Population Pharmacokinetics of Intermittent Vancomycin in Children with Cystic Fibrosis

Population pharmacokinetics and target attainment analysis of vancomycin after intermittent dosing in adults with cystic fibrosis

Vancomycin is the first-line agent to treat pulmonary infections caused by methicillin-resistant Staphylococcus aureus (MRSA) in people with cystic fibrosis (PwCF). However, there is no consensus on vancomycin initial dosing in this population among health institutions, and there is a large variability in initial dosing across the United States. In this study, we characterized the pharmacokinetics (PK) of vancomycin in PwCF using a population PK approach. The clinical PK data to develop the population PK model were obtained from vancomycin therapeutic monitoring data from PwCF undergoing treatment for infections due to MRSA. The population PK model was then used to perform comprehensive Monte Carlo simulations to evaluate the probability of target attainment (PTA) of 12 different initial dosing scenarios. The area under the curve to minimum inhibitory concentration (MIC) ratio ≥400 mg*h/L and <650 mg*h/L were used as efficacy and toxicity targets for PTA analysis. A total of 181 vancomycin plasma concentrations were included in the analysis. A one-compartment model with first-order elimination best described the data. Weight significantly influenced the vancomycin PK (P < 0.05). In the final model, clearance was estimated as 5.52 L/h/70 kg, and the volume of distribution was 31.5 L/70 kg. The PTA analysis showed that at MIC = 1 µg/mL, doses 1,500 q8h and 2,000 q12h showed the highest %PTA in achieving both efficacy and toxicity targets. The PTA results from this study may potentially inform the initial dosing regimens of vancomycin to treat pulmonary infections due to MRSA in PwCF.

Implementation of a Pharmacist-Driven Vancomycin and Aminoglycoside Dosing Service in a Pediatric Hospital

OBJECTIVE

Pharmacy-driven antibiotic dosing services have been shown to improve clinical outcomes in adult patients. This study evaluated the effect of a pharmacist-driven antimicrobial dosing service on the percentage of therapeutic serum concentrations achieved following initial vancomycin or aminoglycoside dosing regimens. A secondary objective was to determine the effect of the dosing service on nephrotoxicity in pediatric patients.

METHODS

This single-center, retrospective study used data obtained from an electronic medical record to evaluate the utility of a pharmacist-driven vancomycin or aminoglycoside dosing protocol. Assessments of target, subtherapeutic, and supratherapeutic serum concentrations were evaluated. The occurrence of changes in serum creatinine and presentation of acute kidney injury (AKI) were also determined.

RESULTS

The incidence (n [%]) of a therapeutic initial serum concentration was not statistically significant between pre-protocol and post-protocol groups (21 [46.7%] vs 22 [48.9%], respectively; p = 0.834). The incidence of initial supratherapeutic concentrations (19 [42.2%] vs 7 [15.6%]; p = 0.005) and the average number of supratherapeutic concentrations per antibiotic course (0.76 vs 0.26; p = 0.01) were higher in the pre-protocol group compared with the post-protocol group. The incidence of AKI was significantly lower in the post-protocol group (2.2% vs 13.3%; p = 0.049).

CONCLUSIONS

Implementation of a pharmacist-driven dosing service did not affect the likelihood of achieving an initial therapeutic concentration. However, it did reduce the likelihood of both supratherapeutic concentrations and AKI. Additional studies in pediatric patients are needed to affirm the use of pharmacist dosing services.

Establishment and application of population pharmacokinetics model of vancomycin in infants with meningitis

BACKGROUND

To establish a population pharmacokinetics (PPK) model of vancomycin (VCM) for dose individualization in Chinese infants with meningitis.

METHODS

We collected the data of 82 children with meningitis in hospital from July 2014 to June 2016. The initial vancomycin dosage regimen for children was 10 or 15 mg/kg for q12 h, q8 h or q6 h. Serum concentrations were determined by Viva-E Analyzer before and after the fifth administration. The PPK model was developed by nonlinear mixed-effect model software, assessed by the bootstrap method and then tested in 20 infant patients.

RESULTS

The VCM clearance (CL) was increased by body weight (WT) and decreased by blood urea nitrogen (BUN). Pharmacokinetic parameters of VCM were not influenced by co-administered drugs. The trough concentrations of VCM were accurately predicted by the PPK model, with the prediction errors less than 32%.

CONCLUSION

A new individual strategy for VCM regimens was proposed and validated by the PPK model.

Dose Tailoring of Vancomycin Through Population Pharmacokinetic Modeling Among Surgical Patients in Pakistan

Background: Vancomycin is a narrow therapeutic agent, and it is necessary to optimize the dose to achieve safe therapeutic outcomes. The purpose of this study was to identify the significant covariates for vancomycin clearance and to optimize the dose among surgical patients in Pakistan. Methods: Plasma concentration data of 176 samples collected from 58 surgical patients treated with vancomycin were used in this study. A population pharmacokinetic model was developed on NONMEM^® using plasma concentration-time data. The effect of all available covariates was evaluated on the pharmacokinetic parameters of vancomycin by stepwise covariate modeling. The final model was evaluated using bootstrap, goodness-of-fit plots, and visual predictive checks. Results: The pharmacokinetics of vancomycin followed a one-compartment model with first-order elimination. The vancomycin clearance (CL) and volume of distribution (Vd) were 2.45 L/h and 22.6 l, respectively. Vancomycin CL was influenced by creatinine clearance (CRCL) and body weight of the patients; however, no covariate was significant for its effect on the volume of distribution. Dose tailoring was performed by simulating dosage regimens at a steady state based on the CRCL of the patients. The tailored doses were 400, 600, 800, and 1,000 mg for patients with a CRCL of 20, 60, 100, and 140 ml/min, respectively. Conclusion: Vancomycin CL is influenced by CRCL and body weight of the patient. This model can be helpful for the dose tailoring of vancomycin based on renal status in Pakistani patients.

