Population pharmacokinetics of vancomycin in obesity: Finding the optimal dose for (morbidly) obese individuals

Developing Parametric and Nonparametric Models for Model-Informed Precision Dosing: A Quality Improvement Effort in Vancomycin for Patients With Obesity

BACKGROUND

Both parametric and nonparametric methods have been proposed to support model-informed precision dosing (MIPD). However, which approach leads to better models remains uncertain. Using open-source software, these 2 statistical approaches for model development were compared using the pharmacokinetics of vancomycin in a challenging subpopulation of class 3 obesity.

METHODS

Patients on vancomycin at the University of Vermont Medical Center from November 1, 2021, to February 14, 2023, were entered into the MIPD software. The inclusion criteria were body mass index (BMI) of at least 40 kg/m 2 and 1 or more vancomycin levels. A parametric model was created using nlmixr2/NONMEM, and a nonparametric model was created using Pmetrics. Then, a priori and a posteriori predictions were evaluated using the normalized root mean squared error (nRMSE) for precision and the mean percentage error (MPE) for bias. The parametric model was evaluated in a simulated MIPD context using an external validation dataset.

RESULTS

In total, 83 patients were included in the model development, with a median age of 56.6 years (range: 24-89 years), and a median BMI of 46.3 kg/m 2 (range: 40-70.3 kg/m 2 ). Both parametric and nonparametric models were 2-compartmental, with creatinine clearance and fat-free mass as covariates to clearance and volume parameters, respectively. The a priori MPE and nRMSE for the parametric versus nonparametric models were -6.3% versus 2.69% and 27.2% versus 30.7%, respectively. The a posteriori MPE and RMSE were 0.16% and 0.84%, and 13.8% and 13.1%. The parametric model matched or outperformed previously published models on an external validation dataset (n = 576 patients).

CONCLUSIONS

Minimal differences were found in the model structure and predictive error between the parametric and nonparametric approaches for modeling vancomycin class 3 obesity. However, the parametric model outperformed several other models, suggesting that institution-specific models may improve pharmacokinetics management.

Dosing and Exposure of Vancomycin With Continuous Infusion: A Retrospective Study

Vancomycin continuous infusion (CI) has suggested benefits over intermittent infusion: reduced nephrotoxicity, higher target attainment, and simpler therapeutic drug monitoring (TDM). Empiric dosing regimens range from 30-60 mg/kg/day and it is unclear which regimen results in optimal exposure. This study evaluates whether a dosing regimen of 45 mg/kg/day after a 20 mg/kg loading dose for patients with estimated glomerular filtration rate (eGFR) ≥ 50 mL/min results in adequate exposure. We retrospectively analyzed plasma concentrations from patients treated with vancomycin CI as routine clinical care between February and October 2021. Patients under 18 years old, with renal replacement therapy, reduced creatinine clearance (Chronic Kidney Disease Epidemiology Collaboration < 50 mL min/1.73 m2) or outpatient antibiotic therapy were excluded. Dose, renal function, and blood draw procedures were assessed for each measured vancomycin sample. Initially, 121 samples were included. Subsequently, 7 samples, 6 of which with concentrations ≥ 40 mg/L, were verified to be incorrectly drawn and excluded. With doses of 40-50 mg/kg/day concentrations ranged from 18.4-61.0 mg/L. Only 25% were within the target window of 17-25 mg/L and 15% were ≥ 40 mg/L. Supratherapeutic concentrations were observed in 89% of samples from patients dosed 40-60 mg/kg/day with eGFR 50-80 mL/min. Concluding, an empiric dosing regimen of 45 mg/kg results in too high vancomycin exposure and thus we recommend lower doses and differentiation according to renal function. Additionally, when measuring concentrations over 40 mg/L incorrect sampling must be excluded before dose adjustment and the large variability in exposure between patients, warrants the need for swift TDM.

Impact of Obesity on Hepatic Drug Clearance: What are the Influential Variables?

Drug clearance in obese subjects varies widely among different drugs and across subjects with different severity of obesity. This study investigates correlations between plasma clearance (CLp) and drug- and patient-related characteristics in obese subjects, and evaluates the systematic accuracy of common weight-based dosing methods. A physiologically-based pharmacokinetic (PBPK) modeling approach that uses recent information on obesity-related changes in physiology was used to simulate CLp for a normal-weight subject (body mass index [BMI] = 20) and subjects with various severities of obesity (BMI 25-60) for hypothetical hepatically cleared drugs with a wide range of properties. Influential variables for CLp change were investigated. For each drug and obese subject, the exponent that yields perfect allometric scaling of CLp from normal-weight subjects was assessed. Among all variables, BMI and relative changes in enzyme activity resulting from obesity proved highly correlated with obesity-related CLp changes. Drugs bound to α1-acid glycoprotein (AAG) had lower CLp changes compared to drugs bound to human serum albumin (HSA). Lower extraction ratios (ER) corresponded to higher CLp changes compared to higher ER. The allometric exponent for perfect scaling ranged from -3.84 to 3.34 illustrating that none of the scaling methods performed well in all situations. While all three dosing methods are generally systematically accurate for drugs with unchanged or up to 50% increased enzyme activity in subjects with a BMI below 30 kg/m2, in any of the other cases, information on the different drug properties and severity of obesity is required to select an appropriate dosing method for individuals with obesity.

