Piperacillin Population Pharmacokinetics and Dosing Regimen Optimization in Critically Ill Children with Normal and Augmented Renal Clearance

Individualised amoxicillin-clavulanate dosing recommendations for critically ill children with augmented clearance after cardiac surgery

OBJECTIVE

Children who undergo cardiac surgery are prone to postoperative infections for which amoxicillin-clavulanate is a cornerstone antibiotic. Nevertheless, amoxicillin-clavulanate pharmacokinetics have not been studied in infants and children after cardiac surgery so far. Antibiotic exposure might be highly variable in this population due to the impact of growth, maturation, and specific pathophysiological and surgery-induced alterations. The objective of this study was to develop evidence-based amoxicillin-clavulanate dosing recommendations based on population pharmacokinetic analysis and probability of target attainment simulations in children after cardiac surgery.

METHODS

Critically ill children (aged 1 day to 15 y) who underwent cardiac surgery and who were treated postoperatively with amoxicillin-clavulanate (30-60 mg/kg/6 h based on the amoxicillin component, infused in 30 min) were included. Up to five amoxicillin and clavulanate blood samples were collected per dose at predefined sampling times. Population pharmacokinetics analysis was performed using nonlinear mixed effects modelling software NONMEM.

RESULTS

We collected 316 amoxicillin and 287 clavulanate blood samples from 37 patients. A three-compartment model for amoxicillin and a two-compartment model for clavulanate best described pharmacokinetics, with allometric weight scaling and maturation functions added a priori to scale for size and age. Clearance estimates were remarkably high, except in patients receiving vasopressors, which decreased clearance of amoxicillin-clavulanate by a third. Using a pharmacokinetic/pharmacodynamic target of 50%fT>MIC of 8 mg/L, patients not on vasopressors warranted 4-hourly dosing to achieve adequate drug exposure due to augmented amoxicillin clearance. Only in patients treated with vasopressors was the standard 6-hourly dosing regimen sufficient to attain amoxicillin concentrations above the MIC for half of the dosing interval.

CONCLUSIONS

Current amoxicillin-clavulanate dosing regimens for critically ill children after cardiac surgery need to be updated to avoid subtherapeutic concentrations and clinical failure due to augmented clearance (ClinicalTrials.gov NCT02456974).

Model-informed dose optimization for prophylactic piperacillin-tazobactam in perioperative pediatric critically ill patients

Piperacillin/tazobactam (PTZ) is frequently prescribed during the perioperative period as prophylaxis in critically ill patients. Current international guidelines recommend that the pediatric intraoperative dosing regimen for PTZ be 90-112.5 mg/kg (80-100 mg/kg as piperacillin [PIP]) administered every 2 hours (Q2H). Concerns have been raised not only about the risk of nephrotoxicity due to elevated PIP exposure but also regarding the practicality of adhering to a 2-h dosing interval in clinical settings. To address these concerns, we employed population pharmacokinetic (PK) modeling and simulation approaches to optimize PTZ dosing regimens in pediatric intraoperative patients. PIP plasma concentration data were obtained from 34 patients using an opportunistic sampling strategy. A two-compartment model was found to adequately describe the PK data. Creatinine clearance was identified as a significant covariate on clearance. The inclusion of inter-occasion variability significantly improved model fit. Simulations across body weights of 10-70 kg and creatinine clearance of 20-130 mL/min/1.73 m2 demonstrated that 6-15 mg/kg Q2H, or a 10 mg/kg loading dose followed by 1.0-2.75 mg/kg/h continuous infusion would achieve free PIP concentrations being above the minimum inhibitory concentration (MIC) for 100% of the dosing interval (100% fT >1× MIC). For achieving 100% fT >4× MIC, 25-55 mg/kg Q2H or a 20 mg/kg loading dose followed by 3.25-9.25 mg/kg/h continuous infusion was derived. The model-informed simulations indicated that both lower Q2H doses and continuous infusion methods are clinically viable options and potentially resolve current clinical challenges during intraoperative dosing.

Population Pharmacokinetics and Dose Optimization of Piperacillin in Infants and Children with Pneumonia

OBJECTIVE

We aimed to determine the piperacillin disposition and optimize the dosing regimens for infants and children with pneumonia.

METHODS

An opportunistic sampling strategy was used in this pharmacokinetic study. High-performance liquid chromatography was used to measure the concentrations of piperacillin in plasma samples. A population pharmacokinetic model was conducted using NONMEM.

RESULTS

The pharmacokinetic data of 90 samples from 64 infants and children with pneumonia (age range: 0.09-1.72 years for infants and 2.12-11.10 years for children) were available. A two-compartment model with first-order elimination was the most suitable model to describe the population pharmacokinetics of piperacillin. A covariate analysis indicated that body weight and age were significant factors affecting clearance. Monte Carlo simulations showed that a 50-mg/kg every 8 h or every 12 h dosing regimen results in underdosing. Results both in infants and children showed that an extended infusion (3 h) of various dosing regimens (80, 100, or 130 mg/kg) three times daily or a 300-mg/kg continuous infusion can reach a therapeutic level based on the chosen target for the probability of target attainment threshold of 70%, 80%, and 90% at minimum inhibitory concentration breakpoints of 8 mg/L and 16 mg/L.

CONCLUSIONS

A population pharmacokinetic model was obtained to evaluate the disposition of piperacillin, and the optimal dosing regimens were provided for use in infants and children with pneumonia.

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.

Evaluation of knowledge and attitude concerning augmented renal clearance among physicians and clinical pharmacists in Al-Ain, UAE: A cross-sectional study

BACKGROUND

Kidney function assessment is crucial in critical illness patients and is required before administering renally excreted medication, especially antibiotics and antiepileptics. Conventional clinical practice often focuses on renal impairment with low creatinine clearance (CrCl) and overlooks the augmented renal clearance (ARC), which is defined by (CrCl) more than 130 ml/min. This typical demonstration neglects individuals who experience hyperfunctioning kidneys. Among critically ill patients, the prevalence of (ARC) is approximately 20% to 65% of cases. This study aims to evaluate physicians' and clinical pharmacists' knowledge about ARC-associated risk factors, antibiotic regimen modification in ARC patients, and attitudes towards ARC workshops and guidelines in Al-Ain, UAE.

METHODS

A cross-sectional, online self-administered survey-based study was designed to achieve this study's aim. The questionnaire was constructed on profound literature analysis, validated, and piloted. The survey was emailed to physicians and pharmacists working in two hospitals, private and governmental, and distributed through different social media platforms over three months, December 2022-February 2023.

RESULTS

Of the 92 complete responses (32 clinical pharmacists, 60 physicians), 57 (61.9%), were aware of ARC, but 72 (78%) demonstrated poor knowledge overall. Clinical pharmacists had a higher mean rank of knowledge than the physician's group. Meanwhile, 70 (76.1%) participants were unaware of the eGFR threshold to determine ARC. There is a noticeable positive attitude toward seeking more information about antibiotic dose adjustment in ARC patients at 85 (92%) of the respondents. Remarkably, only 28 (30.4%) were directly involved with ARC patients' treatment plans.

CONCLUSION

In conclusion, clinical pharmacists showed better knowledge than physicians. However, overall, the participating healthcare providers lacked knowledge about ARC, so a reliable source of information regarding ARC should be utilized. Future research could explore the implementation of professional development workshops for healthcare providers and national guidelines and then assess their impact on patient outcomes.

Dose optimization of β-lactam antibiotics in children: from population pharmacokinetics to individualized therapy

INTRODUCTION

β-Lactams are the most widely used antibiotics in children. Their optimal dosing is essential to maximize their efficacy, while minimizing the risk for toxicity and the further emergence of antimicrobial resistance. However, most β-lactams were developed and licensed long before regulatory changes mandated pharmacokinetic studies in children. As a result, pediatric dosing practices are poorly harmonized and off-label use remains common today.

AREAS COVERED

β-Lactam pharmacokinetics and dose optimization strategies in pediatrics, including fixed dose regimens, therapeutic drug monitoring, and model-informed precision dosing are reviewed.

EXPERT OPINION/COMMENTARY

Standard pediatric doses can result in subtherapeutic exposure and non-target attainment for specific patient subpopulations (neonates, critically ill children, e.g.). Such patients could benefit greatly from more individualized approaches to dose optimization, beyond a relatively simple dose adaptation based on weight, age, or renal function. In this context, Therapeutic Drug Monitoring (TDM) and Model-Informed Precision Dosing (MIPD) emerge as particularly promising avenues. Obstacles to their implementation include the lack of strong evidence of clinical benefit due to the paucity of randomized clinical trials, of standardized assays for monitoring concentrations, or of adequate markers for renal function. The development of precision medicine tools is urgently needed to individualize therapy in vulnerable pediatric subpopulations.