An Update on Population Pharmacokinetic Analyses of Vancomycin, Part II: In Pediatric Patients

Vancomycin is widely used in pediatric patients, however, large inter- and intraindividual variability are observed in vancomycin pharmacokinetics, affecting proper therapeutic monitoring. This review aimed at providing a comprehensive synthesis of the population pharmacokinetic models of vancomycin in pediatric patients and identifying potential factors responsible for the variability observed in various subpopulations. We conducted a literature search of the PubMed and EMBASE databases to obtain population pharmacokinetic studies for vancomycin published between January 2011 and January 2020, which resulted in a total of 33 studies. Vancomycin pharmacokinetics were generally characterized using a one-compartment model (n = 27), while a two-compartment model was used in six studies. The median (interquartile range) of the typical vancomycin clearance (CL) and the total volume of distribution adjusted to the median or mean body weight of the respective study was 0.103 L/h/kg (0.071-0.125) and 0.64 L/kg (0.59-1.03), respectively. Median weight-adjusted CL between different child age groups, such as infants and adolescents, did not appear to vary significantly, although the sample size for many age groups was very small. Examples of the conditions with relatively abnormal vancomycin pharmacokinetic values include renal insufficiency, sepsis, hematological and solid malignancy, and hypothermia treatment. Factors influencing pediatric vancomycin pharmacokinetics after adjusting for size and maturation include various renal function descriptors and some case-specific variables such as dialysate flow rate, ultrafiltrate output, and hypothermia. This review was able to document possible variables explaining the high variability observed in certain subpopulations and contrast vancomycin pharmacokinetics in different pediatric subpopulations.

Pharmacokinetics of Vancomycin in Pediatric Patients Receiving Intermittent Hemodialysis or Hemodiafiltration

INTRODUCTION

Vancomycin is a common antibiotic used to treat hemodialysis (HD) or hemodiafiltration (HDF)-related infections in pediatric patients, but optimal dosing remains unknown. This is the first observational study to characterize the pharmacokinetics and evaluate dosing of vancomycin in this population.

METHODS

Eligible patients received IV vancomycin 10 mg/kg per dose postdialysis followed by a series of serum vancomycin concentrations collected before, immediately after, 1 hour after, and 4 hours after dialysis. The pharmacokinetic parameters were estimated using 1- and 2-compartment models and a nonlinear least-squares algorithm.

RESULTS

Among 42 vancomycin courses in 16 patients, 1 compartment model had the best fit for observed data. The net drug removal was 43 ± 13% (39% for HD and 50% for HDF) from an average 3-hour HD/HDF session. The mean elimination constant was 0.28 h-1 (standard deviation [SD], 0.11 h-1) during the intradialytic period compared with 0.0049 h-1 (SD, 0.004 h-1) when off dialysis. The mean volume of distribution was 0.65 (SD, 0.19) L/kg. Duration of dialysis session and mode of dialysis (HD vs. HDF) were significant predictors of vancomycin pharmacokinetic parameters. Half-life was shorter for HDF compared with HD (2.1 vs. 3.5 hours).

CONCLUSIONS

Based on the simulations, an initial vancomycin dose of 10 mg/kg per dose and redosing postdialysis was optimal to achieve a vancomycin concentration range of 5 to 12 mg/L at 4 hours postdialysis and 24-hour area under the curve over minimum inhibitory concentration of ≥400 hours. Therapeutic drug monitoring is necessary to account for residual variability in vancomycin elimination in pediatric patients receiving HD/HDF.

Systematic external evaluation of reported population pharmacokinetic models of vancomycin in Chinese children and adolescents

WHAT IS KNOWN AND OBJECTIVES

Various population pharmacokinetic (PopPK) models for vancomycin in children and adolescents have been constructed to optimize the therapeutic regimen of vancomycin. However, little is known about their predictive performance when extrapolated to different clinical centres. Therefore, the aim of this study was to externally validate the predictability of vancomycin PopPK model when extrapolated to different clinical centres and verify its applicability in an independent data set.

METHODS

The published models were screened from the literature and evaluated using an external data set of a total of 451 blood concentrations of vancomycin measured in 220 Chinese paediatric patients. Prediction- and simulation-based diagnostics and Bayesian forecasting were performed to evaluate the predictive performance of the models.

RESULTS

Ten published PopPK models were assessed. Prediction-based diagnostics showed that none of the investigated models met all the standards (median prediction error (MDPE) ≤ ±20%, median absolute prediction error (MAPE) ≤30%, PE% within ±20% (F₂₀ ) ≥35% and PE% within ±30% (F₃₀ ) ≥50%), indicating unsatisfactory predictability. In simulation-based diagnostics, both the visual predictive checks (VPC) and the normalized prediction distribution error (NPDE) indicated misspecification in all models. Bayesian forecasting results showed that the accuracy and precision of individual predictions could be significantly improved with one or two prior observations, but frequent monitoring might not be necessary in the clinic, since Bayesian forecasting identified that greater number of samples did not significantly improve the predictability. Model 3 established by Moffett et al showed better predictability than other models.

WHAT IS NEW AND CONCLUSION

The 10 published models performed unsatisfactorily in prediction- and simulation-based diagnostics; none of the published models was suitable for designing the initial dosing regimens of vancomycin. Pharmacokinetic characteristics and covariates, such as weight, renal function, age and underlying disease should be taken into account when extrapolating the vancomycin model. Bayesian forecasting combined with therapeutic drug monitoring based on model 3 can be used to adjust vancomycin dosing regimens.