External Validation of Obese/Critically Ill Vancomycin Population Pharmacokinetic Models in Critically Ill Patients Who Are Obese

Obesity combined with critical illness might increase the risk of acquiring infections and hence mortality. In this patient population the pharmacokinetics of antimicrobials vary significantly, making antimicrobial dosing challenging. The objective of this study was to assess the predictive performance of published population pharmacokinetic models of vancomycin in patients who are critically ill or obese for a cohort of critically ill patients who are obese. This was a multi-center retrospective study conducted at 2 hospitals. Adult patients with a body mass index of ≥30 kg/m2 were included. PubMed was searched for published population pharmacokinetic studies in patients who were critically ill or obese. External validation was performed using Monolix software. A total of 4 models were identified in patients who were obese and 5 models were identified in patients who were critically ill. In total, 138 patients who were critically ill and obese were included, and the most accurate models for these patients were the Goti and Roberts models. In our analysis, models in patients who were critically ill outperformed models in patients who were obese. When looking at the most accurate models, both the Goti and the Roberts models had patient characteristics similar to ours in terms of age and creatinine clearance. This indicates that when selecting the proper model to apply in practice, it is important to account for all relevant variables, besides obesity.

Documentation of the Patient Characteristics Morbid Obesity and Bariatric Surgery in the Hospital Information System and the Influence on the Number of Medication-Related Problems

BACKGROUND

As a result of pharmacokinetic changes, individuals with morbid obesity and/or with bariatric surgery may require dose adjustments, additional monitoring or medication should be avoided. Clinical decision support (CDS) may provide automated alerts enabling correct prescribing but requires documentation of these patient characteristics in the Hospital Information System (HIS) to prevent medication-related problems (MRPs).

OBJECTIVE

The primary objective is to determine the proportion of patients with documentation of the patient characteristics morbid obesity and bariatric surgery in the HIS. The secondary objective is to compare the proportion of patients with an MRP in the group with versus without documentation. Also, the type and severity of MRPs and the medication involved are determined.

METHODS

A prospective cohort study was performed. Patients admitted to the hospital were identified as morbidly obese and/or with bariatric surgery. In the identified patients, the proportion of patients with documentation of the patient characteristics in the HIS was evaluated as primary outcome. Subsequently, patient records were reviewed for MRPs, which were categorized and associated medication was registered. For the primary objective, descriptive statistics was used. For the secondary outcome, the Fisher's exact test was used.

RESULTS

In 43 (21.4%, 95% confidence interval [CI]: 15.7%-27.1%) of 201 included patient (113 morbid obesity, 70 bariatric surgery and 18 both), the patient characteristics were documented. An MRP occurred in 2.3% versus 13.9% (P = 0.032) of patients with and without documentation, respectively. The most common MRP was underdosing in morbid obesity, while in patients with bariatric surgery it was prescription of contra-indicated medication.

CONCLUSION AND RELEVANCE

The proportion of patients with documentation of the patient characteristics bariatric surgery and/or morbid obesity in the HIS is low, which appears to be associated with more MRPs. To improve medication safety, it is important to document these patient characteristics.

How to Dose Vancomycin in Overweight and Obese Patients with Varying Renal (Dys)function in the Novel Era of AUC 400-600 mg·h/L-Targeted Dosing

BACKGROUND AND OBJECTIVE

The latest vancomycin guideline recommends area under the curve (AUC)-targeted dosing and monitoring for efficacy and safety. However, guidelines for AUC-targeted starting dosing in patients with obesity and/or renal insufficiency are currently lacking. This study quantifies the pharmacokinetics (PK) of vancomycin in this population and provides AUC-targeted dosing recommendations.

METHODS

Vancomycin concentrations (n = 1188) from therapeutic drug monitoring of 210 overweight and obese patients with varying degrees of renal (dys)function from the ward (74.8%) and intensive care unit (ICU, 25.2%) were pooled with published rich concentration-time data (n = 207) from 20 (morbidly) obese subjects undergoing bariatric surgery. A population model was developed using NONMEM 7.4. Stochastic simulations were performed to design dosing guidelines targeting an AUC24 between 400-600 mg·h/L.

