dosing for intravenous gentamicin in this population.

METHODS

The PubMed database was searched for articles published until the end of 2017. If the articles described population pharmacokinetic models of gentamicin in the paediatric population (after intravenous administration of gentamicin), the following data were extracted: type of study, year of publication, population characteristics and number of patients, gentamicin dosing, total number of gentamicin (serum and/or plasma) concentrations, type of population modelling approach, developed model with pharmacokinetic parameters and covariates included.

RESULTS AND DISCUSSION

In most of the studies, one- or two-compartment modelling was applied. The mean estimated gentamicin clearance for newborns, infants and the complete paediatric population was 0.048, 0.13 and 0.067 L/h/kg, respectively, and the mean predicted volume of distribution was 0.475, 0.35 and 0.33 L/kg, respectively. The values reflect differences in body composition and kidney maturation within the different paediatric populations. Gentamicin pharmacokinetics were most influenced by age, body size and renal function.

WHAT IS NEW AND CONCLUSION

Based on our review, the authors agree on a prolonged dosing interval for preterm and term newborns (up to 48 hours). However, there was no agreement on proposed dosing with respect to gestational age. In general, the proposed daily doses were lower compared to those initially applied for preterm newborns and comparable to those for term newborns. For infants and children, the dosing interval remained unchanged (24 hours), but the proposed daily doses were higher than actually applied. When differences in the paediatric population are considered and an appropriate population PK model with applicable covariates is applied, dosing can be individualized. In the future, studies of gentamicin pharmacokinetics in paediatric patients should focus on currently underestimated covariates, such as fat-free mass, concomitantly administered drugs, body temperature and critical illness because these can change gentamicin PK considerably. Consequently, different dosing is required and TDM becomes even more important.

Population Pharmacokinetic Analysis of Gentamicin in Pediatric Extracorporeal Membrane Oxygenation

BACKGROUND

Gentamicin pharmacokinetics may be altered in pediatric patients undergoing extracorporeal membrane oxygenation (ECMO). Description of gentamicin pharmacokinetics and relevant variables can improve dosing.

METHODS

A retrospective population pharmacokinetic study was designed, and pediatric patients who received gentamicin while undergoing ECMO therapy over a period of 6 1/2 years were included. Data collection included the following: patient demographics, serum creatinine, albumin, hematocrit, gentamicin dosing and serum concentrations, urine output, and ECMO circuit parameters. Descriptive statistics were used to characterize the patient population. Population pharmacokinetic analysis was performed with NONMEM, and simulation was performed to identify empiric doses to achieve therapeutic serum concentrations.

RESULTS

A total of 37 patients met study criteria (75.7% male patients), with a median age of 0.17 [interquartile range (IQR) 0.12-0.82] years. Primary indications for ECMO included the following: congenital diaphragmatic hernia (n = 17), persistent pulmonary hypertension (n = 5), and septic shock (n = 4). Patients received a total of 117 gentamicin doses [median 1.8 (IQR 1.4-2.9) mg/kg/dose] and had 125 serum concentrations measured at a median of 22.8 (IQR 15.8-25.5) hours after a dose. Population pharmacokinetic analysis identified a 2-compartment model with additive error as the best fit. Covariates included the following: allometrically scaled fat-free mass on clearance, central and peripheral volume of distribution (VDcentral and VDperipheral), and intercompartmental clearance; serum creatinine on clearance; ultrafiltration rate on central volume of distribution. Simulation identified dosage of 4-5 mg/kg/dose every 24 hours for neonates and infants as an acceptable empiric dosing regimen. Children and adolescents had elevated trough concentrations when dosed according to traditional dosing methods.

CONCLUSIONS

Fat-free mass should be used to dose gentamicin in pediatric ECMO patients. Serum creatinine is a marker of gentamicin clearance and should be used to adjust gentamicin dosing in pediatric ECMO patients.