Pharmacokinetic and Pharmacodynamic Optimization of Antibiotic Therapy in Cystic Fibrosis Patients: Current Evidences, Gaps in Knowledge and Future Directions

Antibiotic therapy is one of the main treatments for cystic fibrosis (CF). It aims to eradicate bacteria during early infection, calms down the inflammatory process, and leads to symptom resolution of pulmonary exacerbations. CF can modify both the pharmacokinetic (PK) and pharmacodynamic (PD) profiles of antibiotics, therefore specific PK/PD endpoints should be determined in the context of CF. Currently available data suggest that optimal PK/PD targets cannot be attained in sputum with intravenous aminoglycosides. Continuous infusion appears preferable for β-lactam antibiotics, but optimal concentrations in sputum are unlikely to be reached, with some possible exceptions such as meropenem and ceftolozane. Usual doses are likely suboptimal for fluoroquinolones and linezolid, whereas daily doses of 45-60 mg/kg and 200 mg could be convenient for vancomycin and doxycycline, respectively. Weekly azithromycin doses of 22-30 mg/kg could also be appropriate for its anti-inflammatory effect. The difficulty with achieving optimal concentrations supports the use of combined treatments and the inhaled administration route, as very high local concentrations, concomitantly with low systemic exposure, can be obtained with the inhaled route for aminoglycosides, colistin, and fluoroquinolones, thus minimizing the risk of toxicity.

Population Pharmacokinetics Modeling of Vancomycin Among Chinese Infants With Normal and Augmented Renal Function

There have been good amounts of population pharmacokinetics (PPK) models of vancomycin for Chinese pediatric patients, but none of them had a special focus on modeling infant population with different levels of renal function. Since renal function variability is prominent among infant population and the clearance (CL) of vancomycin is heavily related to renal excretion, it is important to establish precise PPK models based on individual renal function levels. We employed a PPK approach to develop three models of vancomycin in parallel for Chinese pediatric patients with normal renal function [estimated glomerular filtration rate (eGFR) between 30 and 86 ml/min/1.73 m², Model 1], with augmented renal function (eGFR ≥ 86 ml/min/1.73 m², Model 2), or with all levels of renal function (Model 3). Three one-compartment models with first-order elimination kinetics were established. The predictive ability of Model 1 and Model 2 among each certain population is comparable with that of Model 3 with no statistical difference. Our study revealed that among the infant population with augmented renal function, only body weight was included as a covariate, which indicated that for an infant whose eGFR ≥ 86 ml/min/1.73 m², taking blood sample is not compulsory for predicting vancomycin blood concentration, which avoids unnecessary injury to vulnerable infants.

The pharmacokinetics of antibiotics in cystic fibrosis

INTRODUCTION

Dosing of antibiotics in people with cystic fibrosis (CF) is challenging, due to altered pharmacokinetics, difficulty of lung tissue penetration, and increasing presence of antimicrobial resistance.

AREAS COVERED

The purpose of this work is to critically review original data as well as previous reviews and guidelines on pharmacokinetics of systemic and inhaled antibiotics in CF, with the aim to propose strategies for optimization of antibacterial therapy in both children and adults with CF.

EXPERT OPINION

For systemic antibiotics, absorption is comparable in CF patients and non-CF controls. The volume of distribution (Vd) of most antibiotics is similar between people with CF with normal body composition and healthy individuals. However, there are a few exceptions, like cefotiam and tobramycin. Many antibiotic class-dependent changes in drug metabolism and excretion are reported, with an increased total body clearance for ß-lactam antibiotics, aminoglycosides, fluoroquinolones, and trimethoprim. We, therefore, recommend following class-specific guidelines for CF, mostly resulting in higher dosages per kg bodyweight in CF compared to non-CF controls. Higher local antibiotic concentrations in the airways can be obtained by inhalation therapy, with which eradication of bacteria may be achieved while minimizing systemic exposure and risk of toxicity.

Comparison of Vancomycin Pharmacokinetics in Cystic Fibrosis Patients Pre and Post-lung Transplant

Background:

Vancomycin is commonly used to treat acute cystic fibrosis (CF) exacerbations associated with methicillin-resistant Staphylococcus aureus (MRSA). Multiple studies have demonstrated pharmacokinetic differences of antimicrobials in the CF population. Very little data exist regarding pharmacokinetics postlung transplant, but 2 studies have noted changes in tobramycin pharmacokinetics. No such studies exist evaluating vancomycin in CF patients postlung transplant.

Methods:

A retrospective cohort review of CF patients who underwent lung transplantation and received vancomycin pre- and posttransplant was conducted. CF patients who underwent transplant between 2007 and 2016 at 4 medical centers throughout the United States were included. The primary endpoint was the change in elimination rate constant. The secondary endpoints were subgroup analyses of patients grouped by age, time posttransplant, and number of nephrotoxic medications.

Results:

A total of 25 patients were included, of which just under half were pediatric. Patients were significantly older and heavier posttransplant and had higher serum creatinine and number of nephrotoxic medications. The change in elimination rate constant from pre- to posttransplant was −0.50 hr⁻¹ which was statistically significant (P < .001). This significant decrease was consistent among all subgroups of patients evaluated with the exception of pediatric patients.

Conclusion:

Vancomycin pharmacokinetics are significantly altered in CF patients in the posttransplant setting as evidenced by a decrease in elimination rate constant. This decrease may be related to a decrease in renal clearance and higher numbers of nephrotoxic medications posttransplant. Regardless, pretransplant vancomycin regimens may not predict appropriate posttransplant regimens.

