Pharmacokinetics of Antimicrobials in Obese Children

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

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

Risk Factors Associated with Suboptimal Tobramycin Levels in the Medical Intensive Care Unit

BACKGROUND

Optimal aminoglycoside dosing in critically ill patients represents a challenge for practitioners, especially in the medical intensive care unit (MICU). MICU patients exhibit altered pharmacokinetics due to pathophysiological changes the body undergoes in critical illness, leading to possible treatment failure. The literature surrounding optimal dosing and therapeutic drug monitoring strategies of aminoglycosides in MICU patients is scarce and conflicting. Additionally, only a few studies have investigated risk factors for suboptimal pharmacokinetic target obtainment. Currently, no definitive risk factors have been identified to predict suboptimal aminoglycoside target obtainment in MICU patients.

OBJECTIVE

The objective of this study was to determine risk factors for suboptimal pharmacokinetic target obtainment in patients receiving tobramycin in the MICU.

METHODS

This single-center, retrospective cohort study included patients 18-89 years old who received at least one 7 mg/kg tobramycin dose in the MICU from January, 1 2015 to September, 30 2020. Patients also had to have at least two detectable drug levels obtained at least one half-life apart following the first tobramycin dose. The primary outcome was to determine the incidence of optimal pharmacokinetic target obtainment, defined as a tobramycin maximum concentration (C_max) ≥ 10 mcg/ml, and to identify the risk factors for suboptimal (C_max < 10 mcg/mL) pharmacokinetic target obtainment, in MICU patients. Secondary outcomes were compared between suboptimal and optimal target obtainment in patients with culture confirmed gram-negative infection susceptible to tobramycin. These secondary outcomes included all-cause in-hospital mortality, ICU length of stay (LOS), hospital LOS, and vasopressor duration in those with shock.

RESULTS

A total of 230 patients were included in this retrospective study. For the primary outcome, 187 (81.3%) patients achieved optimal target obtainment. Through multivariate logistic regression, female sex and serum albumin < 2.5 g/dL were identified as independent risk factors for suboptimal target obtainment; [OR = 2.14; 95% CI (1.05-4.37), p = 0.037], [OR = 2.50; 95% CI (1.21-5.19), p = 0.014], respectively. Fifty-four (23%) patients had culture-confirmed gram-negative infections susceptible to tobramycin and were included in the subgroup analysis. Of these 54 patients, 11 (20.4%) did not achieve optimal target concentrations. In patients with culture-confirmed gram-negative infection, there was no difference between patients with optimal target obtainment and suboptimal target obtainment in ICU LOS, hospital LOS, all-cause mortality, or vasopressor duration in those with shock.

CONCLUSIONS

Among patients receiving their first dose of tobramycin in the MICU, 81.3% obtained an optimal serum concentration. Female sex and serum albumin < 2.5 g/dL were identified as risk factors for suboptimal target obtainment; however, further research is warranted to assess the utility of using these two covariates as risk factors for more aggressive dosing in critically ill MICU patients.

Pediatric obesity and perioperative medicine

PURPOSE OF REVIEW

Childhood obesity is a public health emergency that has reached a pandemic level and imposed a massive economic burden on healthcare systems. Our objective was to provide an update on (1) challenges of obesity definition and classification in the perioperative setting, (2) challenges of perioperative patient positioning and vascular access, (3) perioperative implications of childhood obesity, (3) anesthetic medication dosing and opioid-sparing techniques in obese children, and (4) research gaps in perioperative childhood obesity research including a call to action.

RECENT FINDINGS

Despite the near axiomatic observation that obesity is a pervasive clinical problem with considerable impact on perioperative health, there have only been a handful of research into the many ramifications of childhood obesity in the perioperative setting. A nuanced understanding of the surgical and anesthetic risks associated with obesity is essential to inform patients' perioperative consultation and their parents' counseling, improve preoperative risk mitigation, and improve patients' rescue process when complications occur.

SUMMARY

Anesthesiologists and surgeons will continue to be confronted with an unprecedented number of obese or overweight children with a high risk of perioperative complications.