RESULTS

Vancomycin clearance (CL) was found to increase linearly with total bodyweight and with renal function (CKD-EPI) in a power relation. Additionally, CL proved 15.5% lower in ICU patients. Our model shows that, to reach the target AUC between 400 and 600 mg·h/L in the first 48 h, two loading doses are required for both continuous infusion and intermittent dosing regimens. Maintenance doses were found to require adjustment for total bodyweight, renal function, and ICU admission status. With this guideline, the median AUC24 is well within the target from the start of the treatment onwards.

CONCLUSIONS

To achieve safe and effective vancomycin exposure for maintenance doses in overweight and obese patients, renal function, total bodyweight, and ICU admission status should be taken into account.

TRIAL REGISTRATION

The AMIGO trial was registered in the Dutch Trial Registry [NTR6058].

Patients with Obesity Should be Recognised as a Special Patient Population During Drug Development of Antibacterial and Antifungal Agents; A Call to Action

Individuals with obesity are at increased risk of developing infectious diseases. Timely administration of an effective dose of an antimicrobial agent is paramount to safeguard optimal therapy. For this purpose, special patient populations at risk for altered exposure such as renal or hepatic impairment are studied during drug development. Strikingly, there is no such evaluation in individuals with obesity despite a potential influence on exposure and a global obesity prevalence of 13 %. Optimal clinical decision making in patients with obesity is impossible without prior study of the drug of interest in this population. This statement is strengthened by an evaluation of 19 antimicrobial agents that showed tremendous variability in the influence of weight on clearance. In contrast to patient with renal or hepatic impairment who are mainly at risk of overexposure, individuals with obesity can be at risk of both under- and overexposure. Gaining knowledge on the influence of body weight on clearance during early phases of drug development may allow for optimisation of other phases of research, potentially increasing success rate of the drug, and can provide clinicians with vital information as soon as the drug reaches the market. Antimicrobial therapy should be tailored to obesity-related (patho)physiological changes and to reach this goal, obese individuals should be studied during drug development.

The Importance of Assessing Drug Pharmacokinetics and Pharmacodynamics in the Obese Population During Drug Development

Obesity remains a US national health crisis and a growing concern worldwide. Concerningly, individuals who are obese are at an increased risk for comorbid diseases that include, but are not limited to, hypertension, diabetes, cardiovascular disease, and cancer. Beyond the risk for developing these conditions, obesity may also impact the pharmacological activity of the therapies being used to treat them and other disease states. The pharmacokinetics (PK), pharmacodynamics (PD), safety, and efficacy of therapies, both currently marketed and under clinical development, may be directly impacted by the physiological alterations that occur secondary to the occurrence of chronic excess body weight. The increased prevalence of this disease should not be ignored. Both private and federal institutions involved in drug research and development should consider, as appropriate, a greater inclusion of individuals who are obese in clinical trials throughout the entirety of drug development, and leverage the available PK, PD, safety, and efficacy data to make more informed dosing recommendations.

Comprehensive guidance for antibiotic dosing in obese adults: 2022 update

Drug dosing in obese patients continues to be challenging due to a lack of high-quality evidence to guide dosing recommendations. We first published guidance for antibiotic dosing in obese adults in 2017, in which we critically reviewed articles identified from a broad search strategy to develop dosing recommendations for 35 antimicrobials. In this updated narrative review, we searched Pubmed, Web of Science, and the Cochrane Library using Medical Subject Headings including anti-infectives, specific generic antimicrobial names, obese, pharmacokinetics, and others. We reviewed 393 articles, cross-referenced select cited references, and when applicable, referenced drug databases, package inserts, and clinical trial data to update dosing recommendations for 41 antimicrobials. Most included articles were pharmacokinetic studies, other less frequently included articles were clinical studies (mostly small, retrospective), case reports, and very rarely, guidelines. Pharmacokinetic changes are frequently reported, can be variable, and sometimes conflicting in this population, and do not always translate to a documented difference in clinical outcomes, yet are used to inform dosing strategies. Extended infusions, high doses, and therapeutic drug monitoring remain important strategies to optimize dosing in this population. Additional studies are needed to clinically validate proposed dosing strategies, clarify optimal body size descriptors, dosing weight scalars, and estimation method of renal function in obese patients.