Desired vancomycin trough concentration to achieve an AUC0-24 /MIC ≥400 in Chinese children with complicated infectious diseases

A vancomycin steady-state trough concentration (C_min ) of 15-20 mg/L is recommended for achieving a ratio of the 24-hour area under the curve to the minimum inhibitory concentration (AUC_0-24 /MIC) of ≥400 in adults. Since few paediatric data are available, our objectives were to (a) measure the pharmacokinetic indices of vancomycin and (b) determine the correlation between C_min and AUC_0-24 /MIC in paediatric patients. Population-based pharmacokinetic modelling was performed for paediatric patients to estimate the individual parameters. The relationship between C_min and the calculated AUC_0-24 /MIC was explored using linear regression and a probabilistic framework. A sensitivity analysis was also conducted using Monte Carlo simulations. Body-weight significantly influenced the pharmacokinetics of vancomycin. Based on real data and simulations, C_min ranges of 5.0-5.9 and 9.0-12.9 mg/L were associated with AUC_0-24 /MIC ≥400 for MIC values of ≤0.5 and ≤1 mg/L, respectively. Vancomycin regimens of 10 and 15 mg/kg every 6 hours achieved a C_min of 5.0-5.9 mg/L and AUC_0-24 /MIC ≥400 in >90% of the children when MIC was ≤0.5 mg/L. At a MIC of ≤1 mg/L, vancomycin at 15 mg/kg every 6 hours achieved C_min of 9.0-12.9 mg/L and AUC_0-24 /MIC ≥400 in 2.0- and 1.6-fold as many children compared to a dose of 10 mg/kg every 6 hours, respectively. Vancomycin C_min values of 5.0-12.9 mg/L were strongly predictive of achieving AUC_0-24 /MIC ≥400, and rational dosing regimens of 10-15 mg/kg q6h were required in paediatric patients, depending on the pathogen.

State of the art in cystic fibrosis pharmacology-Optimization of antimicrobials in the treatment of cystic fibrosis pulmonary exacerbations: I. Anti-methicillin-resistant Staphylococcus aureus (MRSA) antibiotics

Acute pulmonary exacerbations (APE) are a complication of cystic fibrosis (CF) and are associated with morbidity and mortality. Methicillin-resistant Staphylococcus aureus (MRSA) is one of many organisms that has been detected in the airways of patients with CF. This review provides an evidence-based summary of pharmacokinetic/pharmacodynamic (PK/PD), tolerability, and efficacy studies utilizing anti-MRSA antibiotics (ie, ceftaroline, clindamycin, fluoroquinolone derivatives (ciprofloxacin, levofloxacin), glycopeptide derivatives (telavancin, vancomycin), linezolid, rifampin, sulfamethoxazole/trimethoprim (SMZ/TMP), and tetracycline derivatives (doxycycline, minocycline, tigecycline) in the treatment of APE and identifies areas where further study is warranted. A recent utilization study of antimicrobials for anti-MRSA has shown some CF Foundation accredited care centers and affiliate programs are using doses higher than the FDA-approved doses. Further studies are needed to determine the PK/PD properties in CF patients with clindamycin, minocycline, rifampin, SMZ/TMP, telavancin, and tigecycline; as well as, efficacy and tolerability studies with ciprofloxacin, clindamycin, doxycycline, levofloxacin, minocycline, rifampin, SMZ/TMP, in CF patients with MRSA.

Pharmacokinetic considerations in pediatric pharmacotherapy

Purpose

The changes in physiological functions as children grow and organ systems mature result in pharmacokinetic alterations throughout childhood. These alterations in children result in absorption, distribution, metabolism, and excretion of drugs that are different from those seen in the typical adult diseased population.

Summary

Changes in gastrointestinal motility and gastric pH in neonates and infants affect the absorption rate and bioavailability of drugs. Skin absorption rate and extent can be altered by different skin structures and perfusion in young children. Intramuscular and rectal absorption become less predictable in children due to erratic absorption site perfusion and other factors. Children’s body compositions also differ greatly from that in adults. Water-soluble drugs distribute more extensively in newborns due to larger water content than in older children and adults. Drug elimination and excretion are also affected in pediatric population due to differences in liver and renal function. Immature enzyme development and renal function result in reduced clearance of drugs in young children. There are limited pharmacokinetic data available for many drugs used in children.

Conclusion

Considering the changes in pharmacokinetics in children can help pharmacists optimize the dosing and monitoring of drugs and do the best they can to help this vulnerable population.

Preoperative Vancomycin Administration for Surgical Site Prophylaxis: Plasma and Soft-Tissue Concentrations in Pediatric Neurosurgical and Orthopedic Patients

BACKGROUND

Vancomycin is used for antibiotic prophylaxis in pediatric surgical patients without a complete understanding of plasma and soft-tissue pharmacokinetics. Guidelines recommend incision within 60 minutes after administration; however, tissue vancomycin concentrations at that early time may not be therapeutic. We conducted a study of plasma and skin concentrations in pediatric neurosurgical and orthopedic patients to characterize intraoperative vancomycin pharmacokinetics.

METHODS

Patients (0.1-18.8 years of age) undergoing posterior spinal fusion (n = 30) or ventriculoperitoneal shunt placement (n = 30) received intravenous vancomycin 15 mg/kg (maximum 1000 mg) over 1 hour. Skin was biopsied at incision and skin closure. Blood samples were collected at incision, at 2 and 4 hours intraoperatively, and at closure. Population pharmacokinetic analysis was performed to characterize pharmacokinetic parameter estimates and to develop a model of intraoperative plasma and skin vancomycin concentrations versus time.

RESULTS

Pharmacokinetic analysis included data from 59 subjects, 130 plasma samples, and 107 skin samples. A 2-compartment model, volume of the central (Vc) and volume of the peripheral compartment (V2), proved to have the best fit. Stepwise covariate selection yielded a significant relationship for body surface area on elimination clearance and body weight on V2. Skin vancomycin concentrations rose continuously during surgery. Modeling predicted that equilibration of skin and plasma vancomycin concentrations took ≥5 hours.