Optimizing Gentamicin Dosing in Pediatrics Using Monte Carlo Simulations

Gentamicin is known to have concentration-dependent bactericidal activity, and its nephrotoxic effect is well described. We developed a population pharmacokinetic/pharmacodynamic model to optimize gentamicin dosing in pediatrics. Data were retrospectively collected for pediatric patients 1 month to 12 years of age, admitted to general pediatric wards or intensive care units and received gentamicin for suspected or proven Gram-negative infections at King Saud University Medical City, Riyadh, Saudi Arabia. A total of 306 gentamicin peak and trough concentrations sets from 107 patients were analyzed with mean (±standard deviation) patient age and weight of 4.5 ± 3.5 years and 16.7 ± 10.8 kg, respectively. Gentamicin pharmacokinetics were adequately described with a one compartment system (R = 0.82, bias = 1.75% and precision = 88% for population predictions and R = 0.94, bias = 5% and precision = 29% for individual predictions). The gentamicin pharmacokinetic parameters were as follows: volume of distribution = 8.9 L, total body clearance = 2.8 L/h for a 20-kg patient. Monte Carlo simulations showed that doses of 5-6 mg/kg/dose once daily are adequate only to treat infections with Gram-negative organisms having minimal inhibitory concentration less than 1 µg/mL. While, at minimal inhibitory concentration of 1 µg/mL, higher doses (7-8 mg/kg/dose once daily) are needed to maximize the efficacy of gentamicin. However, at minimal inhibitory concentration of 2 µg/mL, even a 10 mg/kg dose showed poor target attainment (52%). The finding of this study highlights the need to reevaluate the current breakpoints of gentamicin and also to assess the safety of higher doses of gentamicin in pediatrics.

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 pharmacokinetic modelling, Monte Carlo simulation and semi-mechanistic pharmacodynamic modelling as tools to personalize gentamicin therapy

Population pharmacokinetic modelling, Monte Carlo simulation and semi-mechanistic pharmacodynamic modelling are all tools that can be applied to personalize gentamicin therapy. This review summarizes and evaluates literature knowledge on the population pharmacokinetics and pharmacodynamics of gentamicin and identifies areas where further research is required to successfully individualize gentamicin therapy using modelling and simulation techniques. Thirty-five studies have developed a population pharmacokinetic model of gentamicin and 15 studies have made dosing recommendations based on Monte Carlo simulation. Variability in gentamicin clearance was most commonly related to renal function in adults and body weight and age in paediatrics. Nine studies have related aminoglycoside exposure indices to clinical outcomes. Most commonly, efficacy has been linked to a Cmax/MIC ≥7-10 and a AUC24/MIC ≥70-100. No study to date has shown a relationship between predicted achievement of exposure targets and actual clinical success. Five studies have developed a semi-mechanistic pharmacokinetic/pharmacodynamic model to predict bacteria killing and regrowth following gentamicin exposure and one study has developed a deterministic model of aminoglycoside nephrotoxicity. More complex semi-mechanistic models are required that consider the immune response, use of multiple antibiotics, the severity of illness, and both efficacy and toxicity. As our understanding grows, dosing of gentamicin based on sound pharmacokinetic/pharmacodynamic principles should be applied more commonly in clinical practice.

A Population Pharmacokinetic Model of Gentamicin in Pediatric Oncology Patients To Facilitate Personalized Dosing

To ensure the safe and effective dosing of gentamicin in children, therapeutic drug monitoring (TDM) is recommended. TDM utilizing Bayesian forecasting software is recommended but is unavailable, as no population model that describes the pharmacokinetics of gentamicin in pediatric oncology patients exists. This study aimed to develop and externally evaluate a population pharmacokinetic model of gentamicin to support personalized dosing in pediatric oncology patients. A nonlinear mixed-effect population pharmacokinetic model was developed from retrospective data. Data were collected from 423 patients for model building and a further 52 patients for external evaluation. A two-compartment model with first-order elimination best described the gentamicin disposition. The final model included renal function (described by fat-free mass and postmenstrual age) and the serum creatinine concentration as covariates influencing gentamicin clearance (CL). Final parameter estimates were as follow CL, 5.77 liters/h/70 kg; central volume of distribution, 21.6 liters/70 kg; peripheral volume of distribution, 13.8 liters/70 kg; and intercompartmental clearance, 0.62 liter/h/70 kg. External evaluation suggested that current models developed in other pediatric cohorts may not be suitable for use in pediatric oncology patients, as they showed a tendency to overpredict the observations in this population. The final model developed in this study displayed good predictive performance during external evaluation (root mean square error, 46.0%; mean relative prediction error, -3.40%) and may therefore be useful for the personalization of gentamicin dosing in this cohort. Further investigations should focus on evaluating the clinical application of this model.