A Brief Review of Pharmacokinetic Assessments of Vancomycin in Special Groups of Patients with Altered Pharmacokinetic Parameters

Vancomycin is considered the drug of choice against many Gram-positive bacterial infections. Therapeutic drug monitoring (TDM) is essential to achieve an optimum clinical response and avoid vancomycin-induced adverse reactions including nephrotoxicity. Although different studies are available on vancomycin TDM, still there are controversies regarding the selection among different pharmacokinetic parameters including trough concentration, the area under the curve to minimum inhibitory concentration ratio (AUC24h/MIC), AUC of intervals, elimination constant, and vancomycin clearance. In this review, different pharmacokinetic parameters for vancomycin TDM have been discussed along with corresponding advantages and disadvantages. Also, vancomycin pharmacokinetic assessments are discussed in patients with altered pharmacokinetic parameters including those with renal and/or hepatic failure, critically ill patients, patients with burn injuries, intravenous drug users, obese and morbidly obese patients, those with cancer, patients undergoing organ transplantation, and vancomycin administration during pregnancy and lactation. An individualized dosing regimen is required to guarantee the optimum therapeutic responses and minimize adverse reactions including acute kidney injury in these special groups of patients. According to the pharmacoeconomic data on vancomycin TDM, pharmacokinetic assessments would be cost-effective in patients with altered pharmacokinetics and are associated with shorter hospitalization period, faster clinical stability status, and shorter courses of inpatient vancomycin administration.

Dose optimization of vancomycin in obese patients: A systematic review

Background: Dose optimization of vancomycin plays a substantial role in drug pharmacokinetics because of the increased incidence of obesity worldwide. This systematic review was aimed to highlight the current dosing strategy of vancomycin among obese patients. Methods: This systematic review was in concordance with Preferred Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. The literature search was carried out on various databases such as Scopus, PubMed/MEDLINE, ScienceDirect and EMBASE using Keywords and MeSH terms related to vancomycin dosing among obese patients. Google Scholar was also searched for additional articles. The English language articles published after January, 2000 were included in this study. The quality of the study was assessed using different assessment tools for cohort, and case reports. Results: A total of 1,029 records were identified. After screening, 18 studies were included for the final review. Of total, twelve studies are retrospective and remaining six are case-control studies. A total of eight studies were conducted in pediatrics while remaining studies were conducted in adult population. Most of the studies reported the dosing interval every 6-8 h. Differences in target trough concentration exist with respect to target ranges. The administration of loading dose (20-25 mg/kg) followed by maintenance dose (15-25 mg/kg) of vancomycin is recommended in adult patients to target therapeutic outcomes. Moreover, a dose of 40-60 mg/kg/day appears appropriate for pediatric patients. Conclusion: The initial dosing of vancomycin based on TBW could be better predictor of vancomycin trough concentration. However, the clinical significance is uncertain. Therefore, more studies are needed to evaluate the dosing strategy of vancomycin in overweight or obese patients.

Drug pharmacokinetics in the obese population: challenging common assumptions on predictors of obesity-related parameter changes

INTRODUCTION

Obesity is associated with many physiological changes. We review available evidence regarding five commonly accepted assumptions to a priori predict the impact of obesity on drug pharmacokinetics (PK).

AREAS COVERED

The investigated assumptions are: 1) lean body weight is the preferred descriptor of clearance and dose adjustments; 2) volume of distribution increases for lipophilic, but not for hydrophilic drugs; 3) CYP-3A4 activity is suppressed and UGT activity is increased, implying decreased and increased dose requirements for substrates of these enzyme systems, respectively; 4) glomerular filtration rate is enhanced, necessitating higher doses for drugs cleared through glomerular filtration; 5) drug dosing information from obese adults can be extrapolated to obese adolescents.

EXPERT OPINION

Available literature contradicts, or at least limits the generalizability, of all five assumptions. Clinical studies should focus on quantifying the impact of duration and severity of obesity on drug PK in adults and adolescents, and also include oral bioavailability and pharmacodynamics in these studies. Physiologically-based PK approaches can be used to predict PK changes for individual drugs, but can also be used to define in general terms based on patient characteristics and drug properties, when certain assumptions can or cannot be expected to be systematically accurate.

Vancomycin therapeutic drug monitoring in patients on continuous renal replacement therapy: a retrospective study

Objectives

This study aimed to investigate vancomycin therapeutic drug monitoring (TDM) in patients on continuous renal replacement therapy (CRRT) and explore the risk factors for exceeding the target concentration.

Methods

This retrospective study enrolled patients aged ≥18 years who were admitted to the intensive care unit and treated with ≥3 intravenous vancomycin doses during CRRT, and who underwent vancomycin TDM. Demographic and other information were collected. Multivariate logistic regression was used assess the risk factors for exceeding the target concentration.

Results

Sixty-nine patients were included, and 40.6% patients underwent TDM. Additionally, 14.5% of patients reached the optimal concentration, and 87.5% of patients who exceeded the target received a daily dose adjustment. The cumulative dose of vancomycin and serum albumin were risk factors for exceeding the target concentration in patients on CRRT.

Conclusions

Patients on CRRT did not meet the optimal vancomycin management; <50% of the patients routinely received vancomycin TDM, and <15% achieved the optimal concentration. Fewer patients in the subtherapeutic group received a daily dose adjustment than those who exceeded the target concentration. Cumulative vancomycin and serum albumin doses before TDM were the risk factors for exceeding the target concentration in CRRT patients.