CONCLUSIONS

Skin vancomycin concentrations immediately after a preoperative dose are relatively low compared with concentrations at the end of surgery. It may be advisable to extend the time between dose and incision if higher skin concentrations are desired at the start of surgery.

Antimicrobial Treatment of Staphylococcus aureus in Patients With Cystic Fibrosis

Staphylococcus aureus is a ubiquitous human commensal pathogen. It is commonly isolated in cystic fibrosis (CF) patients and is considered one of the main causes of the recurrent acute pulmonary infections and progressive decline in lung function that characterize this inherited life-threatening multisystem disorder. However, the true role of S. aureus in CF patients is not completely understood. The main aim of this narrative review is to discuss the present knowledge of the role of S. aureus in CF patients. Literature review showed that despite the fact that the availability and use of drugs effective against S. aureus have coincided with a significant improvement in the prognosis of lung disease in CF patients, clearly evidencing the importance of S. aureus therapy, how to use old and new drugs to obtain the maximal effectiveness has not been precisely defined. The most important problem remains that the high frequency with which S. aureus is carried in healthy subjects prevents the differentiation of simple colonization from infection. Moreover, although experts recommend antibiotic administration in CF patients with symptoms and in those with persistent detection of S. aureus, the best antibiotic approach has not been defined. All these problems are complicated by the evidence that the most effective antibiotic against methicillin-resistant S. aureus (MRSA) cannot be used in patients with CF with the same schedules used in patients without CF. Further studies are needed to solve these problems and to assure CF patients the highest level of care.

Revising Pediatric Vancomycin Dosing Accounting for Nephrotoxicity in a Pharmacokinetic-Pharmacodynamic Model

This study aimed to suggest an initial pediatric vancomycin dose regimen through population pharmacokinetic-pharmacodynamic modeling. A population pharmacokinetic approach was used to analyze vancomycin concentration-time data from a large pediatric cohort. Pharmacokinetic target attainment for patients with bloodstream isolates was compared with clinical outcome using logistic regression and classification and regression trees. Change in serum creatinine during treatment was used as an indicator of acute nephrotoxicity. Probability of acute kidney injury (50% increase from baseline) or kidney failure (75% increase from baseline) was evaluated using logistic regression. An initial dosing regimen was derived, personalized by age, weight, and serum creatinine, using stochastic simulations. Data from 785 hospitalized pediatric patients (1 day to 21 years of age) with suspected Gram-positive infections were collected. Estimated (relative standard error) typical clearance, volume of distribution 1, intercompartmental clearance, and volume of distribution 2 were (standardized to 70 kg) 4.84 (2.38) liters/h, 39.9 (8.15) liters, 3.85 (17.3) liters/h, and 37.8 (10.2) liters, respectively. While cumulative vancomycin exposure correlated positively with the development of nephrotoxicity (713 patients), no clear relationship between vancomycin area under the plasma concentration-time curve and efficacy was found (102 patients). Predicted probability of acute kidney injury and kidney failure with the optimized dosing regimen at day 5 was 10 to 15% and 5 to 10%, increasing by approximately 50% on day 7 and roughly 100% on day 10 across all age groups. This study presents the first data-driven pediatric dose selection to date accounting for nephrotoxicity, and it indicates that cumulative vancomycin exposure best describes risk of acute kidney injury and acute kidney failure.

Pharmacokinetic Monitoring of Vancomycin in Cystic Fibrosis: Is It Time to Move Past Trough Concentrations?

BACKGROUND

A correlation between vancomycin (VAN) trough concentrations (VTC) and area under the curve (AUC) to minimum inhibitory concentration (MIC) ratio (AUC/MIC) has not been established in children/adolescents with cystic fibrosis (CF). The primary objective of this study was to determine the correlation between measured VTCs and AUC/MIC using population-based pharmacokinetics.

METHODS

A retrospective cohort study of children/adolescents diagnosed with CF, 6 to <18 years of age, treated with VAN for methicillin-resistant Staphylococcus aureus infection was conducted. The relationship between final VTCs and calculated AUC/MIC was assessed using Pearson and Spearman correlations. All tests were 2-tailed with alpha set at 0.05.

RESULTS

Thirty children/adolescents, 7 to 17 years of age (median age 15 year; interquartile range: 9-17 years), were included. The mean final VAN dose was 58.03 ± 18.58 mg/kg/d, and the median final VTC was 12.6 (11-13.6) mg/L. The mean AUC/MIC was 355.34 ± 138.46 (Le model) versus 426.79 ± 178.92 (Stockmann model; P = 0.089). No correlation existed between VTCs and AUC/MIC using either the model by Le (r = 0.140; P = 0.461) or Stockmann (r = 0.115; P = 0.564). Using the Stockmann model, VAN dose (mg/kg/dose) was found to have a strong positive correlation with AUC (r = 0.8874; P < 0.0001) and AUC/MIC (r = 0.7877; P < 0.0001).

CONCLUSIONS

VTCs did not correlate with AUC or AUC/MIC. Further research is needed to determine which estimate of VAN treatment efficacy is most appropriate for children and adolescents with CF infected with methicillin-resistant Staphylococcus aureus.

