Amikacin population pharmacokinetics among paediatric burn patients

Exploring the Past to Inform the Future to Optimize the Pharmacokinetics of Vancomycin in Children With Severe Burn Injuries

Sepsis remains one of the leading causes of death among pediatric patients with burn injuries. Despite limited vancomycin pharmacokinetic (PK) information within this population, it is widely used to treat severe burn injuries. Those with severe burns are at risk of nephrotoxicity, with an incidence of acute kidney injury (AKI) over 50%. Delivering an effective vancomycin dose and avoiding unnecessary toxicity is essential for improved patient outcomes. This was a retrospective analysis of 115 children aged 0.2 months to 18 years with severe burns, >10% total body surface area. Vancomycin was given via intravenous infusion; blood samples were drawn between 6- and 12-hour postinfusion. A population pharmacokinetic model was developed using nonlinear mixed-effect modeling (Monolix, version 2016R1). A one-compartment model described a steady-state volume of distribution (V), dependent on weight. Vancomycin clearance (CL) was influenced by age and estimated creatinine clearance (CrCL). The study population's (median age = 4 years, median weight = 20 kg, median total body surface area (%TBSA) = 40%) median V and CL were calculated to be 1.25 L/kg (95% CI, 1.04-1.46) and 0.15 L/h/kg (95% CI, 0.126-0.165), respectively. The PK model was explicitly developed to characterize the impact of physiological changes in children under 18 years of age and the percentage of the burn surface area using limited data. The analysis determined that weight, age, and estimated CrCL were important covariates in predicting vancomycin PK with high variability in CL and V.

Amikacin Therapy in Japanese Pediatric Patients: Narrative Review

Children show a very wide range of physical development processes. These changes impact pharmacokinetic (PK) variability in pediatric patients. Most PK studies have been conducted on the Caucasian population. Therefore, whether current evidence of how developmental change affects PK and exposure-response relationships applies to Japanese pediatric patients remains unclear. This narrative review focuses on amikacin therapy in Japanese pediatric patients and shows the relationship between amikacin concentrations and efficacy/toxicity. Ten relevant articles were identified. Of these, nine articles were published in the 1980s. All studies reported a maximum concentration (Cmax) and minimum concentration (Cmin) of amikacin. Overall, articles reporting PK/pharmacodynamic (PD) indices and minimum inhibitory concentration (MIC) of isolated bacteria in Japanese pediatric patients is lacking, whereas all patients recovered from an infection state and showed negative cultures. Five of the included studies reported the association between Cmin and toxicity. The Cmin in three of four patients who developed toxicity was above 10 mg/L. This narrative review shows that further PK study of amikacin in Japanese pediatric patients is necessary. In particular, the pursuit of knowledge of Cmax/MIC ratio is vital. On the other hand, this review demonstrates that the optimal Cmin for Japanese pediatric patients is below 10 mg/L as a candidate concentration. However, it is noted that the number of patients who developed toxicity is very small.

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.

Amikacin initial dosage in patients with hypoalbuminaemia: an interactive tool based on a population pharmacokinetic approach

OBJECTIVES

To characterize amikacin population pharmacokinetics in patients with hypoalbuminaemia and to develop a model-based interactive application for amikacin initial dosage.

METHODS

A population pharmacokinetic model was developed using a non-linear mixed-effects modelling approach (NONMEM) with amikacin concentration-time data collected from clinical practice (75% hypoalbuminaemic patients). Goodness-of-fit plots, minimum objective function value, prediction-corrected visual predictive check, bootstrapping, precision and bias of parameter estimates were used for model evaluation. An interactive model-based simulation tool was developed in R (Shiny and R Markdown). Cmax/MIC ratio, time above MIC and AUC/MIC were used for optimizing amikacin initial dose recommendation. Probabilities of reaching targets were calculated for the dosage proposed.

RESULTS

A one-compartment model with first-order linear elimination best described the 873 amikacin plasma concentrations available from 294 subjects (model development and external validation groups). Estimated amikacin population pharmacokinetic parameters were CL (L/h) = 0.525 + 4.78 × (CKD-EPI/98) × (0.77 × vancomycin) and V (L) = 26.3 × (albumin/2.9)-0.51 × [1 + 0.006 × (weight - 70)], where CKD-EPI is calculated with the Chronic Kidney Disease Epidemiology Collaboration equation. AMKdose is a useful interactive model-based application for a priori optimization of amikacin dosage, using individual patient and microbiological information together with predefined pharmacokinetic/pharmacodynamic (PKPD) targets.