Estimation of Body Fat Percentage for Clinical Pharmacokinetic Studies in Children

Obesity is a prevalent childhood condition and the degree of adiposity appears likely to be an important covariate in the pharmacokinetics (PKs) of many drugs. We undertook these studies to facilitate the evaluation and, where appropriate, quantification of the covariate effect of body fat percentage (BF%) on PK parameters in children. We examined two large databases to determine the values and variabilities of BF% in children with healthy body weights and in those with obesity, comparing the accuracy and precision of BF% estimation by both clinical methods and demographically derived techniques. Additionally, we conducted simulation studies to evaluate the utility of the several methods for application in clinical trials. BF% was correlated with body mass index (BMI), but was highly variable among both children with healthy body weights and those with obesity. Bio-impedance and several demographically derived techniques produced mean estimates of BF% that differed from dual x-ray absorptiometry by < 1% (accuracy) and a SD of 5% or less (precision). Simulation studies confirmed that when the differences in precision among the several methods were small compared with unexplained between-subject variability of a PK parameter, the techniques were of similar value in assessing the contribution of BF%, if any, as a covariate for that PK parameter. The combination of sex and obesity stage explained 68% of the variance of BF% with BMI. The estimation of BF% from sex and obesity stage can routinely be applied to PK clinical trials to evaluate the contribution of BF% as a potential covariate.

A Population-Based Pharmacokinetic Model Approach to Pantoprazole Dosing for Obese Children and Adolescents

BACKGROUND AND AIMS

Pharmacokinetic data for proton pump inhibitors (PPIs), acid-suppression drugs commonly prescribed to children, are lacking for obese children who are at greatest risk for acid-related disease. In a recent multi-center investigation, we demonstrated decreased, total body weight adjusted, apparent clearance (CL/F) of the PPI pantoprazole for obese children compared with their non-obese peers. Subsequently, we developed a population-based pharmacokinetic (PopPK) model to characterize pantoprazole disposition and evaluated appropriate pantoprazole dosing strategies for obese pediatric patients, using simulation.

METHODS

Pharmacokinetic data from the only prospective study of PPIs in obese children (aged 6-17 years; n = 40) included 273 pantoprazole and 256 pantoprazole-sulfone plasma concentrations, after single oral-dose administration, and were used for pantoprazole model development and covariate analysis (NONMEM®). Model evaluation was performed via bootstrapping and predictive checks, and the final model was applied to simulate systemic pantoprazole exposures for common dosing scenarios.

RESULTS

A two-compartment PopPK model, which included CYP2C19 genotype and total body weight, provided the best fit. Resultant, typical, weight-normalized pantoprazole parameter estimates were different than previously reported for children or adults, with significantly reduced pantoprazole CL/F for obese children. Of the dosing scenarios evaluated, the weight-tiered approach, approved by the US Food and Drug Administration, achieved pantoprazole exposures [area under the curve (AUC0-∞)] within ranges previously reported as therapeutic, without over- or under-prediction for obese children.

CONCLUSIONS

Our data argue against empiric dose escalation of PPIs for obese children and support current FDA-approved pediatric weight-tiered dosing for pantoprazole; however, 3- to 5-fold inter-individual variability in pantoprazole AUC0-∞ remained using this dosing approach.

Taking a bite out of nutrition and arbovirus infection

Nutrition is a key factor in host–pathogen defense. Malnutrition can increase both host susceptibility and severity of infection through a number of pathways, and infection itself can promote nutritional deterioration and further susceptibility. Nutritional status can also strongly influence response to vaccination or therapeutic pharmaceuticals. Arthropod-borne viruses (arboviruses) have a long history of infecting humans, resulting in regular pandemics as well as an increasing frequency of autochthonous transmission. Interestingly, aside from host-related factors, nutrition could also play a role in the competence of vectors required for transmission of these viruses. Nutritional status of the host and vector could even influence viral evolution itself. Therefore, it is vital to understand the role of nutrition in the arbovirus lifecycle. This Review will focus on nutritional factors that could influence susceptibility and severity of infection in the host, response to prophylactic and therapeutic strategies, vector competence, and viral evolution.

As the old adage goes, you are what you eat. Proper nutrition is a cornerstone of health, and malnutrition can seriously impair the function of the immune system, resulting in increased infections or a more severe disease. Imbalanced or inadequate nutrition can also affect responses to vaccines or drugs that are vital for protection and treatment against viruses. A mosquito is also a product of what it eats. Nutrition during development and adult lifecycle can affect the feeding behavior of mosquitoes, thereby affecting transmission of viral diseases. Arthropod-borne viruses (arboviruses) are a major global health concern, especially in areas impacted by malnutrition. Understanding how nutrition can affect both humans and mosquitoes in the context of these viruses is vital to combating these diseases.

Drug Dosing in Obese Children: Challenges and Evidence-Based Strategies

With the alarming increase of obesity in children, pediatricians are increasingly being confronted with difficult dosing decisions. Many drug labels do not provide specific dosing instructions for children who are obese. In this article, we describe the physiologic parameters altered by obesity and their influences on drug disposition and effect. We review the principles of allometry, and the key pharmacokinetic parameters that can be used to derive age appropriate dosing regimens. Last, we illustrate how appropriate weight descriptors can be selected, and how important PK parameters can be extrapolated for dosing in obese children when pediatric pharmacokinetic information is available.