Defining the pharmacokinetic/pharmacodynamic index of piperacillin/tazobactam within a hollow-fibre infection model to determine target attainment in intensive care patients

Background

It is important to optimize dosing schemes of antibiotics to maximize the probability of therapeutic success. The recommended pharmacokinetic/pharmacodynamic (PK/PD) index for piperacillin/tazobactam therapy in clinical studies ranges widely (50%-100% fT>1-4×MIC). Dosing schemes failing to achieve PK/PD targets may lead to negative treatment outcomes.

Objectives

The first aim of this study was to define the optimal PK/PD index of piperacillin/tazobactam with a hollow-fibre infection model (HFIM). The second aim was to predict whether these PK/PD targets are currently achieved in critically ill patients through PK/PD model simulation.

Patients and methods

A dose-fractionation study comprising 21 HFIM experiments was performed against a range of Gram-negative bacterial pathogens, doses and infusion times. Clinical data and dose histories from a case series of nine patients with a known bacterial infection treated with piperacillin/tazobactam in the ICU were collected. The PK/PD index and predicted plasma concentrations and therefore target attainment of the patients were simulated using R version 4.2.1.

Results

fT >MIC was found to be the best-fitting PK/PD index for piperacillin/tazobactam. Bactericidal activity with 2 log10 cfu reduction was associated with 77% fT>MIC. Piperacillin/tazobactam therapy was defined as clinically 'ineffective' in ∼78% (7/9) patients. Around seventy-one percent (5/7) of these patients had a probability of >10% that 2  log10 cfu reduction was not attained.

Conclusions

Our dose-fractionation study indicates an optimal PK/PD target in piperacillin/tazobactam therapies should be 77% fT>MIC for 2 log10 kill. Doses to achieve this target should be considered when treating patients in ICU.

A descriptive pharmacokinetic/pharmacodynamic analysis of ceftazidime-avibactam in a case series of critically ill patients with augmented renal clearance

To describe the pharmacokinetics/pharmacodynamics (PK/PD) of a 2 h infusion of ceftazidime-avibactam (CAZ-AVI) in critically ill patients with augmented renal clearance (ARC). A retrospective review of all critically ill patients with ARC who were treated with CAZ-AVI between August 2020 and May 2023 was conducted. Patients whose 12-h creatinine clearance prior to CAZ-AVI treatment and steady-state concentration (Css) of CAZ-AVI were both monitored were enrolled. The free fraction (fCss) of CAZ-AVI was calculated from Css. The joint PK/PD targets of CAZ-AVI were considered optimal when a Css/minimum inhibitory concentration (MIC) ratio for CAZ ≥4 (equivalent to 100% fT > 4 MIC) and a Css/CT ratio of AVI >1 (equivalent to 100% fT > CT 4.0 mg/L) were reached simultaneously, quasioptimal when only one of the two targets was reached, and suboptimal when neither target was reached. The relationship between PK/PD goal achievement, microbial eradication and the clinical efficacy of CAZ-AVI was evaluated. Four patients were included. Only one patient achieved optimal joint PK/PD targets, while the other three reached suboptimal targets. The patient with optimal PK/PD targets achieved microbiological eradication, while the other three patients did not, but all four patients achieved good clinical efficacy. Standard dosages may not enable most critically ill patients with ARC to reach the optimal joint PK/PD targets of CAZ-AVI. Optimal drug dose adjustment of CAZ-AVI in ARC patients requires dynamic drug concentration monitoring.

Personalized application of antimicrobial drugs in pediatric patients with augmented renal clearance: a review of literature

The effect of renal functional status on drug metabolism is a crucial consideration for clinicians when determining the appropriate dosage of medications to administer. In critically ill patients, there is often a significant increase in renal function, which leads to enhanced drug metabolism and potentially inadequate drug exposure. This phenomenon, known as augmented renal clearance (ARC), is commonly observed in pediatric critical care settings. The findings of the current study underscore the significant impact of ARC on the pharmacokinetics and pharmacodynamics of antimicrobial drugs in critically ill pediatric patients. Moreover, the study reveals a negative correlation between increased creatinine clearance and blood concentrations of antimicrobial drugs. The article provides a comprehensive review of ARC screening in pediatric patients, including its definition, risk factors, and clinical outcomes. Furthermore, it summarizes the dosages and dosing regimens of commonly used antibacterial and antiviral drugs for pediatric patients with ARC, and recommendations are made for dose and infusion considerations and the role of therapeutic drug monitoring.

CONCLUSION

 ARC impacts antimicrobial drugs in pediatric patients.

WHAT IS KNOWN

• ARC is inextricably linked to the failure of antimicrobial therapy, recurrence of infection, and subtherapeutic concentrations of drugs.

WHAT IS NEW

• This study provides an updated overview of the influence of ARC on medication use and clinical outcomes in pediatric patients. • In this context, there are several recommendations for using antibiotics in pediatric patients with ARC: 1) increase the dose administered; 2) prolonged or continuous infusion administration; 3) use of TDM; and 4) use alternative drugs that do not undergo renal elimination.

International consensus recommendations for the use of prolonged-infusion beta-lactam antibiotics: Endorsed by the American College of Clinical Pharmacy, British Society for Antimicrobial Chemotherapy, Cystic Fibrosis Foundation, European Society of Clinical Microbiology and Infectious Diseases, Infectious Diseases Society of America, Society of Critical Care Medicine, and Society of Infectious Diseases Pharmacists

Intravenous β-lactam antibiotics remain a cornerstone in the management of bacterial infections due to their broad spectrum of activity and excellent tolerability. β-lactams are well established to display time-dependent bactericidal activity, where reductions in bacterial burden are directly associated with the time that free drug concentrations remain above the minimum inhibitory concentration (MIC) of the pathogen during the dosing interval. In an effort to take advantage of these bactericidal characteristics, prolonged (extended and continuous) infusions (PIs) can be applied during the administration of intravenous β-lactams to increase time above the MIC. PI dosing regimens have been implemented worldwide, but implementation is inconsistent. We report consensus therapeutic recommendations for the use of PI β-lactams developed by an expert international panel with representation from clinical pharmacy and medicine. This consensus guideline provides recommendations regarding pharmacokinetic and pharmacodynamic targets, therapeutic drug-monitoring considerations, and the use of PI β-lactam therapy in the following patient populations: severely ill and nonseverely ill adult patients, pediatric patients, and obese patients. These recommendations provide the first consensus guidance for the use of β-lactam therapy administered as PIs and have been reviewed and endorsed by the American College of Clinical Pharmacy (ACCP), the British Society for Antimicrobial Chemotherapy (BSAC), the Cystic Fibrosis Foundation (CFF), the European Society of Clinical Microbiology and Infectious Diseases (ESCMID), the Infectious Diseases Society of America (IDSA), the Society of Critical Care Medicine (SCCM), and the Society of Infectious Diseases Pharmacists (SIDP).

Individualized antibiotic dosage regimens for patients with augmented renal clearance

Objectives: Augmented renal clearance (ARC) is a state of enhanced renal function commonly observed in 30%-65% of critically ill patients despite normal serum creatinine levels. Using unadjusted standard dosing regimens of renally eliminated drugs in ARC patients often leads to subtherapeutic concentrations, poor clinical outcomes, and the emergence of multidrug-resistant bacteria. We summarized pharmaceutical, pharmacokinetic, and pharmacodynamic research on the definition, underlying mechanisms, and risk factors of ARC to guide individualized dosing of antibiotics and various strategies for optimizing outcomes. Methods: We searched for articles between 2010 and 2022 in the MEDLINE database about ARC patients and antibiotics and further provided individualized antibiotic dosage regimens for patients with ARC. Results: 25 antibiotic dosage regimens for patients with ARC and various strategies for optimization of outcomes, such as extended infusion time, continuous infusion, increased dosage, and combination regimens, were summarized according to previous research. Conclusion: ARC patients, especially critically ill patients, need to make individualized adjustments to antibiotics, including dose, frequency, and method of administration. Further comprehensive research is required to determine ARC staging, expand the range of recommended antibiotics, and establish individualized dosing guidelines for ARC patients.