An Evaluation of Vancomycin Area Under the Curve Estimation Methods for Children Treated for Acute Pulmonary Exacerbations of Cystic Fibrosis Due to Methicillin-Resistant Staphylococcus aureus

The prevalence of pulmonary methicillin-resistant Staphylococcus aureus infections in patients with cystic fibrosis (CF) has increased over the last 2 decades. Two concentrations-a postdistributive and a trough-are currently used to estimate the area under the curve (AUC) of vancomycin, an antibiotic routinely used to treat these infections, to achieve the target AUC/minimum inhibitory concentration of ≥400 mg·h/L in ensuring optimal dosing of this drug. This study evaluated precision and bias in estimating vancomycin AUCs obtained either from a population pharmacokinetic (PK) model by using a single trough concentration or from standard PK equation-based 2-point monitoring approach. AUCs were either obtained from a single trough concentration-fitted model or derived from a model fitted by 2 concentration points. Children ≥2 years of age with CF received intravenous vancomycin at 2 centers from June 2012 to December 2014. A population PK model was developed in Pmetrics to quantify the between-subject variability in vancomycin PK parameters, define the sources of PK variability, and leverage information from the population to improve individual AUC estimates. Twenty-three children with CF received 27 courses of vancomycin. The median age was 12.3 (interquartile range [IQR] 8.5-16.6) years. From the individual vancomycin PK parameter estimates from the population PK model, median AUC was 622 (IQR 529-680) mg·h/L. Values were not significantly different from the AUC calculated using the standard PK equation-based approach (median 616 [IQR 540-663] mg·h/L) (P = .89). A standard PK equation-based approach using 2 concentrations and a population PK model-based approach using a single trough concentration yielded unbiased and precise AUC estimates. Findings suggest that options exist to implement AUC-based pediatric vancomycin dosing in patients with CF. The findings of this study reveal that several excellent options exist for centers to implement AUC-based pediatric vancomycin dosing for patients with CF.

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

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

Ceftaroline pharmacokinetics and pharmacodynamics in patients with cystic fibrosis

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is a prevalent pathogen in patients with cystic fibrosis (CF) associated with increased morbidity. Ceftaroline fosamil is an intravenous (IV) cephalosporin with activity against MRSA. There are minimal data regarding dosing in the CF population. The objective of this study was to determine the pharmacokinetic and pharmacodynamic profile of IV ceftaroline in patients with CF.

METHODS

We conducted a single-center prospective study of children and young adults with CF receiving ceftaroline (15mg/kg IV up to 600mg every 8h) as part of treatment for a CF pulmonary exacerbation between June 2016 and April 2017. Seven patients were enrolled for a total of 10 treatment courses. For each treatment course, up to 8 plasma samples were assayed for ceftaroline using ultra-high performance liquid chromatography with mass spectrometry. Maximum plasma concentration, systemic clearance, and elimination half-life were calculated. The area under the curve (AUC) above the minimum inhibitory concentration (MIC) and the percent time above the MIC (%fT>MIC) were determined for each subject using MICs of 0.5, 1, and 2μg/mL and the measured MIC if available.

RESULTS

The mean (SD) age for the 7 patients was 20.3 (8.0) years. Mean (SD) maximum plasma concentration of ceftaroline was 22.7 (9.6) μg/mL, systemic clearance 7.9 (3.3) L/h, and half-life 1.1 (0.4) hours. Using a MIC of 1 μg/mL, accepted as the MIC 90 of MRSA isolates, AUC above MIC mean (SD) was 53.6 (19.5) μg·h/mL, mean (SD) %fT>MIC was 75.7 (10.4), and all subjects had >60%fT>MIC.

CONCLUSIONS

In this cohort of CF patients, mean ceftaroline half-life was 1.1h, which is notably lower than the general population. The dosing regimen studied, which exceeds the recommended dosing in the non-CF population, was adequate to achieve >60% time above the MIC in all patients.

Vancomycin Dosing and Monitoring in the Treatment of Cystic Fibrosis: Results of a National Practice Survey

OBJECTIVES

Vancomycin is commonly used in patients with cystic fibrosis (CF) to treat acute pulmonary exacerbations, but few guidelines exist to help dose and monitor patients. The objective of this study was to assess vancomycin use and monitoring strategies at Cystic Fibrosis Foundation (CFF)-accredited centers in hopes of developing and implementing vancomycin dosing and monitoring standards.

METHODS

An anonymous national cross-sectional survey of pharmacists affiliated with CFF-accredited pediatric and/or adult centers was performed by using Surveymonkey.com. The survey consisted of 3 sections: (1) CF Center Demographic Information (10 questions); 2) vancomycin use in pediatric CF patients (31 questions); and 3) vancomycin use in adult CF patients (29 questions); it was administered from March 9, 2015, to April 13, 2015.

RESULTS

The survey was completed by 31/69 (45%) pharmacists and 28 (90.3%) reported using vancomycin in the pediatric population. The most common initial starting dose for pediatric patients was 15 mg/kg/dose (57.1%) and every 6 hours was the most common dosing frequency (67.9%). The most common monitoring strategy was collection of a trough concentration (92.9%) with 57.7% of pharmacist targeting a range of 15 to 20 mg/L. The most common initial starting vancomycin dose in adults with CF was 15 mg/kg/dose (61.5%), and initial frequency of every 8 hours (73.1%). The most common monitoring strategy was a trough concentration (96.2%) with 83.3% of pharmacists reporting a goal trough range of 15 to 20 mg/L.

CONCLUSIONS

The most common vancomycin dosing reported was 15 to 20 mg/kg/dose every 6 hours (pediatric) and 15 to 20 mg/kg/dose every 8 to 12 hours (adults). Serum concentrations measured to meet monitoring parameters of trough concentrations of 15 to 20 mg/L, or area under the curve to minimum inhibitory concentration ratio > 400, were the same in both pediatric and adult patients.

Association of Vancomycin Trough Concentration With Response to Treatment for Acute Pulmonary Exacerbation of Cystic Fibrosis

BACKGROUND

Our goal was to determine the relationship between serum vancomycin trough concentrations (VTCs) and changes in pulmonary function among individuals with an acute pulmonary exacerbation (APE) of cystic fibrosis (CF).