Scaling clearance in paediatric pharmacokinetics: All models are wrong, which are useful?

Linked Articles

This article is commented on in the editorial by Holford NHG and Anderson BJ. Why standards are useful for predicting doses. Br J Clin Pharmacol 2017; 83: 685–7. doi: 10.1111/bcp.13230

Aim

When different models for weight and age are used in paediatric pharmacokinetic studies it is difficult to compare parameters between studies or perform model‐based meta‐analyses. This study aimed to compare published models with the proposed standard model (allometric weight^0.75 and sigmoidal maturation function).

Methods

A systematic literature search was undertaken to identify published clearance (CL) reports for gentamicin and midazolam and all published models for scaling clearance in children. Each model was fitted to the CL values for gentamicin and midazolam, and the results compared with the standard model (allometric weight exponent of 0.75, along with a sigmoidal maturation function estimating the time in weeks of postmenstrual age to reach half the mature value and a shape parameter). For comparison, we also looked at allometric size models with no age effect, the influence of estimating the allometric exponent in the standard model and, for gentamicin, using a fixed allometric exponent of 0.632 as per a study on glomerular filtration rate maturation. Akaike information criteria (AIC) and visual predictive checks were used for evaluation.

Results

No model gave an improved AIC in all age groups, but one model for gentamicin and three models for midazolam gave slightly improved global AIC fits albeit using more parameters: AIC drop (number of parameters), –4.1 (5), –9.2 (4), –10.8 (5) and –10.1 (5), respectively. The 95% confidence interval of estimated CL for all top performing models overlapped.

Conclusion

No evidence to reject the standard model was found; given the benefits of standardised parameterisation, its use should therefore be recommended.

Clinical Pharmacology Studies in Critically Ill Children

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

Population Pharmacokinetics of Gentamicin in Mexican Children With Severe Malnutrition

BACKGROUND

To develop a population pharmacokinetic model of gentamicin in children with complicated severe malnutrition and to study the influence of covariates (weight and age) on pharmacokinetic indices. In addition, we use the model to perform Monte Carlo simulations to explore the efficacy of several dosage regimens.

METHODS

Twenty-six children with severe complicated malnutrition were studied. Ninety-six samples of gentamicin plasma concentrations, obtained from 0.5 to 8 hours after intravenous dosing, were analyzed. Population pharmacokinetic models were built using the program Monolix 4.2 (Lixoft, Antony, France). Monte Carlo simulations were performed to evaluate optimal dosage regimens, using the final pharmacokinetic model, based on the probability of pharmacokinetic-pharmacodynamic target attainment.

RESULTS

The concentration-time data were fitted best to 1-compartment model. The estimated population clearance was 1.1 L/h, and the volume of distribution was 2.23 L, with an interindividual variability of 47.2% and 35.6%, respectively. The final models for the clearance and volume of distribution were as follows: CL (L/h) = CL = 1.15 (age/median age) and V (L) = 2.33 (weight/median weight). In Monte Carlo simulations, gentamicin given in dosages of 7.5 to 15 mg/kg optical density was effective in achieving the pharmacodynamic target Cmax:minimal inhibitory concentration >10 for minimal inhibitory concentrations ≤2.5 mg/L, with a probability lower than 1% for Cmin >1 mg/L.

CONCLUSIONS

Based on the available evidence, an intravenous dose of 7.5 to 15 mg/kg once daily in children with complicated severe malnutrition and normal renal function ensures high probability of efficacy and low risk of nephrotoxicity, which gives further support to the recommendations issued by the World Health Organization treatment for this patient population.