Beta-lactam exposure and safety in intermittent or continuous infusion in critically ill children: an observational monocenter study

The aim of this study was to assess the pharmacokinetic (PK) exposure and clinical toxicity for three beta-lactams: cefotaxime, piperacillin/tazobactam, and meropenem, depending on two lengths of infusion: continuous and intermittent, in critically ill children. This single center observational prospective study was conducted in a pediatric intensive care unit. All hospitalized children who had one measured plasma concentration of the investigated antibiotics were included. Plasma antibiotic concentrations were interpreted by a pharmacologist, using a Bayesian approach based on previously published population pharmacokinetic models in critically ill children. Exposure was considered optimal, low, or high according to the PK target 100% fT_{> 4 × MIC} and a trough concentration below the toxic concentration (50 mg.L^-1 for cefotaxime, 150 mg.L^-1 for piperacillin, and 44 mg.L^-1 for meropenem). Between May 2019 and January 2020, 80 patients were included and received 106 antibiotic courses: 74 (70%) were administered in intermittent infusion (II) and 32 (30%) in continuous infusion (CI). Compared to II, CI provided more optimal PK exposure (n = 22/32, 69% for CI versus n = 35/74, 47% for II, OR 1.2, 95%CI 1.01-1.5, p = 0.04), less underexposure (n = 4/32, 13% for CI versus n = 36/74, 49% for II, OR 0.7, 95%CI 0.6-0.84, p < 0.001), and more overexposure (n = 6/32, 19% for CI versus n = 3/74, 4% for II, OR 1.2, 95%CI 1.03-1.3, p = 0.01). Five adverse events have been reported during the study period, although none has been attributed to beta-lactam treatment.

CONCLUSION

CI provided a higher probability to attain an optimal PK target compared to II, but also a higher risk for overexposure. Regular therapeutic drug monitoring is recommended in critically ill children receiving beta-lactams, regardless of the length of infusion.

WHAT IS KNOWN

• Since beta-lactams are time-dependent antibiotics, the probability to attain the pharmacokinetic target is higher with continuous infusion compared to that with intermittent infusion. • In daily practice, continuous or extended infusions are rarely used despite recent guidelines, and toxicity is hardly reported.

WHAT IS NEW

• Continuous infusion provided a higher probability to attain an optimal pharmacokinetic target compared to intermittent infusion, but also a higher risk of overexposure. • Regular therapeutic drug monitoring is recommended in critically ill children receiving beta-lactams, regardless of the length of infusion.

Relationship between piperacillin concentrations, clinical factors and piperacillin/tazobactam-associated acute kidney injury

BACKGROUND

Piperacillin/tazobactam, a commonly used antibiotic, is associated with acute kidney injury (AKI). The relationship between piperacillin concentrations and AKI remains unknown.

OBJECTIVE

Estimate piperacillin exposures in critically ill children and young adults administered piperacillin/tazobactam to identify concentrations and clinical factors associated with piperacillin-associated AKI.

PATIENTS AND METHODS

We assessed piperacillin pharmacokinetics in 107 patients admitted to the paediatric ICU who received at least one dose of piperacillin/tazobactam. Piperacillin AUC, highest peak (Cmax) and highest trough (Cmin) in the first 24 hours of therapy were estimated. Piperacillin-associated AKI was defined as Kidney Disease: Improving Global Outcomes (KDIGO) Stage 2/3 AKI present >24 hours after initial piperacillin/tazobactam dose. Likelihood of piperacillin-associated AKI was rated using the Naranjo Adverse Drug Reaction Probability Scale. Multivariable logistic regression was performed to identify patient and clinical predictors of piperacillin-associated AKI.

RESULTS

Out of 107 patients, 16 (15%) were rated as possibly or probably having piperacillin-associated AKI. Estimated AUC and highest Cmin in the first 24 hours were higher in patients with piperacillin-associated AKI (2042 versus 1445 mg*h/L, P = 0.03; 50.1 versus 10.7 mg/L, P < 0.001). Logistic regression showed predictors of piperacillin-associated AKI included higher Cmin (OR: 5.4, 95% CI: 1.7-23) and age (OR: 1.13, 95% CI: 1.05-1.25).

CONCLUSIONS

We show a relationship between estimated piperacillin AUC and highest Cmin in the first 24 hours of piperacillin/tazobactam therapy and piperacillin-associated AKI, suggesting total piperacillin exposure early in the course is associated with AKI development. These data could serve as the foundation for implementation of model-informed precision dosing to reduce AKI incidence in patients given piperacillin/tazobactam.

β-lactam precision dosing in critically ill children: Current state and knowledge gaps

There has been emerging interest in implementing therapeutic drug monitoring and model-informed precision dosing of β-lactam antibiotics in critically ill patients, including children. Despite a position paper endorsed by multiple international societies that support these efforts in critically ill adults, implementation of β-lactam precision dosing has not been widely adopted. In this review, we highlight what is known about β-lactam antibiotic pharmacokinetics and pharmacodynamics in critically ill children. We also define the knowledge gaps that present barriers to acceptance and implementation of precision dosing of β-lactam antibiotics in critically ill children: a lack of consensus on which subpopulations would benefit most from precision dosing and the uncertainty of how precision dosing changes outcomes. We conclude with opportunities for further research to close these knowledge gaps.

Dose optimization of β-lactams antibiotics in pediatrics and adults: A systematic review

Background: β-lactams remain the cornerstone of the empirical therapy to treat various bacterial infections. This systematic review aimed to analyze the data describing the dosing regimen of β-lactams. Methods: Systematic scientific and grey literature was performed in accordance with Preferred Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. The studies were retrieved and screened on the basis of pre-defined exclusion and inclusion criteria. The cohort studies, randomized controlled trials (RCT) and case reports that reported the dosing schedule of β-lactams are included in this study. Results: A total of 52 studies met the inclusion criteria, of which 40 were cohort studies, 2 were case reports and 10 were RCTs. The majority of the studies (34/52) studied the pharmacokinetic (PK) parameters of a drug. A total of 20 studies proposed dosing schedule in pediatrics while 32 studies proposed dosing regimen among adults. Piperacillin (12/52) and Meropenem (11/52) were the most commonly used β-lactams used in hospitalized patients. As per available evidence, continuous infusion is considered as the most appropriate mode of administration to optimize the safety and efficacy of the treatment and improve the clinical outcomes. Conclusion: Appropriate antibiotic therapy is challenging due to pathophysiological changes among different age groups. The optimization of pharmacokinetic/pharmacodynamic parameters is useful to support alternative dosing regimens such as an increase in dosing interval, continuous infusion, and increased bolus doses.

Suboptimal Beta-Lactam Therapy in Critically Ill Children: Risk Factors and Outcome

OBJECTIVES

In critically ill children, severely altered pharmacokinetics may result in subtherapeutic β-lactam antibiotic concentrations when standard pediatric dosing regimens are applied. However, it remains unclear how to recognize patients most at risk for suboptimal exposure and their outcome. This study aimed to: 1) describe target attainment for β-lactam antibiotics in critically ill children, 2) identify risk factors for suboptimal exposure, and 3) study the association between target nonattainment and clinical outcome.

DESIGN

Post hoc analysis of the "Antibiotic Dosing in Pediatric Intensive Care" study (NCT02456974, 2012-2019). Steady-state trough plasma concentrations were classified as therapeutic if greater than or equal to the minimum inhibitory concentration of the (suspected) pathogen. Factors associated with subtherapeutic concentrations and clinical outcome were identified by logistic regression analysis.

SETTING

The pediatric and cardiac surgery ICU of a Belgian tertiary-care hospital.

PATIENTS

One hundred fifty-seven patients (aged 1 mo to 15 yr) treated intravenously with amoxicillin-clavulanic acid, piperacillin-tazobactam, or meropenem.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Three hundred eighty-two trough concentrations were obtained from 157 patients (median age, 1.25 yr; interquartile range, 0.4-4.2 yr). Subtherapeutic concentrations were measured in 39 of 60 (65%), 43 of 48 (90%), and 35 of 49 (71%) of patients treated with amoxicillin-clavulanic acid, piperacillin-tazobactam, and meropenem, respectively. Estimates of glomerular filtration rate (eGFR; 54% increase in odds for each sd increase in value, 95% CI, 0.287-0.736; p = 0.001) and the absence of vasopressor treatment (2.8-fold greater odds, 95% CI, 1.079-7.253; p = 0.034) were independently associated with target nonattainment. We failed to identify an association between antibiotic concentrations and clinical failure.