Vancomycin dosing in patients with obesity

In an effort to expedite the publication of articles related to the COVID-19 pandemic, AJHP is posting these manuscripts online as soon as possible after acceptance. Accepted manuscripts have been peer-reviewed and copyedited, but are posted online before technical formatting and author proofing. These manuscripts are not the final version of record and will be replaced with the final article (formatted per AJHP style and proofed by the authors) at a later time.

Review and evaluation of vancomycin dosing guidelines for obese individuals

INTRODUCTION

Vancomycin dosing decisions are informed by factors such as body weight and renal function. It is important to understand the impact of obesity on vancomycin pharmacokinetics and how this may influence dosing decisions. Vancomycin dosing guidelines use varied descriptors of body weight and renal function. There is uncertainty whether current dosing guidelines result in attainment of therapeutic targets in obese individuals.

AREAS COVERED

Literature was explored using PubMed, Embase and Google Scholar for articles from January 1980 to July 2021 regarding obesity-driven physiological changes, their influence on vancomycin pharmacokinetics and body size descriptors and renal function calculations in vancomycin dosing. Pharmacokinetic simulations reflective of international vancomycin dosing guidelines were conducted to evaluate the ability of using total, ideal and adjusted body weight, as well as Cockcroft-Gault and CKD-EPI equations to attain an area-under-the-curve to minimum inhibitory concentration ratio (AUC₂₄/MIC) target (400-650) in obese individuals.

EXPERT OPINION

Vancomycin pharmacokinetics in obese individuals remains debated. Guidelines that determine loading doses using total body weight, and maintenance doses adjusted based on renal function and adjusted body weight, may be most appropriate for obese individuals. Use of ideal body weight leads to subtherapeutic vancomycin exposure and underestimation of renal function.

Vancomycin dosing in an obese patient with acute renal failure: A case report and review of literature

BACKGROUND

Vancomycin is the most commonly used drug for methicillin-resistant Staphylococcus aureus. The empirical clinical doses of vancomycin based on non-obese patients may not be optimal for obese ones.

CASE SUMMARY

This study reports a case of vancomycin dosing adjustment in an obese patient (body mass index 78.4 kg/m²) with necrotizing fasciitis of the scrotum and left lower extremity accompanied with acute renal failure. Dosing adjustment was performed based on literature review and factors that influence pharmacokinetic parameters are analyzed. The results of the blood drug concentration monitoring confirmed the successful application of our dosing adjustment strategy in this obese patient. Total body weight is an important consideration for vancomycin administration in obese patients, which affects the volume of distribution and clearance of vancomycin. The alterations of pharmacokinetic parameters dictate that vancomycin should be dose-adjusted when applied to obese patients. At the same time, the pathophysiological status of patients, such as renal function, which also affects the dose adjustment of the patient, should be considered.

CONCLUSION

Monitoring vancomycin blood levels in obese patients is critical to help adjust the dosing regimen to ensure that vancomycin concentrations are within the effective therapeutic range and to reduce the incidence of renal injury.

Clinical Practice Guidelines for Therapeutic Drug Monitoring of Vancomycin in the Framework of Model-Informed Precision Dosing: A Consensus Review by the Japanese Society of Chemotherapy and the Japanese Society of Therapeutic Drug Monitoring

Background: To promote model-informed precision dosing (MIPD) for vancomycin (VCM), we developed statements for therapeutic drug monitoring (TDM). Methods: Ten clinical questions were selected. The committee conducted a systematic review and meta-analysis as well as clinical studies to establish recommendations for area under the concentration-time curve (AUC)-guided dosing. Results: AUC-guided dosing tended to more strongly decrease the risk of acute kidney injury (AKI) than trough-guided dosing, and a lower risk of treatment failure was demonstrated for higher AUC/minimum inhibitory concentration (MIC) ratios (cut-off of 400). Higher AUCs (cut-off of 600 μg·h/mL) significantly increased the risk of AKI. Although Bayesian estimation with two-point measurement was recommended, the trough concentration alone may be used in patients with mild infections in whom VCM was administered with q12h. To increase the concentration on days 1–2, the routine use of a loading dose is required. TDM on day 2 before steady state is reached should be considered to optimize the dose in patients with serious infections and a high risk of AKI. Conclusions: These VCM TDM guidelines provide recommendations based on MIPD to increase treatment response while preventing adverse effects.