CONCLUSIONS

Serum albumin, total bodyweight, estimated glomerular filtration rate (using the CKD-EPI equation) and co-medication with vancomycin showed a significant impact on amikacin pharmacokinetics. A powerful interactive initial dose-finding tool has been developed and is freely available online. AMKdose could be useful for guiding initial amikacin dose selection before any individual pharmacokinetic information is available.

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.

Evaluation of Current Amikacin Dosing Recommendations and Development of an Interactive Nomogram: The Role of Albumin

This study aimed to evaluate the potential efficacy and safety of the amikacin dosage proposed by the main guidelines and to develop an interactive nomogram, especially focused on the potential impact of albumin on initial dosage recommendation. The probability of target attainment (PTA) for each of the different dosing recommendations was calculated through stochastic simulations based on pharmacokinetic/pharmacodynamic (PKPD) criteria. Large efficacy and safety differences were observed for the evaluated amikacin dosing guidelines together with a significant impact of albumin concentrations on efficacy and safety. For all recommended dosages evaluated, efficacy and safety criteria of amikacin dosage proposed were not achieved simultaneously in most of the clinical scenarios evaluated. Furthermore, a significant impact of albumin was identified: The higher is the albumin, (i) the higher will be the PTA for maximum concentration/minimum inhibitory concentration (Cmax/MIC), (ii) the lower will be the PTA for the time period with drug concentration exceeding MIC (T_>MIC) and (iii) the lower will be the PTA for toxicity (minimum concentration). Thus, accounting for albumin effect might be of interest for future amikacin dosing guidelines updates. In addition, AMKnom, an amikacin nomogram builder based on PKPD criteria, has been developed and is freely available to help evaluating dosing recommendations.

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.

A Status Update on Pharmaceutical Analytical Methods of Aminoglycoside Antibiotic: Amikacin

Amikacin (AMK) is one of the commonly used aminoglycoside antibiotics, introduced for clinical use in patients suffering from bacterial infections especially life-threatening gram-negative infections. Due to lack of chromophore in the molecule, the detection of AMK during analysis is a challenge. Thus, pre and post-column derivatization techniques are generally used for AMK estimation. This review focuses on different analytical methods used for detection and quantification of AMK in pure or fixed dose combination pharmaceutical formulations and biological samples. Various reported methods described in the literature include high-performance liquid chromatography techniques, pulsed electrochemical detection techniques, Chemiluminescence techniques, Capillary electrophoresis and immunological methods. High-performance-liquid-chromatography based methods with UV/Vis spectrophotometric, fluorescence and mass spectrometric detection are the most prevailing methods employed for the analysis of AMK. This review could be of significant importance in the area of future AMK analytical method development studies.

A Retrospective Evaluation of Allometry, Population Pharmacokinetics, and Physiologically-Based Pharmacokinetics for Pediatric Dosing Using Clearance as a Surrogate

Physiologically-based pharmacokinetic models are increasingly applied for pediatric dose selection along with traditional methods such as allometry and population pharmacokinetic models. We report a retrospective evaluation of the three methods. Pediatric population pharmacokinetic models sourced from literature for a subset of eight compounds were used to predict clearances for children < 2 years when they were within the modeled age range (interpolation, N = 11) or including those outside the modeled age range (interpolation and extrapolation, N = 18). Pediatric/adult clearance ratios were evaluated with a strict performance criterion of 0.8-1.25 and with twofold criteria. For children > 2 years, 58-75% of the clinical studies (N = 10) met the strict criteria, and > 80% of the clinical studies were predicted within twofold by all three methods. For children < 2 years, physiologically-based pharmacokinetic, allometry with age-dependent exponents, and pediatric population pharmacokinetic models predict 54%, 82%, and 64% within twofold of the observed, respectively.