CONCLUSIONS

Subtherapeutic β-lactam concentrations are common in critically ill children and correlate with renal function. eGFR equations may be helpful in identifying patients who may require higher dosing. Future studies should focus on the impact of subtherapeutic concentrations on clinical outcome.

Therapeutic Drug Monitoring of Antibiotics in Critically Ill Children: An Observational Study in a Pediatric Intensive Care Unit

BACKGROUND

Septic critically ill children are at a high risk of inadequate antibiotic exposure, requiring them to undergo therapeutic drug monitoring (TDM). The aim of this study was to describe the use of TDM for antibiotics in critically ill children.

METHODS

The authors conducted a single-center observational study between June and December 2019, with all children treated with antibiotics in a pediatric intensive care unit located in a French university hospital. Standard clinical and laboratory data were recorded. Blood samples were collected for routine laboratory tests, and plasma antibiotic levels were assayed using validated analytical methods.

RESULTS

A total of 209 children received antibiotics. TDM was performed in 58 patients (27.8%) who had a greater mean organ dysfunction (according to the International Pediatric Sepsis Consensus Conference) (3 versus 1 in the non-TDM group; P < 0.05) and were treated with antibiotics for longer. A total of 208 samples were analyzed. The median [interquartile range] assay turnaround time was 3 (1-5) days, and 48 (46.2%) of the 104 initial antibiotic concentration values were below the pharmacokinetic/pharmacodynamic targets. A total of 34 (46%) of the 74 off-target TDM measurements available before the end of the antibiotic treatment prompted dose adjustment. This dose adjustment increased the proportion of on-target TDM measurements (70% versus 20% without adjustment). Subsequent measurements of the minimum inhibitory concentration showed that the use of the European Committee on Antimicrobial Susceptibility Testing's epidemiological cutoff values led to underestimation of pharmacokinetic/pharmacodynamic target attainment in 10 cases (20%).

CONCLUSIONS

TDM seems to be an effective means of optimizing antibiotic exposure in critically ill children. This requires timely plasma antibiotic assays and minimum inhibitory concentration measurements. It is important to define which patients should undergo TDM and how this monitoring should be managed.

Estimation of cefepime, piperacillin, and tazobactam clearance with iohexol-based glomerular filtration rate in paediatric patients

PURPOSE

Estimated glomerular filtration rate (eGFR) equations reflect kidney function imprecisely. We aimed to describe whether iohexol-based GFR or eGFRs predict clearance of cefepime, piperacillin, and tazobactam in pharmacokinetic (PK) models in this population and its clinical significance.

METHODS

Hospitalized patients (0.5-25 years) with haemato-oncological disease and infection receiving cefepime or piperacillin/tazobactam were included. PK samples were collected at a steady state concomitantly with samples for iohexol-based GFR. PK models were developed in NONMEM. Weight, postmenstrual age, iohexol-based GFR, different eGFR equations (Schwartz updated, Lund-Malmö revised, CKD-EPI, Bouvet, Schwartz cystatin C-based) were tested as covariates. Probabilities of neurotoxic/therapeutic concentrations were assessed by simulations.

RESULTS

Fifteen patients receiving cefepime and 17 piperacillin/tazobactam were included (median (range) age 16.2 (1.9-26.0) and 10.5 (0.8-25.6) years, iohexol-based GFR 102 (68-140) and 116 (74-137) mL/min/1.73 m², respectively). Two-compartment model provided the best fit for all drugs. Weight was covariate for central and peripheral compartment, clearance and intercompartmental clearance (only tazobactam), and postmenstrual age for clearance (excluding cefepime). Iohexol-based GFR was the best predictor of clearance. The model of cefepime without vs with iohexol-based GFR underestimated the probability of neurotoxic concentrations (28.3-28.6% vs 52.1-69.3%) and overestimated the probability of therapeutic concentrations (> 90% vs 81.9-87.1%) in the case of iohexol-based GFR 70-80 and 130-140 mL/min/1.73 m², respectively.

CONCLUSION

Iohexol-based GFR can predict better than eGFRs the clearance of cefepime, piperacillin, and tazobactam in children and young adults with haemato-oncological disease and infection, warranting further investigation as an indicator of renal function to improve targeting of therapeutic window.

TRIAL REGISTRATION NUMBER AND DATE OF REGISTRATION

EudraCT 2015-000,631-32, EudraCT 2016-003,374-40 (24.10.2016).

Beta-Lactams Therapeutic Monitoring in Septic Children-What Target Are We Aiming for? A Scoping Review

The antimicrobial therapy of sepsis and septic shock should be individualized based on pharmacokinetic/pharmacodynamic (PK/PD) parameters to deliver effective and timely treatment of life-threatening infections. We conducted a literature scoping review to identify therapeutic targets of beta-lactam antibiotics in septic pediatric patients and the strategies that have been applied to overcome sepsis-related altered pharmacokinetics and increase target attainment against susceptible pathogens. A systematic search was conducted in the MEDLINE, EMBASE and Web of Science databases to select studies conducted since 2010 with therapeutic monitoring data of beta-lactams in septic children. Last searches were performed on 02 September 2021. Two independent authors selected the studies and extracted the data. A narrative and qualitative approach was used to summarize the findings. Out of the 118 identified articles, 21 met the eligibility criteria. Population pharmacokinetic modeling was performed in 12 studies, while nine studies reported data from bedside monitoring of beta-lactams. Most studies were conducted in the United States of America (n = 9) and France (n = 5) and reported PK/PD data of amoxicillin, ampicillin, azlocillin, aztreonam, cefazolin, cefepime, cefotaxime, ceftaroline, ceftazidime, doripenem, meropenem and piperacillin/tazobactam. Therapeutic targets ranged from to 40% fT> MIC to 100% fT> 6 × MIC. Prolonging the infusion time and frequency were most described strategies to increase target attainment. Monitoring beta-lactam serum concentrations in clinical practice may potentially maximize therapeutic target attainment. Further studies are required to define the therapeutic target associated with the best clinical outcomes.

Pharmacokinetics of Commonly Used Medications in Children Receiving Continuous Renal Replacement Therapy: A Systematic Review of Current Literature

BACKGROUND AND OBJECTIVE

The use of continuous renal replacement therapy (CRRT) for renal support has increased substantially in critically ill children compared with intermittent modalities owing to its preferential effects on hemodynamic stability. With the expanding role of CRRT, the quantification of extracorporeal clearance and the effect on primary pharmacokinetic parameters is of the utmost importance. Within this review, we aimed to summarize the current state of the literature and compare published pharmacokinetic analyses of commonly used medications in children receiving CRRT to those who are not.

METHODS

A systematic search of the literature within electronic databases PubMed, EMBASE, Cochrane Library, and Web of Science was conducted. Published studies that were included contained relevant information on the use of commonly administered medications to children, from neonates to adolescents, receiving CRRT. Pharmacokinetic parameters that were analyzed included volume of distribution, total clearance, extracorporeal clearance, area under the curve, and elimination half-life. Information regarding CRRT circuit, flow rates, and membrane components was analyzed to investigate differences in pharmacokinetics between each modality.

RESULTS

Forty-five studies met the final inclusion criteria within this systematic review, totaling 833 pediatric patients, with 586 receiving CRRT. Antimicrobials were the most common pharmacological class represented within the literature, representing 81% (35/43) of studies analyzed. Children receiving CRRT largely had similar volume of distribution and total clearance to critically ill children not receiving CRRT, suggesting reno-protective dose adjustments may lead to subtherapeutic dosing regimens in these patients. Overall, there was a tendency for hydrophilic agents, with a low protein binding to undergo elevated total clearance in these children. However, results should be interpreted with caution because of the large variability amongst patient populations and heterogeneity with CRRT modalities, flow rates, and use of extracorporeal membrane oxygenation within studies. This review was able to identify that variation in solute removal, or CRRT modalities, properties (i.e., flow rates), and membrane composition, may have differing effects on the pharmacokinetics of commonly administered medications.

CONCLUSIONS

The current state of the literature regarding medications administered to children receiving CRRT largely focuses on antimicrobials. Significant gaps remain with other commonly used medications such as sedatives and analgesics. Overall reporting of patient clinical characteristics, CRRT settings, and circuit composition was poor, with only 10% of articles including all relevant information to assess the impact of CRRT on total clearance. Changes in pharmacokinetics because of CRRT often required higher than labeled doses, suggesting renally adjusted or reno-protective doses may lead to subtherapeutic dosing regimens. A thorough understanding of the interplay between patient, drug, and CRRT-circuit factors are required to ensure adequate delivery of dosing regimens to this vulnerable population.