Development and Evaluation of a Gentamicin Pharmacokinetic Model That Facilitates Opportunistic Gentamicin Therapeutic Drug Monitoring in Neonates and Infants

Trough gentamicin therapeutic drug monitoring (TDM) is time-consuming, disruptive to neonatal clinical care, and a patient safety issue. Bayesian models could allow TDM to be performed opportunistically at the time of routine blood tests. This study aimed to develop and prospectively evaluate a new gentamicin model and a novel Bayesian computer tool (neoGent) for TDM use in neonatal intensive care. We also evaluated model performance for predicting peak concentrations and the area under the concentration-time curve from time 0 h to time t h (AUC0- t). A pharmacokinetic meta-analysis was performed on pooled data from three studies (1,325 concentrations from 205 patients). A 3-compartment model was used with the following covariates: allometric weight scaling, postmenstrual and postnatal age, and serum creatinine concentration. Final parameter estimates (standard errors) were as follows: clearance, 6.2 (0.3) liters/h/70 kg of body weight; central volume (V), 26.5 (0.6) liters/70 kg; intercompartmental disposition (Q), 2.2 (0.3) liters/h/70 kg; peripheral volume V2, 21.2 (1.5) liters/70 kg; intercompartmental disposition (Q2), 0.3 (0.05) liters/h/70 kg; peripheral volume V3, 148 (52.0) liters/70 kg. The model's ability to predict trough concentrations from an opportunistic sample was evaluated in a prospective observational cohort study that included data from 163 patients and 483 concentrations collected in five hospitals. Unbiased trough predictions were obtained; the median (95% confidence interval [CI]) prediction error was 0.0004 (-1.07, 0.84) mg/liter. Results also showed that peaks and AUC0- t values could be predicted (from one randomly selected sample) with little bias but relative imprecision, with median (95% CI) prediction errors being 0.16 (-4.76, 5.01) mg/liter and 10.8 (-24.9, 62.2) mg · h/liter, respectively. neoGent was implemented in R/NONMEM and in the freely available TDMx software.

Pharmacometric Approaches to Personalize Use of Primarily Renally Eliminated Antibiotics in Preterm and Term Neonates

Sepsis remains a major cause of mortality and morbidity in neonates, and, as a consequence, antibiotics are the most frequently prescribed drugs in this vulnerable patient population. Growth and dynamic maturation processes during the first weeks of life result in large inter- and intrasubject variability in the pharmacokinetics (PK) and pharmacodynamics (PD) of antibiotics. In this review we (1) summarize the available population PK data and models for primarily renally eliminated antibiotics, (2) discuss quantitative approaches to account for effects of growth and maturation processes on drug exposure and response, (3) evaluate current dose recommendations, and (4) identify opportunities to further optimize and personalize dosing strategies of these antibiotics in preterm and term neonates. Although population PK models have been developed for several of these drugs, exposure-response relationships of primarily renally eliminated antibiotics in these fragile infants are not well understood, monitoring strategies remain inconsistent, and consensus on optimal, personalized dosing of these drugs in these patients is absent. Tailored PK/PD studies and models are useful to better understand relationships between drug exposures and microbiological or clinical outcomes. Pharmacometric modeling and simulation approaches facilitate quantitative evaluation and optimization of treatment strategies. National and international collaborations and platforms are essential to standardize and harmonize not only studies and models but also monitoring and dosing strategies. Simple bedside decision tools assist clinical pharmacologists and neonatologists in their efforts to fine-tune and personalize the use of primarily renally eliminated antibiotics in term and preterm neonates.

Population pharmacokinetic study of gentamicin in a large cohort of premature and term neonates

AIM

This study aims to investigate the clinical and demographic factors influencing gentamicin pharmacokinetics in a large cohort of unselected premature and term newborns and to evaluate optimal regimens in this population.

METHODS

All gentamicin concentration data, along with clinical and demographic characteristics, were retrieved from medical charts in a Neonatal Intensive Care Unit over 5 years within the frame of a routine therapeutic drug monitoring programme. Data were described using non-linear mixed-effects regression analysis ( nonmem®).

RESULTS

A total of 3039 gentamicin concentrations collected in 994 preterm and 455 term newborns were included in the analysis. A two compartment model best characterized gentamicin disposition. The average parameter estimates, for a median body weight of 2170 g, were clearance (CL) 0.089 l h(-1) (CV 28%), central volume of distribution (Vc ) 0.908 l (CV 18%), intercompartmental clearance (Q) 0.157 l h(-1) and peripheral volume of distribution (Vp ) 0.560 l. Body weight, gestational age and post-natal age positively influenced CL. Dopamine co-administration had a significant negative effect on CL, whereas the influence of indomethacin and furosemide was not significant. Both body weight and gestational age significantly influenced Vc . Model-based simulations confirmed that, compared with term neonates, preterm infants need higher doses, superior to 4 mg kg(-1) , at extended intervals to achieve adequate concentrations.