Vancomycin therapeutic monitoring by measured trough concentration versus Bayesian-derived area under the curve in critically ill patients with cancer

The updated vancomycin guideline and recent studies suggested that trough concentrations may result in underestimation of the actual area under the curve (AUC), leading to excessive dosing and nephrotoxicity. With limited data available on critically ill cancer patients, this study aimed to compare the two methods in this patient population. This was a 5‐year retrospective study on patients treated with vancomycin in the intensive care unit (ICU) of a comprehensive cancer center. The measured trough concentration was compared to Bayesian‐derived AUC/minimum‐inhibitory‐concentration (MIC), considering MIC as 1. Trough concentrations of 15–20 mg/L and AUC of 400–600 mg h/L were considered the targeted goal. Multivariate analysis was performed to identify factors associated with an AUC below the targeted goal. During the study period, 316 patients were included. The mean age was 54 years ±16 (SD); most patients had solid tumors (75%), and 11% had neutropenia. A targeted goal AUC and trough were recorded in 128 (41%) patients and in 64 (20%) patients, respectively. Of the 128 patients with targeted goal AUC, 31 (24%) had targeted goal trough concentrations and 91 (71%) had trough concentrations below 15 mg/L. Furthermore, among the patients with targeted goal trough concentration (n = 64), 33 (52%) had higher than targeted goal AUC. Augmented renal clearance (ARC), defined as a calculated creatinine‐clearance ≥130 ml/min, was associated with an AUC below the targeted goal. In a cohort of critically ill patients with cancer, over two‐thirds of the patients with a targeted goal Bayesian AUC/MIC had trough concentrations below the targeted goal. ARC was associated with AUC below the targeted goal.

Should Therapeutic Drug Monitoring Based on the Vancomycin Area Under the Concentration-Time Curve Be Standard for Serious Methicillin-Resistant Staphylococcus aureus Infections?-No

In this counterpoint we critically appraise the evidence supporting therapeutic drug monitoring based on the vancomycin 24-hour area under the concentration-time curve (AUC24) for serious methicillin-resistant Staphylococcus aureus infections. We reveal methodologically weaknesses and inconsistencies in the data and suggest that, in the absence of clear and convincing evidence of benefit compared with modestly reducing trough targets, alternative strategies are more likely to result in superior safety and efficacy. These include focusing on fundamental antibiotic stewardship to limit vancomycin exposure overall, achieving earlier and more complete source control, and establishing alternative therapeutic options to vancomycin. Implementation of AUC24-based therapeutic drug monitoring will take resources away from these more promising, alternative solutions.

Dosing Recommendations for Vancomycin in Children and Adolescents with Varying Levels of Obesity and Renal Dysfunction: a Population Pharmacokinetic Study in 1892 Children Aged 1-18 Years

Vancomycin is an effective but potentially nephrotoxic antibiotic commonly used for severe infections. Dosing guidelines for vancomycin in obese children and adolescents with or without renal impairment are currently lacking. This study describes the pharmacokinetics of vancomycin in a large pediatric cohort with varying degrees of obesity and renal function to design practical dosing guidelines for this population. A multi-center retrospective population pharmacokinetic study was conducted using data from patients aged 1−18 years who received >1 dose of vancomycin and had ≥1 vancomycin concentration measured between January 2006 and December 2012. Besides pharmacokinetic data, age, gender, body weight, creatinine clearance (CL_cr, bedside Schwartz equation), ward, race, and neutropenic status were collected. Population pharmacokinetic analysis and simulations were performed using NONMEM7.4. A total of 1892 patients (5524 samples) were included, with total body weight (TBW) ranging 6−188 kg (1344 normal weight, 247 overweight, and 301 obese patients) and CL_cr down to 8.6 mL/min/1.73 m². The two-compartment model, with clearance (CL) significantly increasing with TBW and CL_cr, central and peripheral volume of distribution and inter-compartmental clearance increasing with TBW, performed well for all age, weight, and renal function ranges. A dosing guideline is proposed that integrates body weight and CL_cr resulting in effective and safe exposures across all ages, body weight, and renal functions in the pediatric population. We have characterized the full pharmacokinetic profile of vancomycin in obese children and adolescents aged 1−18 years and propose a practical dosing guideline that integrates both body weight and renal function.

A Canadian perspective on the revised 2020 ASHP-IDSA-PIDS-SIDP guidelines for vancomycin AUC-based therapeutic drug monitoring for serious MRSA infections

BACKGROUND

A revised consensus guideline on therapeutic drug monitoring (TDM) of vancomycin for serious methicillin-resistant Staphylococcus aureus (MRSA) infections was recently published with endorsement of numerous American pharmacy and medical societies. Changing practice from trough TDM to area-under-the-curve-(AUC)-guided dosing was suggested.

METHODS

Recent literature was critically appraised to determine whether AUC TDM is appropriate for Canadian hospital practice.