Pharmacokinetic/Pharmacodynamic Optimization of Hospital-Acquired and Ventilator-Associated Pneumonia: Challenges and Strategies

Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) are correlated with high mortality rates worldwide. Thus, the administration of antibiotic therapy with appropriate dosing regimen is critical. An efficient antibiotic is needed to maintain an adequate concentration at the infection site, for a sufficient period of time, to achieve the best therapeutic outcome. It can, however, be challenging for antibiotics to penetrate the pulmonary system due to the complexity of its structure. Crossing the blood alveolar barrier is a difficult process determined by multiple factors that are either drug related or infection related. Thus, the understanding of pharmacokinetics/pharmacodynamics (PK/PD) of antibiotics identifies the optimum dosing regimens to achieve drug penetration into the epithelial lining fluid at adequate therapeutic concentrations. Critically ill patients in the ICU can express augmented renal clearance (ARC), characterized by enhanced renal function, or may have renal dysfunction necessitating supportive care such as continuous renal replacement therapy (CRRT). Both ARC and CRRT can alter drug elimination, thus affecting drug concentrations. PK of critically ill patients is less clear due to the multiple variabilities associated with their condition. Therefore, conventional dosing regimens often lead to therapeutic failure. Another major hurdle faced in optimizing treatment for HAP/VAP is the reduction of the in vitro potency. Therapeutic drug monitoring (TDM), if available, may allow health care providers to personalize treatment to maximize efficacy of the drug exposures while minimizing toxicity. TDM can be of significant importance in populations whom PK are less defined and for resistant infections to achieve the best therapeutic outcome.

Antibiotics in critically ill children-a narrative review on different aspects of a rational approach

Especially critically ill children are exposed to antibiotic overtreatment, mainly caused by the fear of missing out a severe bacterial infection. Potential adverse effects and selection of multi-drug resistant bacteria play minor roles in decision making. This narrative review first describes harm from antibiotics and second focuses on different aspects that could help to reduce antibiotic overtreatment without harming the patient: harm from antibiotic treatment, diagnostic approaches, role of biomarkers, timing of antibiotic therapy, empiric therapy, targeted therapy, and therapeutic drug monitoring. Wherever possible, we linked the described evidence to the current Surviving Sepsis Campaign guidelines. Antibiotic stewardship programs should help guiding antibiotic therapy for critically ill children. IMPACT: Critically ill children can be harmed by inadequate or overuse of antibiotics. Hemodynamically unstable children with a suspicion of infection should be immediately treated with broad-spectrum antibiotics. In contrast, in hemodynamically stable children with sepsis and organ dysfunction, a time frame of 3 h for proper diagnostics may be adequate before starting antibiotics if necessary. Less and more targeted antibiotic treatment can be achieved via antibiotic stewardship programs.

Continuous infusion of piperacillin-tazobactam significantly improves target attainment in children with cancer and fever

Background

Children with febrile neutropenia commonly exhibit alterations of pharmacokinetic (PK) parameters, leading to decreased β‐lactam concentrations.

Aims

This study evaluated piperacillin PK and probability of target attainment (PTA) with continuous infusion of piperacillin‐tazobactam, in order to optimize the dosing regimen.

Methods

This prospective PK study included children with cancer, aged 1–17 years, who were treated with piperacillin‐tazobactam for suspected or verified infection. A piperacillin‐tazobactam loading dose (100 mg/kg) was administered followed by continuous infusion (300 mg/kg/day). The unbound fraction of piperacillin was quantified by high‐performance liquid chromatography and PK were described using population PK modeling. PK data was used to update and extend a previous PK model built on data following intermittent administration. Monte Carlo simulations were performed to assess PTA for targets of 100% time above the minimum inhibitory concentration (100% fT > MIC) and 50% fT > 4xMIC.

Results

We included 68 fever episodes among 38 children with a median (IQR) age of 6.5 years and body weight of 27.4 kg (15.1–54.0). A three‐compartment model adequately described the concentration‐time data. Median (95% confidence interval) estimates for clearance and piperacillin concentration at steady state were 14.2 L/h/70 kg (13.0; 15.3) and 47.6 mg/L (17.2; 129.5), respectively. Body weight or lean body weight was significantly associated with the PK parameters, and body weight was integrated in the final PK model. Based on piperacillin exposure, continuous infusion was the only dosing regimen to achieve optimal PTA for the P. aeruginosa breakpoint (16 mg/L) with the target of 100% fT > MIC, and a daily dose of 300 mg/kg reached optimal PTA. The strict target of 50% fT > 4xMIC (64 mg/L) was not feasibly attained by any dosing regimen at recommended doses.

Conclusion

Unlike conventional piperacillin intermittent administration and extended infusion regimens, continuous infusion allows the target of 100% fT > MIC to be reached for children with febrile neutropenia.

Scoping review of augmented renal clearance in critically ill pediatric patients

Augmented renal clearance (ARC), a phenomenon of enhanced elimination of renal solutes, has been described in adult critically ill patients, but little is known about the phenomenon in children. The aim of this scoping review was to gather and summarize all evidence on ARC in pediatric patients to examine its breadth and depth including prevalence, risk factors, and pharmacokinetic alterations and identify any gaps for further areas of inquiry. PubMed, Embase, and Web of Science were searched for titles, abstracts, or keywords that focused on ARC. Non-English studies, reviews, and nonhuman studies were excluded. Reporting followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses for Scoping Reviews (PRISMA-ScR) guidelines. Data were extracted on article type, study details, patient population, ARC definition and prevalence, methods of renal function assessment, and study results. A total of 215 citations were found with 25 citations meeting the criteria for inclusion in pediatrics (2102 total patients); the majority of studies (84%) focused on pharmacokinetics (PK) of antimicrobial agents. The median/mean age range was 1.25-12 years. There were a total of 10 different definitions of ARC. The prevalence of ARC ranged from 7.8% to 78%. The most common method for documenting creatinine clearance (CrCl) was the modified Schwartz equation (64%). Only 20% of studies reported risk factors for ARC including low serum creatinine, increasing age, febrile neutropenia, male, septic shock, and treatment with antibiotics. Glycopeptide antimicrobials were the most evaluated class (42.9%) among the 21 antimicrobial drug studies. All studies reported increased drug clearance and/or poor probability of achieving target concentrations of the agents studied. ARC showed variable prevalence in pediatric patients likely due to the lack of a standard definition and many studies not considering age-related changes in CrCl with pediatric intensive care unit (PICU) patients. ARC was shown to impact PK of antibiotics commonly administered to pediatric patients, which may necessitate changes in standard dosing regimens.

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.

Individualized precision dosing approaches to optimize antimicrobial therapy in pediatric populations

Introduction:Severe infections continue to impose a major burden on critically ill children and mortality rates remain stagnant. Outcomes rely on accurate and timely delivery of antimicrobials achieving target concentrations in infected tissue. Yet, developmental aspects, disease-related variables, and host factors may severely alter antimicrobial pharmacokinetics in pediatrics. The emergence of antimicrobial resistance increases the need for improved treatment approaches.Areas covered:This narrative review explores why optimization of antimicrobial therapy in neonates, infants, children, and adolescents is crucial and summarizes the possible dosing approaches to achieve antimicrobial individualization. Finally, we outline a roadmap toward scientific evidence informing the development and implementation of precision antimicrobial dosing in critically ill children.The literature search was conducted on PubMed using the following keywords: neonate, infant, child, adolescent, pediatrics, antimicrobial, pharmacokinetic, pharmacodynamic target, Bayes dosing software, optimizing, individualizing, personalizing, precision dosing, drug monitoring, validation, attainment, and software implementation. Further articles were sought from the references of the above searched articles.Expert opinion:Recently, technological innovations have emerged that enabled the development of individualized antimicrobial dosing approaches in adults. More work is required in pediatrics to make individualized antimicrobial dosing approaches widely operationalized in this population.

Population pharmacokinetics of intravenous and oral ciprofloxacin in children to optimize dosing regimens

PURPOSE

This study aimed to characterize pharmacokinetics of intravenous and oral ciprofloxacin in children to optimize dosing scheme.