METHODS

We included subjects who were ≥6 years of age, were hospitalized for an APE of CF between May 1, 2012, and April 30, 2014, were administered vancomycin for ≥48 hours, and had a history of airway infection with methicillin-resistant Staphylococcus aureus. Pearson correlations were performed to characterize the relationship between VTC and pulmonary function.

RESULTS

The mean final VTC (± standard deviation) was 12.6 ± 3.3 µg/mL; 40 (81.6%) of 49 final VTCs were in the range of 10 to <15 µg/mL. The mean change in forced expiratory volume in 1 second (FEV1) between admission and discharge was 24.5% ± 24.4% (P < .001) of predicted values. Forty-two (85.7%) patients returned to their baseline FEV1. No correlation between the change in FEV1 and VTC (Pearson r = -0.10; P = .49) was identified. Similarly, VTC, daily weight-adjusted vancomycin dose, and vancomycin area under the concentration-time curve normalized to the minimum inhibitory concentration (AUC/MIC) were not significant predictors of change in FEV1 or return to baseline FEV1 on multivariate analysis. One (2%) subject experienced acute kidney injury.

CONCLUSIONS

The majority of patients experienced improvement in pulmonary function and a return to their baseline FEV1 while achieving a VTC in the range of 10 to <15 µg/mL. We were unable to identify a correlation between markers of vancomycin exposure and change in pulmonary function test results. Additional studies are needed to reinforce the efficacy of VTCs of 10 to 15 µg/mL for treating APEs of CF.

Impact of Initial Vancomycin Trough Concentration on Clinical and Microbiological Outcomes of Methicillin-Resistant Staphylococcus aureus Bacteremia in Children

It is important to use vancomycin in a proper manner to ensure optimal drug exposure. Despite extensive use of vancomycin in children, studies on its optimal trough concentration (Ctrough) in the pediatric population remained rare. This retrospective study included children < 18 years old with culture-confirmed methicillin-resistant Staphylococcus aureus (MRSA) bacteremia who were hospitalized in our institute from January 2010 to April 2014. Clinical characteristics, initial vancomycin dose, Ctrough and clinical/microbiological outcomes were retrospectively collected from medical records. Forty-six MRSA bacteremia cases occurring to the patients with a mean age of 22.0 ± 46.9 months were included and all of them were healthcare-associated. Severe diseases requiring intensive care unit (ICU) stay, mechanical ventilation and/or resulting in death were observed in 57.8% (26/45); all-cause 30-day fatality was 11.1% (5/45). An initial Ctrough ≥ 15 μg/mL was achieved in only 4 (8.7%) cases with an average vancomycin dosage of 40.6 ± 7.9 mg/kg/day. Persistent bacteremia at 48 hours after initiation of vancomycin was observed more frequently in children with initial Ctrough < 10 μg/mL than in those with Ctrough ≥ 10 μg/mL (P = 0.032). However, there was no statistically significant difference between the two groups in terms of 30-day mortality and recurrent bacteremia (P = 0.899, and P = 0.754, respectively). Although initial Ctrough may be a useful parameter for minimizing early microbiological failure, it does not predict 30-day fatality or recurrence in pediatric MRSA bacteremia. Further prospective data on vancomycin dosing are needed to find the optimal drug exposure and clarify its impact on clinical outcomes in pediatric populations.

Evaluation of Vancomycin Dosing in Pediatric Cystic Fibrosis Patients

OBJECTIVES

The presence of methicillin-resistant Staphylococcus aureus (MRSA) in cystic fibrosis (CF) patients' sputa is associated with a decline in pulmonary function and increased mortality. Vancomycin is the preferred treatment for MRSA pneumonia in children. No published studies have evaluated the vancomycin dose needed to achieve goal vancomycin trough concentrations (VTCs; 15-20 mg/L) in pediatric patients with CF. The primary objective is to determine whether a vancomycin dosage of 60 mg/kg/day achieves a goal VTC in pediatric CF patients. Secondary objectives include determining the average dosage required to reach a goal VTC and the impact of achieving a goal VTC on estimated glomerular filtration rate (eGFR) and pulmonary function.

METHODS

A retrospective review of pediatric patients with CF who received vancomycin was conducted.

RESULTS

A total of 90 vancomycin treatment courses were analyzed. Standard vancomycin dosing (60 mg/kg/day) achieved goal VTC in 11 courses (12.2%). The mean dosage required to achieve a goal VTC for all courses was 70.6 ± 16.7 mg/kg/day. Patients who achieved goal VTCs were more often older, weighed more, and had higher serum creatinine concentrations at therapy initiation. On average, a dosage of 70.6 mg/kg/day was required to achieve a goal VTC. Despite dosages up to 120 mg/kg/day, no significant changes in renal function occurred. Achieving a goal VTC had no significant impact on eGFR or pulmonary function during therapy.

CONCLUSIONS

Vancomycin dosing of 60 mg/kg/day does not reliably achieve a VTC of 15 to 20 mg/L in pediatric CF patients. Younger CF patients may require higher vancomycin doses.

Correlation of a Vancomycin Pharmacokinetic Model and Trough Serum Concentrations in Pediatric Patients

BACKGROUND

Vancomycin trough concentrations specific to pediatric patients have yet to be validated that achieve an area under the curve (AUC) over 24 hours to minimum inhibitory concentration (MIC) ratio ≥400. The primary objective of this study was to validate a pharmacokinetic model in a pediatric hospital and determine the correlation between a calculated AUC/MIC ratio and measured trough vancomycin concentration.

METHODS

A retrospective evaluation of patients aged 3 months to 18 years prescribed vancomycin at a pediatric hospital between January 2012 and June 2013. The correlation between patient-specific AUC/MIC and measured vancomycin trough concentration was assessed.