Pediatric Obesity: Pharmacokinetic Alterations and Effects on Antimicrobial Dosing

Limited data exist for appropriate drug dosing in obese children. This comprehensive review summarizes pharmacokinetic (PK) alterations that occur with age and obesity, and these effects on antimicrobial dosing. A thorough comparison of different measures of body weight and specific antimicrobial agents including cefazolin, cefepime, ceftazidime, daptomycin, doripenem, gentamicin, linezolid, meropenem, piperacillin-tazobactam, tobramycin, vancomycin, and voriconazole is presented. PubMed (1966-July 2015) and Cochrane Library searches were performed using these key terms: children, pharmacokinetic, obesity, overweight, body mass index, ideal body weight, lean body weight, body composition, and specific antimicrobial drugs. PK studies in obese children and, if necessary, data from adult studies were summarized. Knowledge of PK alterations stemming from physiologic changes that occur with age from the neonate to adolescent, as well as those that result from increased body fat, become an essential first step toward optimizing drug dosing in obese children. Excessive amounts of adipose tissue contribute significantly to body size, total body water content, and organ size and function that may modify drug distribution and clearance. PK studies that evaluated antimicrobial dosing primarily used total (or actual) body weight (TBW) for loading doses and TBW or adjusted body weight for maintenance doses, depending on the drugs' properties and dosing units. PK studies in obese children are imperative to elucidate drug distribution, clearance, and, consequently, the dose required for effective therapy in these children. Future studies should evaluate the effects of both age and obesity on drug dosing because the incidence of obesity is increasing in pediatric patients.

Cefazolin Irreversibly Inhibits Proliferation and Migration of Human Mesenchymal Stromal Cells

Drugs may have a significant effect on postoperative bone healing by reducing the function of human mesenchymal stromal cells (hMSC) or mature osteoblasts. Although cefazolin is one of the most commonly used antibiotic drugs in arthroplasty to prevent infection worldwide, there is a lack of information regarding how cefazolin affects hMSC and therefore may have an effect on early bone healing. We studied the proliferation and migration capacity of primary hMSC during cefazolin treatment at various doses for up to 3 days, as well as the reversibility of the effects during the subsequent 3 days of culture without the drug. We found a time- and dose-dependent reduction of the proliferation rate and the migratory potential. Tests of whether these effects were reversible revealed that doses ≥250 μg/mL or treatments longer than 24 h irreversibly affected the cells. We are the first to show that application of cefazolin irreversibly inhibits the potential of hMSC for migration to the trauma site and local proliferation. Cefazolin should be administered only at the required dosage and time to prevent periprosthetic infection. If long-term administration is required and delayed bone healing is present, cefazolin application must be considered as a cause of delayed bone healing.

Gaps in Drug Dosing for Obese Children: A Systematic Review of Commonly Prescribed Emergency Care Medications

PURPOSE

Approximately 1 of 6 children in the United States is obese. This has important implications for drug dosing and safety because pharmacokinetic (PK) changes are known to occur in obesity due to altered body composition and physiologic mechanisms. Inappropriate drug dosing in an emergency setting can limit therapeutic efficacy and increase drug-related toxic effects for obese children. Few systematic reviews examining PK properties and drug dosing in obese children have been performed.

METHODS

We identified 25 emergency care drugs from the Strategic National Stockpile and Acute Care Supportive Drugs List and performed a systematic review for each drug in 3 study populations: obese children (2-18 years of age), normal weight children, and obese adults (aged >18 years). For each study population, we first reviewed a drug's Food and Drug Administration label and then performed a systematic literature review. From the literature, we extracted drug PK data, biochemical properties, and dosing information. We then reviewed data in 3 age subpopulations (2-7 years, 8-12 years, and 13-18 years) for obese and normal weight children and by route of drug administration (intramuscular, intravenous, oral, and inhaled). If sufficient PK data were not available by age and route of administration, a data gap was identified.

FINDINGS

Only 2 of 25 emergency care drugs (8%) contained dosing information on the Food and Drug Administration label for obese children and adults compared with 22 of 25 (88%) for normal weight children. We found no sufficient PK data in the literature for any of the emergency care drugs in obese children. Sufficient PK data were found for 7 of 25 emergency care drugs (28%) in normal weight children and 3 of 25 (12%) in obese adults.

IMPLICATIONS

Insufficient information exists to guide dosing in obese children for any of the emergency care drugs reviewed. This knowledge gap is alarming, given the known PK changes that occur in the setting of obesity. Future clinical trials examining the PK properties of emergency care medications in obese children should be prioritized.