METHODS

Children treated with ciprofloxacin were included. Pharmacokinetics were described using non-linear mixed-effect modelling and validated with an external dataset. Monte Carlo simulations investigated dosing regimens to achieve a target AUC_0-24 h/MIC ratio ≥ 125.

RESULTS

A total of 189 children (492 concentrations) were included. A two-compartment model with first-order absorption and elimination best described the data. An allometric model was used to describe bodyweight (BW) influence, and effects of estimated glomerular filtration rate (eGFR) and age were significant on ciprofloxacin clearance.

CONCLUSION

The recommended IV dose of 10 mg/kg q8h, not exceeding 400 mg q8h, would achieve AUC_0-24 h to successfully treat bacteria with MICs ≤ 0.25 (e.g. Salmonella, Escherichia coli, Proteus, Haemophilus, Enterobacter, and Klebsiella). A dose increase to 600 mg q8h in children > 40 kg and to 15 mg/kg q8h (max 400 mg q8h, max 600 mg q8h if augmented renal clearance, i.e., eGFR > 200 mL/min/1.73 m²) in children < 40 kg would be needed for the strains with highest MIC (16% of Pseudomonas aeruginosa and 47% of Staphylococcus aureus). The oral recommended dose of 20 mg/kg q12h (not exceeding 750 mg) would cover bacteria with MICs ≤ 0.125 but may be insufficient for bacteria with higher MIC and a dose increase according bodyweight and eGFR would be needed. These doses should be prospectively confirmed, and a therapeutic drug monitoring could be used to refine them individually.

Current Ceftriaxone Dose Recommendations are Adequate for Most Critically Ill Children: Results of a Population Pharmacokinetic Modeling and Simulation Study

Background and Objective

Ceftriaxone is a cornerstone antibiotic for critically ill children with severe infections. Despite its widespread use, information on the pharmacokinetics of ceftriaxone is lacking in this population. We aimed to determine ceftriaxone pharmacokinetics in critically ill children and to propose ceftriaxone dosing guidelines resulting in adequate target attainment using population pharmacokinetic modeling and simulation.

Methods

Critically ill children (aged 0–18 years) treated with intravenous ceftriaxone (100 mg/kg once daily, infused in 30 minutes) and a central or arterial line in place were eligible. Opportunistic blood sampling for total and unbound ceftriaxone concentrations was used. Population pharmacokinetic analysis was performed using non-linear mixed-effects modeling on NONMEM™ Version 7.4.3. Simulations were performed to select optimal doses using probability of target attainment for two pharmacokinetic targets of the minimum inhibitory concentration (MIC) reflecting the susceptibility of pathogens (f T > MIC 100% and fT > 4 × MIC 100%).

Results

Two hundred and five samples for total and 43 time-matched samples for unbound plasma ceftriaxone concentrations were collected from 45 patients, median age 2.5 (range 0.1–16.7) years. A two-compartment model with bodyweight as the co-variate for volume of distribution and clearance, and creatinine-based estimated glomerular filtration rate as an additional covariate for clearance, best described ceftriaxone pharmacokinetics. For a typical patient (2.5 years, 14 kg) with an estimated glomerular filtration rate of 80 mL/min/1.73 m², the current 100-mg/kg once-daily dose results in a probability of target attainment of 96.8% and 60.8% for a MIC of 0.5 mg/L and 4 × MIC (2 mg/L), respectively, when using fT > MIC 100% as a target. For a 50-mg/kg twice-daily regimen, the probability of target attainment was 99.9% and 93.4%, respectively.

Conclusions

The current dosing regimen of ceftriaxone provides adequate exposure for susceptible pathogens in most critically ill children. In patients with an estimated glomerular filtration rate of > 80 mL/min/1.73 m² or in areas with a high prevalence of less-susceptible pathogens (MIC ≥ 0.5 mg/L), a twice-daily dosing regimen of 50 mg/kg can be considered to improve target attainment.

Clinical Trial Registration

POPSICLE study (ClinicalTrials.gov, NCT03248349, registered 14 August, 2017), PERFORM study (ClinicalTrials.gov, NCT03502993, registered 19 April, 2018).

Supplementary Information

The online version contains supplementary material available at 10.1007/s40262-021-01035-9.

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.

Piperacillin-Tazobactam in Intensive Care Units: A Review of Population Pharmacokinetic Analyses

Piperacillin-tazobactam is a potent β-lactam/β-lactamase inhibitor antibiotic commonly prescribed in the intensive care unit setting. Admitted patients often show large variability in treatment response due to multiple pathophysiological changes present in this population that alter the drug's pharmacokinetics. This review summarizes the population pharmacokinetic models developed for piperacillin-tazobactam and provides comprehensive data on current dosing strategies while identifying significant covariates in critically ill patients. A literature search on the PubMed database was conducted, from its inception to July 2020. Relevant articles were retained if they met the defined inclusion/exclusion criteria. A total of ten studies, published between 2009 and 2020, were eligible. One- and two-compartment models were used in two and eight studies, respectively. The lowest estimated piperacillin clearance value was 3.12 L/h, and the highest value was 19.9 L/h. The estimations for volume of distribution varied between 11.2 and 41.2 L. Tazobactam clearance values ranged between 5.1 and 6.78 L/h, and tazobactam volume of distribution values ranged between 17.5 and 76.1 L. The most frequent covariates were creatinine clearance and body weight, each present in four studies. Almost all studies used an exponential approach for the interindividual variability. The highest variability was observed in piperacillin central volume of distribution, at a value of 75.0%. Simulations showed that continuous or extended infusion methods performed better than intermittent administration to achieve appropriate pharmacodynamic targets. This review synthesizes important pharmacokinetic elements for piperacillin-tazobactam in an intensive care unit setting. This will help clinicians better understand changes in the drug's pharmacokinetic parameters in this specific population.

Optimizing Aminoglycoside Dosing Regimens for Critically Ill Pediatric Patients with Augmented Renal Clearance: a Convergence of Parametric and Nonparametric Population Approaches

Augmented renal clearance (ARC) can occur in critically ill pediatric patients receiving aminoglycosides such as gentamicin and tobramycin, yet optimal dosing strategies for ARC are undefined. We evaluated the probability of achieving efficacious or toxic exposures in pediatrics. Parallel population modeling of concentration strategies were pursued using Pmetrics v1.5.2 (nonparametric) and Monolix v2019R2 (parametric). Bayesian exposures were used to classify ARC based on total clearance (CL). The effects of serum creatinine (SCR), creatinine clearance (CRCL), total body weight (TBW), postnatal age (PNA), and ARC were explored as covariates. The probabilities of target attainment (PTA) (i.e., maximum concentration [C _max]/MIC, area under the concentration-time curve [AUC]/MIC) and of toxic exposure (PTE) (i.e., minimum concentration [C _min] > 2 μg/ml) were calculated according to PNA and ARC. A total of 123 patients (1 to 21 years old, 56% female) contributed 304 concentrations. A two-compartment model was superior to a one-compartment model in both approaches. Bayesian posterior predicted concentrations from the nonparametric base model fit the data well (R ² = 0.96) and classified 34 patients as having ARC (28%). Both the nonparametric and parametric approaches resulted in allometrically scaling of TBW on volume (V) and clearance (CL). ARC modified CL and central V. CRCL and a maturation function modified CL. ARC was associated with a 1.49- versus 1.66-fold increase in CL and a 1.56- versus 1.66-fold increase in the central V (nonparametric versus parametric). A high dose of 12 mg/kg of body weight/day was required to achieve adequate PTA when MICs were 1 to 2 μg/ml; ARC lowered achievable MICs. When PNA was <2 years, PTE was increased. Aminoglycoside monotherapy should be avoided in critically ill pediatric patients with ARC when MICs exceed 1 μg/ml, as optimal exposures are unachievable with standard dosing.

Population Pharmacokinetic Study of Cefathiamidine in Infants With Augmented Renal Clearance

Objectives: Augmented renal clearance (ARC) of primarily renally eliminated antibacterial agents may result in subtherapeutic antibiotic concentrations and, as a consequence, worse clinical outcomes. Cefathiamidine is frequently used as empirical antimicrobial therapy in children with ARC, but pharmacokinetic studies in infants are lacking. This population pharmacokinetic study in infants with ARC was conducted to determine optimal dosing regimens of cefathiamidine.