RESULTS

Previous 2009 vancomycin consensus guidelines recommended trough levels of 15-20 mg/L for serious MRSA infections, based on relatively poor evidence for efficacy or safety. In the past decade, aggressive trough targets have led to unnecessary toxicity. Adoption of a TDM strategy using an alternative parameter (AUC) has been suggested, although the evidence for any outcome benefits is low quality. In addition, implementation would require greater resources at health care institutions in the forms of more frequent serum levels or acquisition of costly Bayesian software programs. Most studies on this subject have been observational and retrospective; therefore, relationships between TDM parameters and outcomes have not been convincingly and consistently demonstrated to be causal in nature. Despite claims to the contrary, based on few in silico experiments, available clinical data suggest correlation of trough levels and AUC is high. TDM with lower target trough levels is a simpler solution to reduce risk of toxicity.

CONCLUSIONS

There are serious concerns with adoption of AUC TDM of vancomycin into routine practice in Canada. Trough-based monitoring with modest reduction in target levels remains the most evidence-informed practice at this time.

AUCs and 123s: a critical appraisal of vancomycin therapeutic drug monitoring in paediatrics

The revised vancomycin guidelines recommend implementing AUC24-based therapeutic drug monitoring (TDM) using Bayesian methods in both adults and paediatrics. The motivation for this change was accumulating evidence showing aggressive dosing to achieve high troughs, as recommended in the first guidelines for adults and extrapolated to paediatrics, is associated with increased nephrotoxicity without improving clinical outcomes. AUC24-based TDM requires substantial resources that may need to be diverted from other valuable interventions. It can therefore be justified only after certain assumptions are shown to be true: (i) there is a clear relationship between vancomycin efficacy and/or toxicity and the proposed therapeutic range; and (ii) maintaining exposure within the target range with AUC24-based TDM improves clinical outcomes and/or decreases toxicity. In this review, we critically appraise the scientific basis for these assumptions. We find studies evaluating the relationship between vancomycin AUC24/MIC and efficacy in adults and children do not offer strong support for the recommended lower limit of the proposed therapeutic range (i.e. AUC24/MIC ≥400). Nephrotoxicity in children increases in a stepwise manner along the vancomycin exposure continuum but it is unclear if one parameter (AUC24 versus trough) is a superior predictor. Overall, evidence in children suggests good-to-excellent correlation between AUC24 and trough. Most importantly, there is no convincing evidence that the method of vancomycin TDM has a causal role in improving efficacy or reducing toxicity. These findings question the need to transition to resource-intensive AUC24-based TDM over retaining trough-based TDM with lower targets to minimize nephrotoxicity in paediatrics.

Do Vancomycin Pharmacokinetics Differ Between Obese and Non-obese Patients? Comparison of a General-Purpose and Four Obesity-Specific Pharmacokinetic Models

Over the past decade, numerous obesity-specific pharmacokinetic (PK) models and dosage regimens have been developed. However, it is unclear whether vancomycin PKs differ between obese and other patients after accounting for weight, age, and kidney function. In this study, the authors investigated whether using obesity-specific population PK models for vancomycin offers any advantage in accuracy and precision over using a recently developed general-purpose model.

Dose recommendations for gentamicin in the real-world obese population with varying body weight and renal (dys)function

Background

The impact of weight on pharmacokinetics of gentamicin was recently elucidated for (morbidly) obese individuals with normal renal function.

Objectives

To characterize the pharmacokinetics of gentamicin in real-world obese patients, ultimately to develop dose recommendations applicable across the entire obese population.

Methods

In two large Dutch hospitals, all admitted patients with BMI ≥25 kg/m² with at least one gentamicin administration, at least one gentamicin and at least one creatinine serum concentration measurement were included. Data from one hospital, obtained from electronic health records, combined with prospective data of non-obese and morbidly obese people with normal renal function, served as the training dataset, and data from the second hospital served as the external validation dataset.

Results

In the training dataset [1187 observations from 542 individuals, total body weight (TBW) 52–221 kg and renal function (CKD-EPI) 5.1–141.7 mL/min/1.73 m²], TBW was identified as a covariate on distribution volume, and de-indexed CKD-EPI and ICU stay on clearance (all P < 0.001). Clearance was 3.53 L/h and decreased by 0.48 L/h with each 10 mL/min reduction in de-indexed CKD-EPI. The results were confirmed in the external validation (321 observations from 208 individuals, TBW 69–180 kg, CKD-EPI 5.3–130.0 mL/min/1.73 m²).

Conclusions

Based on the study, we propose specific mg/kg dose reductions with decreasing CKD-EPI values for the obese population, and extension of the dosing interval beyond 24 h when CKD-EPI drops below 50 mL/min/1.73 m². In ICU patients, a 25% dose reduction could be considered. These guidelines can be used to guide safe and effective dosing of gentamicin across the real-world obese population.

Population Pharmacokinetics of Vancomycin in Kidney Transplant Recipients: Model Building and Parameter Optimization

Background

Depending on the renal function of patients and many other influencing factors, studies on vancomycin pharmacokinetics show significant inter- and intra-individual variability. The present study was conducted using a population pharmacokinetics method to investigate the pharmacokinetic parameters and identified their influencing covariates for intravenous vancomycin in adult kidney transplant recipients.