CONCLUSIONS

This observational study conducted in a large cohort of newborns confirms the importance of body weight and gestational age for dosage adjustment. The model will serve to set up dosing recommendations and elaborate a Bayesian tool for dosage individualization based on concentration monitoring.

Dose derivation of once-daily dosing guidelines for gentamicin in critically ill pediatric patients

OBJECTIVES

To determine dose and eligibility criteria for once-daily dosing (ODD) of gentamicin in critically ill pediatric patients.

METHODS

Retrospective chart review of patients admitted to the Pediatric Intensive Care Unit or Cardiac Critical Care Unit at The Hospital for Sick Children (SickKids) who received traditionally dosed intravenous (IV) gentamicin (January 2008 to June 2010). Statistically significant patient characteristics associated with gentamicin pharmacokinetic (PK) parameters were determined by multiple linear regression. Binary partitioning was used to set critical values for these characteristics to derive dose for ODD of gentamicin. Feasibility of implementing ODD of gentamicin in critically ill children was assessed using individualized PK parameters to simulate area under the concentration-time curves and drug-free intervals while targeting a maximum concentration (C(max)) of 16-20 mg/L. Eligibility criteria were determined by patient characteristics that had a statistically significant impact on gentamicin PK.

RESULTS

Volume of distribution (V(d)) and elimination rate constant (k(e)) were calculated for 140 patients. Weight and admission unit were significantly associated with weight-normalized V(d) (Vd/kg), whereas age and serum creatinine (SCr) were significantly associated with k(e). Weight <5 kg and SCr ≥20% over age-specific upper normal limit before gentamicin initiation were associated with prolonged gentamicin elimination. Gentamicin 6 mg/kg IV every 24 hours, the dose at which the highest percentage of patients achieved C(max), area under the curve, and drug-free interval within target ranges simultaneously, was selected as the proposed ODD regimen.

CONCLUSIONS

A regimen of gentamicin 6 mg/kg IV every 24 hours for Pediatric Intensive Care Unit/Cardiac Critical Care Unit patients at SickKids weighing ≥5 kg with SCr <20% above age-specific upper normal limit before initiation of gentamicin is proposed.

Optimized antimicrobial dosing strategies: a survey of pediatric hospitals

BACKGROUND

Extended-interval aminoglycoside (EIAG) and extended- and continuous-infusion β-lactam (EIBL and CIBL) dosing strategies are increasingly used in adults, but pediatric literature is limited.

OBJECTIVE

The objective of this study was to describe the use of EIAG, EIBL, and CIBL dosing in pediatric hospitals in the USA.

STUDY DESIGN, SETTING, AND PARTICIPANTS

A national survey of children's hospitals was conducted. A single practitioner from each target hospital was identified through the Children's Hospital Association. Practice-based survey questions identified whether hospitals utilize EIAG, EIBL, and CIBL dosing.

MAIN OUTCOME MEASURE

The main outcome measure was the percentage utilization of the dosing strategies, with secondary outcomes being the reasons for not using these dosing strategies.

RESULTS

Seventy-seven of 215 identified practitioners (36 %) participated in the survey. EIAG, EIBL, and CIBL dosing were utilized in 63 %, 24 %, and 13 % of responding hospitals, respectively. The most common reasons for not using EIAG were concern regarding lack of efficacy data (56 %) and concern regarding the duration of the drug-free period (41 %). Respondents who did not utilize EIBL cited concern due to lack of pediatric EIBL efficacy data (54 %), the need for more intravenous access (54 %), intravenous medication compatibility issues (39 %), and the time during which the patient is attached to an intravenous infusion (31 %).

CONCLUSION

This survey of children's hospitals indicates that EIAG is used in over 50 % of hospitals, but there is some lag in adoption of EIBL and CIBL dosing, both of which are used in fewer than 25 % of hospitals. Additional studies may provide much-needed evidence to increase the utilization of these strategies.