Methods: The population pharmacokinetics was conducted in 20 infants treated with cefathiamidine. Plasma samples of cefathiamidine were collected using opportunistic sampling, and the concentrations were detected by UPLC-MS/MS. Data analysis was performed to determine pharmacokinetic parameters and to characterize pharmacokinetic variability of cefathiamidine using nonlinear mixed effects modelling (NONMEM) software program.

Results: The data (n = 36) from 20 infants (age range, 0.35–1.86 years) with ARC were fitted best with a 1-compartment model. Allometrically scaled weight and age as significant covariates influenced cefathiamidine pharmacokinetics. The median (range) values of estimated clearance and the volume of distribution were 0.22 (0.09–0.29) L/h/kg and 0.34 (0.24–0.41) L/kg, respectively. Monte Carlo simulations showed that the cefathiamidine doses of 100 mg/kg/day q12 h, 50 mg/kg/day q8 h and 75 mg/kg/day q6 h were chosen for bacteria with MIC 0.25, 0.5 and 2 mg/L, respectively.

Conclusion: The population pharmacokinetic model of cefathiamidine for infants with ARC was developed. The PTA - based dosing regimens were recommended based on the final model.

External Evaluation of Vancomycin Population Pharmacokinetic Models at Two Clinical Centers

Background: Numerous vancomycin population pharmacokinetic models in neonates have been published; however, their predictive performances remain unknown. This study aims to evaluate their external predictability and explore the factors that might affect model performance. Methods: Published population pharmacokinetic models in neonates were identified from the literature and evaluated using datasets from two clinical centers, including 171 neonates with a total of 319 measurements of vancomycin levels. Predictive performance was assessed by prediction- and simulation-based diagnostics and Bayesian forecasting. Furthermore, the effect of model structure and a number of identified covariates was also investigated. Results: Eighteen published pharmacokinetic models of vancomycin were identified after a systematic literature search. Using prediction-based diagnostics, no model had a median prediction error of ≤ ± 15%, a median absolute prediction error of ≤30%, and a percentage of prediction error that fell within ±30% of >50%. A simulation-based visual predictive check of most models showed there were large deviations between observations and simulations. After Bayesian forecasting with one or two prior observations, the predicted performance improved significantly. Weight, age, and serum creatinine were identified as the most important covariates. Moreover, employing a maturation model based on weight and age as well as nonlinear model to incorporate serum creatinine level significantly improved predictive performance. Conclusion: The predictability of the pharmacokinetic models for vancomycin is closely related to the approach used for modeling covariates. Bayesian forecasting can significantly improve the predictive performance of models.

Key Challenges in Providing Effective Antibiotic Therapy for Critically Ill Patients with Bacterial Sepsis and Septic Shock

Early initiation of effective antibiotic therapy is vitally important for saving the lives of critically ill patients with sepsis or septic shock. The susceptibility of the infecting pathogen and the ability of the selected dosage regimen to safely achieve the required antibiotic exposure need to be carefully considered to achieve a high probability of a successful outcome. Critically ill patients commonly experience substantial pathophysiological changes that impact the functions of various organs, including the kidneys. Many antibiotics are predominantly renally eliminated and thus renal function is a major determinant of the regimen needed to achieve the required antibiotic exposure. However, currently, there is a paucity of guidelines to inform antibiotic dosing in critically ill patients, including those with sepsis or septic shock. This paper briefly reviews methods that are commonly used in critically ill patients to provide a measure of renal function, and approaches that describe the relationship between the exposure to an antibiotic and its antibacterial effects. Two common conditions that very substantially complicate the use of antibiotics in critically ill patients with sepsis, unstable renal function, and augmented renal clearance, are considered in detail and their potential therapeutic implications are explored. Suggestions are provided on how treatment of bacterial infections in critically ill patients with sepsis might be improved. Of high potential are model-informed approaches that aim to individualize initial treatment regimens based on patient and bacterial characteristics, with refinement of regimens during treatment in response to monitoring antibiotic concentrations, responsive measures of renal function, and other important clinical data.

Optimizing the Use of Antibiotic Agents in the Pediatric Intensive Care Unit: A Narrative Review

Antibiotics are one of the most prescribed drug classes in the pediatric intensive care unit, yet the incidence of inappropriate antibiotic prescribing remains high in critically ill children. Optimizing the use of antibiotics in this population is imperative to guarantee adequate treatment, avoid toxicity and the occurrence of antibiotic resistance, both on a patient level and on a population level. Antibiotic stewardship encompasses all initiatives to promote responsible antibiotic usage and the PICU represents a major target environment for antibiotic stewardship programs. This narrative review provides a summary of the available knowledge on the optimal selection, duration, dosage, and route of administration of antibiotic treatment in critically ill children. Overall, more scientific evidence on how to optimize antibiotic treatment is warranted in this population. We also give our personal expert opinion on research priorities.

A New Framework to Implement Model-Informed Dosing in Clinical Guidelines: Piperacillin and Amikacin as Proof of Concept

Background: Modeling and simulation is increasingly used to study pediatric pharmacokinetics, but clinical implementation of age-appropriate doses lags behind. Therefore, we aimed to develop model-informed doses using published pharmacokinetic data and a decision framework to adjust dosing guidelines based on these doses, using piperacillin and amikacin in critically ill children as proof of concept.

Methods: Piperacillin and amikacin pharmacokinetic models in critically ill children were extracted from literature. Concentration-time profiles were simulated for various dosing regimens for a virtual PICU patient dataset, including the current DPF dose and doses proposed in the studied publications. Probability of target attainment (PTA) was compared between the different dosing regimens. Next, updated dosing recommendations for the DPF were proposed, and evaluated using a new framework based on PK study quality and benefit-risk analysis of clinical implementation.

Results: Three studies for piperacillin (critically ill children) and one for amikacin (critically ill pediatric burn patients) were included. Simulated concentration-time profiles were performed for a virtual dataset of 307 critically ill pediatric patients, age range 0.1–17.9 y. PTA for unbound piperacillin trough concentrations >16 mg/L was >90% only for continuous infusion regimens of 400 mg/kg/day vs. 9.7% for the current DPF dose (80 mg/kg/6 h, 30 min infusion). Amikacin PTA was >90% with 20 mg/kg/d, higher than the PTA of the DPF dose of 15 mg/kg/d (63.5%). Using our new decision framework, altered DPF doses were proposed for piperacillin (better PTA with loading dose plus continuous infusion), but not for amikacin (studied and target population were not comparable and risk for toxicity with higher dose).

Conclusions: We show the feasibility to develop model-informed dosing guidelines for clinical implementation using existing pharmacokinetic data. This approach could complement literature and consensus-based dosing guidelines for off-label drugs in the absence of stronger evidence to support pediatricians in daily practice.

Estimation of piperacillin clearance with different glomerular filtration rate formulas in critically ill children

AIMS

Glomerular filtration rate (GFR) is difficult to assess in critically ill children using gold standard method and alternatives are needed. This study aimed to determine the most accurate GFR estimation formula for assessing piperacillin clearance in critically ill children, using a published piperacillin pharmacokinetics (PK) population model.

METHODS

All children hospitalized in the paediatric intensive care unit of a single institution who were receiving piperacillin were included. PK were described using the nonlinear mixed effect modelling software MONOLIX. In the initial PK model, GFR was estimated according to the Schwartz 1976 formula. We evaluated a set of 12 additional validated formulas, developed using plasma creatinine and/or cystatin C concentrations, in the building model to assess the lowest between-subject variability for piperacillin clearance.

RESULTS

We included 20 children with a median (range) postnatal age of 1.9 (0.1-19) years, body weight of 12.5 (3.5-69) kg. Estimated GFR according to the Schwartz 1976 formula was 160.5 (38-315) mL min^-1 1.73 m^-2 . Piperacillin clearance was best predicted by the Bouvet combined formula.

CONCLUSION

The combined Bouvet formula was the most accurate GFR estimation formula for assessing piperacillin clearance in critically ill children.

Augmented Renal Clearance and How to Augment Antibiotic Dosing

Augmented renal clearance (ARC) refers to the state of heightened renal filtration commonly observed in the critically ill. Its prevalence in this patient population is a consequence of the body’s natural response to serious disease, as well as the administration of fluids and pharmacologic therapies necessary to maintain sufficient blood pressure. ARC is objectively defined as a creatinine clearance of more than 130 mL/min/1.73 m² and is thus a crucial condition to consider when administering antibiotics, many of which are cleared renally. Using conventional dosing regimens risks the possibility of subtherapeutic concentrations or clinical failure. Over the past decade, research has been conducted in patients with ARC who received a number of antibacterials frequently used in the critically ill, such as piperacillin-tazobactam or vancomycin. Strategies to contend with this condition have also been explored, though further investigations remain necessary.