RESULTS

Forty pediatric patients with 40 vancomycin trough concentrations and documented Staphylococcus aureus cultures were included in the study. Median age was 8.5 (interquartile range, 2-14.3) years, median weight 28.7 (range, 14-50.2) kg, and mean baseline serum creatinine 0.51 ± 0.3 mg/dL. The mean daily dose of vancomycin prescribed was 58 ± 13.8 mg/kg/d. The mean vancomycin trough concentration was 11 ± 5.5 mcg/mL, and the mean AUC/MIC was 534 ± 373. No correlation was found between trough concentration and AUC/MIC (r = 0.082, p = 0.07).

CONCLUSIONS

This study validates the clinical applicability of a pharmacokinetic model for calculating vancomycin clearance to determine patient-specific AUC over 24 hours in pediatrics. Trough concentrations associated with proposed therapeutic AUC/MIC ratios were lower than reported in the adult population. Further research is needed to determine if AUC/MIC, trough concentration, or both is best for monitoring therapeutic efficacy of vancomycin in pediatrics.

Vancomycin pharmacokinetic models: informing the clinical management of drug-resistant bacterial infections

This review aims to critically evaluate the pharmacokinetic literature describing the use of vancomycin in the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections. Guidelines recommend that trough concentrations be used to guide vancomycin dosing for the treatment of MRSA infections; however, numerous in vitro, animal model and clinical studies have demonstrated that the therapeutic effectiveness of vancomycin is best described by the area under the concentration versus time curve (AUC) divided by the minimum inhibitory concentration (MIC) of the infecting organism (AUC/MIC). Among patients with lower respiratory tract infections, an AUC/MIC ≥400 was associated with a superior clinical and bacteriological response. Similarly, patients with MRSA bacteremia who achieved an Etest AUC/MIC ≥320 within 48 h were 50% less likely to experience treatment failure. For other patient populations and different clinical syndromes (e.g., children, the elderly, patients with osteomyelitis, etc.), pharmacokinetic/pharmacodynamic studies and prospective clinical trials are needed to establish appropriate therapeutic targets.

Development of an optimal sampling schedule for children receiving ketamine for short-term procedural sedation and analgesia

BACKGROUND

Intravenous racemic ketamine is commonly administered for procedural sedation, although few pharmacokinetic studies have been conducted among children. Moreover, an optimal sampling schedule has not been derived to enable the conduct of pharmacokinetic studies that minimally inconvenience study participants.

METHODS

Concentration-time data were obtained from 57 children who received 1-1.5 mg·kg(-1) of racemic ketamine as an intravenous bolus. A population pharmacokinetic analysis was conducted using nonlinear mixed effects models, and the results were used as inputs to develop a D-optimal sampling schedule.

RESULTS

The pharmacokinetics of ketamine were described using a two-compartment model. The volume of distribution in the central and peripheral compartments were 20.5 l∙70 kg(-1) and 220 l∙70 kg(-1), respectively. The intercompartmental clearance and total body clearance were 87.3 and 87.9 l·h(-1) ∙70 kg(-1), respectively. Population parameter variability ranged from 34% to 98%. Initially, blood samples were drawn on 3-6 occasions spanning a range of 14-152 min after dosing. Using these data, we determined that four optimal sampling windows occur at 1-5, 5.5-7.5, 10-20, and 90-180 min after dosing. Monte Carlo simulations indicated that these sampling windows produced precise and unbiased ketamine pharmacokinetic parameter estimates.

CONCLUSION

An optimal sampling schedule was developed that allowed assessment of the pharmacokinetic parameters of ketamine among children requiring short-term procedural sedation.

Antibiotic Management of Methicillin-Resistant Staphylococcus aureus–Associated Acute Pulmonary Exacerbations in Cystic Fibrosis

Objective: To review the treatment of methicillin-resistant Staphylococcus aureus (MRSA)–associated acute pulmonary exacerbations (APEs) in cystic fibrosis (CF). Data Sources: A search of PubMed, MEDLINE, Cochrane Library and Clinicaltrials.gov databases through November 2014 was conducted using the search terms Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, pulmonary exacerbations, and cystic fibrosis. Study Selection and Data Extraction: All English-language research articles, case reports, and case series were evaluated. A total of 185 articles were identified related to MRSA and CF; 30 articles that studied treatments of MRSA APE in CF were included. Data Synthesis: The persistent presence of MRSA in the respiratory tract of patients with CF has been associated with higher morbidity and an increased risk of death. Limited clinical data exist supporting the efficacy of any specific antimicrobial currently available for the treatment of APE secondary to MRSA. Conclusions: Data extrapolated from other populations suggest that vancomycin and linezolid are appropriate first-line treatment options for the treatment of APE secondary to MRSA. Second-line options include doxycycline or minocycline and trimethoprim/sulfamethoxazole, each of which may be useful in patients coinfected with other respiratory pathogens, for which they may provide overlapping coverage. Ceftaroline and ceftobiprole are newer antibiotics that appear to have a potential role in the treatment of APE in CF, but the latter is not currently available to the US market. Although potentially useful, clindamycin is limited by high rates of resistance, telavancin is limited by its toxicity profile, and tigecycline is limited by a lack of demonstrated efficacy for infections that are similar to that seen in the CF population. Studies investigating the clinical utility of the above-cited antibiotics for APE in CF secondary to MRSA are desperately needed to broaden the treatment armamentarium for this medical condition.

Advances in pediatric pharmacology, therapeutics, and toxicology

In the United States, passage of the FDASIA legislation made BPCA and PREA permanent, no longer requiring reauthorization every 5 years. This landmark legislation also stressed the importance of performing clinical trials in neonates when appropriate. In Europe the Pediatric Regulation, which went into effect in early 2007, also provides a framework for expanding pediatric clinical research. Although much work remains, as a result of greater regulatory guidance more pediatric data are reaching product labels.