Population Pharmacokinetics of Amikacin in Adult Patients with Cystic Fibrosis

Practitioners commonly use amikacin in patients with cystic fibrosis. Establishment of the pharmacokinetics of amikacin in adults with cystic fibrosis may increase the efficacy and safety of therapy. This study was aimed to establish the population pharmacokinetics of amikacin in adults with cystic fibrosis. We used serum concentration data obtained during routine therapeutic drug monitoring and explored the influence of patient covariates on drug disposition. We performed a retrospective chart review to collect the amikacin dosing regimens, serum amikacin concentrations, blood sampling times, and patient characteristics for adults with cystic fibrosis admitted for treatment of acute pulmonary exacerbations. Amikacin concentrations were retrospectively collected for 49 adults with cystic fibrosis, and 192 serum concentrations were available for analysis. A population pharmacokinetic model was developed using nonlinear mixed-effects modeling with the first-order conditional estimation method. A two-compartment model with first-order elimination best described amikacin pharmacokinetics. Creatinine clearance and weight were identified as significant covariates for clearance and the volume of distribution, respectively, in the final model. Residual variability was modeled using a proportional error model. Typical estimates for clearance, central and peripheral volumes of distribution, and intercompartmental clearance were 3.06 liters/h, 14.4 liters, 17.1 liters, and 0.925 liters/h, respectively. The pharmacokinetics of amikacin in individuals with cystic fibrosis seems to differ from those in individuals without cystic fibrosis. However, further investigations are needed to confirm these results and, thus, the need for variations in amikacin dosing. Future pharmacodynamic studies will potentially establish the optimal amikacin dosing regimens for the treatment of acute pulmonary exacerbations in adult patients with CF.

Optimizing Amikacin Dosage in Pediatrics Based on Population Pharmacokinetic/Pharmacodynamic Modeling

OBJECTIVE

Our objective was to determine the population pharmacokinetic parameters of amikacin in pediatric patients to contribute to the future development of a revised optimum dose and population-specific dosing regimens.

METHODS

We performed a retrospective chart review in non-critical pediatric patients (aged 1-12 years) who received amikacin for suspected or proven Gram-negative infection at a university hospital. The population pharmacokinetic models were developed using Monolix 4.4. Pharmacokinetic/pharmacodynamic (PK/PD) simulations were performed to explore the ability of different dosage regimens to achieve the pharmacodynamic targets.

RESULTS

The analysis included 134 amikacin plasma concentrations from 67 patients with a mean ± standard deviation age of 4.1 ± 3.9 years and bodyweight of 15 ± 8.4 kg. The patients received an amikacin total daily dose (TDD) of 23 ± 7.3 mg/kg, which resulted in peak and trough concentrations of 20.65 ± 7.6 and 2.4 ± 1.7 mg/l, respectively. The estimated pharmacokinetic parameters for amikacin were 1.2 l/h and 6.5 l for total body clearance (CL) and the volume of distribution (V), respectively. Dosing simulations showed that the standard dosing regimen (15 mg/kg/day) of amikacin achieved the PK/PD target of peak serum concentration (C_peak)/minimum inhibitory concentration (MIC) ≥ 8 for an MIC of 2 mg/l; higher doses were required to achieve higher MIC values.

CONCLUSION

The simulation results indicated that amikacin 20 mg/kg once daily provided a higher probability of target attainment with lower toxicity than dosing three times daily. In addition, combination therapy is recommended for pathogens with an MIC of ≥ 8 mg/l.

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.

Uncertainty in Antibiotic Dosing in Critically Ill Neonate and Pediatric Patients: Can Microsampling Provide the Answers?

PURPOSE

With a decreasing supply of antibiotics that are effective against the pathogens that cause sepsis, it is critical that we learn to use currently available antibiotics optimally. Pharmacokinetic studies provide an evidence base from which we can optimize antibiotic dosing. However, these studies are challenging in critically ill neonate and pediatric patients due to the small blood volumes and associated risks and burden to the patient from taking blood. We investigate whether microsampling, that is, obtaining a biologic sample of low volume (<50 μL), can improve opportunities to conduct pharmacokinetic studies.