Predictive performance of gentamicin dosing nomograms

Background

Several nomograms have been proposed to facilitate the determination of initial gentamicin dosing regimens in clinical settings. This study aimed to assess the predictive performance of these nomograms in Korean patients.

Methods

Gentamicin concentrations were determined in 84 patients with infective endocarditis (IE) and in 95 patients with other infections. All patients underwent therapeutic drug monitoring in Seoul National University Hospital from 2006 to 2012. Individual pharmacokinetic parameters were estimated using a Bayesian method, which predicted steady state peak and trough serum concentrations. Six nomograms were evaluated in patients with “other” infections: the Thomson guidelines, Hull-Sarubbi table, and Rule of Eights, for multiple daily dosing; and the Hartford nomogram, Barnes-Jewish Hospital nomogram, and Sanford Guide, for extended-interval dosing. In IE patients, synergistic combination dosing nomograms, based on the American Heart Association dosing interval guidelines, were evaluated.

Results

Gentamicin dosing nomograms performed poorly in attaining the target peak serum concentrations. Multiple-daily dosing nomograms predicted peak serum gentamicin concentrations better than did the extended-interval dosing nomograms (31.9%–72.3% vs 4.3%–45.7%, respectively). Similarly, in patients with IE, the once-daily dosing nomogram resulted in a significantly lower percentage of patients achieving target peak gentamicin concentrations than that associated with the thrice-daily dosing nomogram (P=0.0015). All of the multiple-daily dosing, extended-interval dosing, and synergistic combination dosing nomograms predicted the nontoxic target trough concentrations in >80% of patients.

Conclusion

Gentamicin dosing nomograms performed poorly in achieving the target peak serum concentrations. New gentamicin nomograms may be required in patients with IE, particularly for once-daily dosing. Therapeutic drug monitoring is highly recommended for gentamicin to ensure that the target concentrations are achieved.

Simultaneous pharmacokinetic modeling of gentamicin, tobramycin and vancomycin clearance from neonates to adults: towards a semi-physiological function for maturation in glomerular filtration

PURPOSE

Since glomerular filtration rate (GFR) is responsible for the elimination of a large number of water-soluble drugs, the aim of this study was to develop a semi-physiological function for GFR maturation from neonates to adults.

METHODS

In the pharmacokinetic analysis (NONMEM VI) based on data of gentamicin, tobramycin and vancomycin collected in 1,760 patients (age 1 day-18 years, bodyweight 415 g-85 kg), a distinction was made between drug-specific and system-specific information. Since the maturational model for clearance is considered to contain system-specific information on the developmental changes in GFR, one GFR maturational function was derived for all three drugs.

RESULTS

Simultaneous analysis of these three drugs showed that maturation of GFR mediated clearance from preterm neonates to adults was best described by a bodyweight-dependent exponent (BDE) function with an exponent varying from 1.4 in neonates to 1.0 in adults (ClGFR = Cldrug*(BW/4 kg)(BDE) with BDE = 2.23*BW(-0.065)). Population clearance values (Cldrug) for gentamicin, tobramycin and vancomycin were 0.21, 0.28 and 0.39 L/h for a full term neonate of 4 kg, respectively.

DISCUSSION

Based on an integrated analysis of gentamicin, tobramycin and vancomycin, a semi-physiological function for GFR mediated clearance was derived that can potentially be used to establish evidence based dosing regimens of renally excreted drugs in children.

A pharmacokinetic standard for babies and adults

The pharmacokinetic behavior of medicines used in humans follows largely predictable patterns across the human age range from premature babies to elderly adults. Most of the differences associated with age are in fact due to differences in size. Additional considerations are required to describe the processes of maturation of clearance processes and postnatal changes in body composition. Application of standard approaches to reporting pharmacokinetic parameters is essential for comparative human pharmacokinetic studies from babies to adults. A standardized comparison of pharmacokinetic parameters obtained in children and adults is shown for 46 drugs. Appropriate size scaling shows that children (over 2 years old) are similar to adults. Maturation changes are generally completed within the first 2 years of postnatal life; consequently babies may be considered as immature children, whereas children are just small adults.

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.