Methods

The drug monitoring data included 56 adult renal transplant recipients who received intravenous vancomycin as prophylactic medication. The analysis was performed by a population approach with NONMEM. Data were collected mainly during the first week after transplantation. Monitoring of vancomycin trough concentration in blood was initiated mainly 3–5 days after the initial administration.

Results

The one-compartment open model was optimal and adequately described the data. Body weight (WT) and estimated glomerular filtration rate (GFR) were identified as significant covariates of the pharmacokinetic parameters CL and V of intravenous vancomycin in the kidney transplant patients. The typical values of vancomycin CL and V were 2.08 L h^-1 and 63.2 L, respectively. A dosage strategy scheme according to model results was also designed.

Conclusion

Both WT and GFR of the kidney transplant patients positively influence the pharmacokinetic parameters CL and V for intravenous vancomycin. Our population pharmacokinetic model provides a reference for vancomycin dosage adjustment in kidney transplant recipients.

The role of antibiotic pharmacokinetic studies performed post-licensing

Post-licensing pharmacometric studies can provide a better understanding of the pharmacokinetic (PK) alterations in special patient populations and may lead to better clinical outcomes. Some patient populations exhibit markedly different pathophysiology to general ward patients or healthy individuals. This may be developmental (paediatric patients), a manifestation of an underlying disease pathology (patients with obesity or haematological malignancies) or due to medical interventions (critically ill patients receiving extracorporeal therapies). This paper outlines the factors that affect the PK of special patient populations and describes some novel methods of antimicrobial administration that may increase antimicrobial concentrations at the site of infection and improve treatment of severe infection.

Drug Dosing Recommendations for All Patients: A Roadmap for Change

Most drug labels do not contain dosing recommendations for a significant portion of real‐world patients for whom the drug is prescribed. Current label recommendations predominately reflect the population studied in pivotal trials that typically exclude patients who are very young or old, emaciated or morbidly obese, pregnant, or have multiple characteristics likely to influence dosing. As a result, physicians may need to guess the correct dose and regimen for these patients. It is now feasible to provide dose and regimen recommendations for these patients by integrating available scientific knowledge and by utilizing or modifying current regulatory agency‐industry practices. The purpose of this commentary is to explore several factors that should be considered in creating a process that will provide more effective, safe, and timely drug dosing recommendations for most, if not all, patients. These factors include the availability of real‐world data, development of predictive models, experience with the US Food and Drug Administration (FDA)’s pediatric exclusivity program, development of clinical decision software, funding mechanisms like the Prescription Drug Users Fee Act (PDUFA), and harmonization of global regulatory policies. From an examination of these factors, we recommend a relatively simple, efficient expansion of current practices designed to predict, confirm, and continuously improve drug dosing for more patients. We believe implementing these recommendations will benefit patients, payers, industry, and regulatory agencies.

Population pharmacokinetics of vancomycin in obesity: Finding the optimal dose for (morbidly) obese individuals

Aims

For vancomycin treatment in obese patients, there is no consensus on the optimal dose that will lead to the pharmacodynamic target (area under the curve 400–700 mg h L⁻¹). This prospective study quantifies vancomycin pharmacokinetics in morbidly obese and nonobese individuals, in order to guide vancomycin dosing in the obese.

Methods

Morbidly obese individuals (n = 20) undergoing bariatric surgery and nonobese healthy volunteers (n = 8; total body weight [TBW] 60.0–234.6 kg) received a single vancomycin dose (obese: 12.5 mg kg⁻¹, maximum 2500 mg; nonobese: 1000 mg) with plasma concentrations measured over 48 h (11–13 samples per individual). Modelling, internal validation, external validation using previously published data and simulations (n = 10.000 individuals, TBW 60–230 kg) were performed using NONMEM.

Results

In a 3‐compartment model, peripheral volume of distribution and clearance increased with TBW (both p < 0.001), which was confirmed in the external validation. A dose of 35 mg kg⁻¹ day⁻¹ (maximum 5500 mg/day) resulted in a > 90% target attainment (area under the curve > 400 mg h L⁻¹) in individuals up to 200 kg, with corresponding trough concentrations of 5.7–14.6 mg L⁻¹ (twice daily dosing). For continuous infusion, a loading dose of 1500 mg is required for steady state on day 1.

Conclusion

In this prospective, rich sampling pharmacokinetic study, vancomycin clearance was well predicted using TBW. We recommend that in obese individuals without renal impairment, vancomycin should be dosed as 35 mg kg⁻¹ day⁻¹ (maximized at 5500 mg/day). When given over 2 daily doses, trough concentrations of 5.7–14.6 mg L⁻¹ correspond to the target exposure in obese individuals.