METHODS

We performed a literature search to find relevant articles using the following search terms: sepsis, critically ill, severe infection, intensive care AND antibiotic, pharmacokinetic, p(a)ediatric, neonate. For microsampling, we performed a search using antibiotics AND dried blood spots OR dried plasma spots OR volumetric absorptive microsampling OR solid-phase microextraction OR capillary microsampling OR microsampling. Databases searched include Web of Knowledge, PubMed, and EMbase.

FINDINGS

Of the 32 antibiotic pharmacokinetic studies performed on critically ill neonate or pediatric patients in this review, most of the authors identified changes to the pharmacokinetic properties in their patient group and recommended either further investigations into this patient population or therapeutic drug monitoring to ensure antibiotic doses are suitable. There remain considerable gaps in knowledge regarding the pharmacokinetic properties of antibiotics in critically ill pediatric patients. Implementing microsampling in an antibiotic pharmacokinetic study is contingent on the properties of the antibiotic, the pathophysiology of the patient (and how this can affect the microsample), and the location of the patient. A validation of the sampling technique is required before implementation.

IMPLICATIONS

Current antibiotic regimens for critically ill neonate and pediatric patients are frequently suboptimal due to a poor understanding of altered pharmacokinetic properties. An assessment of the suitability of microsampling for pharmacokinetic studies in neonate and pediatric patients is recommended before wider use. The method of sampling, as well as the method of bioanalysis, also requires validation to ensure the data obtained reflect the true result.

Gap analysis of pharmacokinetics and pharmacodynamics in burn patients: a review

Severe burn injury results in a multifaceted physiological response that significantly alters drug pharmacokinetics and pharmacodynamics (PK/PD). This response includes hypovolemia, increased vascular permeability, increased interstitial hydrostatic pressure, vasodilation, and hypermetabolism. These physiologic alterations impact drug distribution and excretion-thus varying the drug therapeutic effect on the body or microorganism. To this end, in order to optimize critical care for the burn population it is essential to understand how burn injury alters PK/PD parameters. The purpose of this article is to describe the relationship between burn injury and drug PK/PD. We conducted a literature review via PubMed and Google to identify burn-related PK/PD studies. Search parameters included "pharmacokinetics," "pharmacodynamics," and "burns." Based on our search parameters, we located 38 articles that studied PK/PD parameters specifically in burns. Twenty-seven articles investigated PK/PD of antibiotics, 10 assessed analgesics and sedatives, and one article researched an antacid. Out of the 37 articles, there were 19 different software programs used and eight different control groups. The mechanisms behind alterations in PK/PD in burns remain poorly understood. Dosing techniques must be adapted based on burn injury-related changes in PK/PD parameters in order to ensure drug efficacy. Although several PK/PD studies have been undertaken in the burn population, there is wide variation in the analytical techniques, software, and study sample sizes used. In order to refine dosing techniques in burns and consequently improve patient outcomes, there must be harmonization among PK/PD analyses.

Effect of Kidney Function on Drug Kinetics and Dosing in Neonates, Infants, and Children

Neonates, infants, and children differ from adults in many aspects, not just in age, weight, and body composition. Growth, maturation and environmental factors affect drug kinetics, response and dosing in pediatric patients. Almost 80% of drugs have not been studied in children, and dosing of these drugs is derived from adult doses by adjusting for body weight/size. As developmental and maturational changes are complex processes, such simplified methods may result in subtherapeutic effects or adverse events. Kidney function is impaired during the first 2 years of life as a result of normal growth and development. Reduced kidney function during childhood has an impact not only on renal clearance but also on absorption, distribution, metabolism and nonrenal clearance of drugs. 'Omics'-based technologies, such as proteomics and metabolomics, can be leveraged to uncover novel markers for kidney function during normal development, acute kidney injury, and chronic diseases. Pharmacometric modeling and simulation can be applied to simplify the design of pediatric investigations, characterize the effects of kidney function on drug exposure and response, and fine-tune dosing in pediatric patients, especially in those with impaired kidney function. One case study of amikacin dosing in neonates with reduced kidney function is presented. Collaborative efforts between clinicians and scientists in academia, industry, and regulatory agencies are required to evaluate new renal biomarkers, collect and share prospective pharmacokinetic, genetic and clinical data, build integrated pharmacometric models for key drugs, optimize and standardize dosing strategies, develop bedside decision tools, and enhance labels of drugs utilized in neonates, infants, and children.