Augmented renal clearance in pediatric intensive care: are we undertreating our sickest patients?

Many critically ill patients display a supraphysiological renal function with enhanced renal perfusion and glomerular hyperfiltration. This phenomenon described as augmented renal clearance (ARC) may result in enhanced drug elimination through renal excretion mechanisms. Augmented renal clearance seems to be triggered by systemic inflammation and therapeutic interventions in intensive care. There is growing evidence that ARC is not restricted to the adult intensive care population, but is also prevalent in critically ill children. Augmented renal clearance is often overlooked due to the lack of reliable methods to assess renal function in critically ill children. Standard equations to calculate glomerular filtration rate (GFR) are developed for patients who have a steady-state creatinine production and a stable renal function. Those formulas are not reliable in critically ill patients with acutely changing GFR and tend to underestimate true GFR in patients with ARC. Tools for real-time, continuous, and non-invasive measurement of fluctuating GFR are most needed to identify changes in kidney function during critical illness and therapeutic interventions. Such devices are currently being validated and hold a strong potential to become the standard of practice. In the meantime, urinary creatinine clearance is considered the most reliable method to detect ARC in critically ill patients. Augmented renal clearance is clearly associated with subtherapeutic antimicrobial concentrations and subsequent therapeutic failure. This warrants the need for adjusted dosing regimens to optimize pharmacokinetic and pharmacodynamic target attainment. This review aims to summarize current knowledge on ARC in critically ill children, to give insight into its possible pathophysiological mechanism, to evaluate screening methods for ARC in the pediatric intensive care population, and to illustrate the effect of ARC on drug exposure, therapeutic efficacy, and clinical outcome.

Use of Simulation Strategies to Predict Subtherapeutic Meropenem Exposure Caused by Augmented Renal Clearance in Critically Ill Pediatric Patients With Sepsis

OBJECTIVES

The objectives of this study were to 1) define extent and potential clinical impact of increased or decreased renal elimination of meropenem in children with sepsis, based on analysis of renal function during the first 2 days of PICU stay; and 2) estimate the risk of subtherapeutic meropenem exposure attributable to increased renal clearance.

METHODS

This retrospective study evaluated patients with a diagnosis of sepsis, receiving meropenem from the PICU at Rady Children's Hospital San Diego from 2015-2017. Meropenem exposure was estimated by using FDA-approved doses (20 and 40 mg/kg/dose) on day 1 and day 2 of PICU stay, based on a population pharmacokinetic (PK) model. For this population with sepsis, we assessed time-above-minimum inhibitory concentration (T>MIC) for pathogen MICs.

RESULTS

Meropenem treatment was documented in 105 episodes of sepsis with a 48% rate of pathogen detection. By day 2, increased eGFR (>120 mL/min/1.73 m2) was documented in 49% of patients, with 17% meeting criteria for augmented renal clearance ([ARC] >160 mL/min/1.73 m2) and 10%, for decreased function. Simulations documented that 80% of PICU patients with ARC did not achieve therapeutic meropenem exposure for Pseudomonas aeruginosa with a MIC of 2, using standard doses to achieve a pharmacodynamic goal of 80% T>MIC.

CONCLUSIONS

Approximately 3 of every 20 children with sepsis exhibited ARC during the first 48 hours of PICU stay. Simulations documented an increased risk for subtherapeutic meropenem exposure, suggesting that higher meropenem doses may be required to achieve adequate antibiotic exposure early in the PICU course.

Population Pharmacokinetics and Safety of Piperacillin-Tazobactam Extended Infusions in Infants and Children

Piperacillin-tazobactam (TZP) is frequently used to treat severe hospital-acquired infections in children. We performed a single-center, pharmacokinetic (PK) trial of TZP in children ranging in age from 2 months to 6 years from various clinical subpopulations. Children who were on TZP per the standard of care were prospectively included and assigned to receive a dose of 80 mg/kg of body weight every 6 h infused over 2 h (ages 2 to 5 months) or a dose of 90 mg/kg every 8 h infused over 4 h (ages 6 months to 6 years). Separate population PK models were developed for piperacillin and tazobactam using nonlinear mixed-effects modeling. Optimal dosing was judged based on the ability to maintain free piperacillin concentrations above the piperacillin MIC for enterobacteria and Pseudomonas aeruginosa for ≥50% of the dosing interval. Any untoward event occurring during treatment was collected as an adverse event. A total of 79 children contributed 174 PK samples. The median (range) age and weight were 1.7 years (2 months to 6 years) and 11.4 kg (3.8 to 27.6 kg), respectively. A 2-compartment model with first-order elimination best described the piperacillin and tazobactam data. Both final population PK models included weight and concomitant furosemide administration on clearance and weight on the volume of distribution of the central compartment. The optimal dosing regimens in children with normal renal function, based on the piperacillin component, were 75 mg/kg/dose every 4 h infused over 0.5 h in infants ages 2 to ≤6 months and 130 mg/kg/dose every 8 h infused over 4 h in children ages >6 months to 6 years against bacteria with MICs up to 16 mg/liter. A total of 44 children (49%) had ≥1 adverse event, with 3 of these (site infiltrations) considered definitely associated with the extended infusions.

Population pharmacokinetics of piperacillin in febrile children receiving cancer chemotherapy: the impact of body weight and target on an optimal dosing regimen

BACKGROUND

The β-lactam antibiotic piperacillin (in combination with tazobactam) is commonly chosen for empirical treatment of suspected bacterial infections. However, pharmacokinetic variability among patient populations and across ages leads to uncertainty when selecting a dosing regimen to achieve an appropriate pharmacodynamic target.

OBJECTIVES

To guide dosing by establishing a population pharmacokinetic model for unbound piperacillin in febrile children receiving cancer chemotherapy, and to assess pharmacokinetic/pharmacodynamic target attainment (100% fT > 1×MIC and 50% fT > 4×MIC) and resultant exposure, across body weights.

METHODS

Forty-three children admitted for 89 febrile episodes contributed 482 samples to the pharmacokinetic analysis. The typical doses required for target attainment were compared for various dosing regimens, in particular prolonged infusions, across MICs and body weights.

RESULTS

A two-compartment model with inter-fever-episode variability in CL, and body weight included through allometry, described the data. A high CL of 15.4 L/h (70 kg) combined with high glomerular filtration rate (GFR) values indicated rapid elimination and hyperfiltration. The target of 50% fT > 4×MIC was achieved for an MIC of 4.0 mg/L in a typical patient with extended infusions of 2-3 (q6h) or 3-4 (q8h) h, at or below the standard adult dose (75 and 100 mg/kg/dose for q6h and q8h, respectively). Higher doses or continuous infusion were needed to achieve 100% fT > 1×MIC due to the rapid piperacillin elimination.

CONCLUSIONS

The licensed dose for children with febrile neutropenia (80 mg/kg q6h as a 30 min infusion) performs poorly for attainment of fT>MIC pharmacokinetic/pharmacodynamic targets. Given the population pharmacokinetic profile, feasible dosing regimens with reasonable exposure are continuous infusion (100% fT > 1×MIC) or prolonged infusions (50% fT > 4×MIC).

Application of Size and Maturation Functions to Population Pharmacokinetic Modeling of Pediatric Patients

Traditionally, dosage for pediatric patients has been optimized using simple weight-scaled methods, but these methods do not always meet the requirements of children. To overcome this discrepancy, population pharmacokinetic (PK) modeling of size and maturation functions has been proposed. The main objective of the present study was to evaluate a new modeling method for pediatric patients using clinical data from three different clinical studies. To develop the PK models, a nonlinear mixed effect modeling method was employed, and to explore PK differences in pediatric patients, size with allometric and maturation with Michaelis–Menten type functions were evaluated. Goodness of fit plots, visual predictive check and bootstrap were used for model evaluation. Single application of size scaling to PK parameters was statistically significant for the over one year old group. On the other hand, simultaneous use of size and maturation functions was statistically significant for infants younger than one year old. In conclusion, population PK modeling for pediatric patients was successfully performed using clinical data. Size and maturation functions were applied according to established criteria, and single use of size function was applicable for over one year ages, while size and maturation functions were more effective for PK analysis of neonates and infants.