The pharmacokinetics of antibiotics in patients with obesity: a systematic review and consensus guidelines for dose adjustments

Obesity can cause physiological changes resulting in antibiotic pharmacokinetic alterations and suboptimal drug exposures. This systematic review aimed to summarise the available evidence on this topic and provide guidance for dose adjustment of antibiotics in adult (age ≥18 years) patients with obesity (BMI >30 kg/m2). We searched PubMed, Embase, and CENTRAL databases to find relevant studies published between database inception and Dec 30, 2023. We initially identified 6113 studies, which became 4654 studies after duplicate removal, and 128 studies were included in the final review. β-lactam antibiotics were most commonly studied (57 studies), followed by the group of glycopeptides, lipoglycopeptides, and oxazolidinones (45 studies). The certainty of evidence was low or very low for all antibiotics and a meta-analysis was not possible due to the heterogeneity of study populations and methods. Obesity modestly alters the pharmacokinetics of β-lactam antibiotics, but evidence does not support routine dose adjustments. For aminoglycosides and glycopeptides, the impact of obesity on pharmacokinetics is evident and weight-based dosing is recommended. Data are sparse for other antibiotic classes and research needs are described. In the absence of robust pharmacokinetic data, therapeutic drug monitoring can be used to guide individualised dosing.

Surgical Antibiotic Prophylaxis Dosing in Adult Patients with Obesity: A Comprehensive Review of Pharmacokinetic and Pharmacodynamic Data

Surgical antibiotic prophylaxis is an important measure to prevent postoperative surgical site infections. Current guideline recommendations do not treat obesity specifically, although it can affect pharmacokinetics and pharmacodynamics. The objective of this review was to synthesize current evidence on the need for obesity-related dosing adjustments in surgical antibiotic prophylaxis. MEDLINE and Cochrane Library were searched for studies investigating antibiotic prophylaxis dosing in surgical patients with obesity. Outcomes of interest were pharmacokinetic parameters such as plasma and interstitial fluid concentrations, area under the concentration time curve in plasma and in interstitial fluid, and other pharmacokinetic measures. Thirty studies investigating cefazolin, cefoxitin, cefuroxime, piperacillin/tazobactam, meropenem, ertapenem, metronidazole, vancomycin, ciprofloxacin, and gentamicin were included in this analysis. Except for metronidazole, cefoxitin, and gentamicin, there is currently no evidence suggesting the need for dosing adjustments.

First-time cefuroxime target tissue concentrations in long-lasting spine surgery: Continuous evaluation after repeated weight-dosed administrations

AIMS

Antimicrobial prophylaxis is central in preventing postoperative spine infections, yet knowledge on clinical target spine tissue concentrations remain limited. Current dosing regimens often involve fixed doses based on empirical knowledge, surrogate measures, non-clinical evidence and methodology of variying quality. The objective was to continuously evaluate peri- and postoperative cefuroxime target tissue concentrations in long-lasting spine surgery.

METHODS

Twenty patients scheduled for spine deformity surgery with hypotensive anaesthesia completed the study. Weight-dosed cefuroxime was administered intravenously (20 mg/kg) to all patients preoperativey and after 4 h. Microdialysis probes were placed in vertebral bone (intraoperative sampling), paravertebral muscle, subcutaneous tissue and profoundly/superficially in the wound. Microdialysates and plasma samples were obtained for up to 12 h. The primary endpoint was the time with cefuroxime concentrations above the minimal inhibitory concentration for Staphylococcus aureus of 4 μg/mL as a percentage (%fT>MIC4).

RESULTS

The median cefuroxime %fT>MIC4 (range) of patients' individual surgery time was 100% (100-100) in all investigated tissues and plasma. Median cefuroxime %fT>MIC4 (range) in the first dosing interval was 93% (93-93) in vertebral bone, paravertebral muscle and subcutaneous tissue, and 100% (99-100) in plasma. Median cefuroxime %fT>MIC4 (range) in the second dosing interval was 85% (52-100) in paravertebral muscle, 94% (52-100) in subcutaneous tissue, 99% (71-100) in the profound wound, 100% (72-100) in the superficial wound, and 70% (42-100) in plasma.

CONCLUSIONS

Repeated weight-dosed intravenous cefuroxime administrations (20 mg/kg) provided homogenous and sufficient intraoperative target tissue exposure of cefuroxime (100% fT>MIC4) in long-lasting spine surgery with hypotensive anaesthesia and postoperative exposure (>4 μg/mL) for 5.5-7.5 h.

Evaluation of the need for dosing adaptations in obese patients for surgical antibiotic prophylaxis: a model-based analysis of cefazolin pharmacokinetics

BACKGROUND

Cefazolin is used as a prophylactic antibiotic to reduce surgical site infections (SSIs). Obesity has been identified as a risk factor for SSIs. Cefazolin dosing recommendations and guidelines are currently inconsistent for obese patients. As plasma and target-site exposure might differ, pharmacokinetic data from the sites of SSIs are essential to evaluate treatment efficacy: these data can be obtained via tissue microdialysis. This analysis was designed to evaluate the need for dosing adaptations in obese patients for surgical prophylaxis.

METHODS

Data from 15 obese (BMImedian = 52.6 kg m-2) and 15 age- and sex-matched nonobese patients (BMImedian = 26.0 kg m-2) who received 2 g cefazolin i.v. infusion for infection prophylaxis were included in the analysis. Pharmacokinetic data from plasma and interstitial space fluid (ISF) of adipose tissue were obtained and analysed simultaneously using nonlinear mixed-effects modelling. Dosing regimens were evaluated by calculating the probability of target attainment (PTA) and the cumulative fraction of response (CFR) for plasma and ISF using unbound cefazolin concentration above minimum inhibitory concentration 100% of the time as target (fT>MIC = 100%). Dosing regimens were considered adequate when PTA and CFR were ≥90%.

RESULTS

Evaluation of cefazolin doses of 1 and 2 g with redosing at either 3 or 4 h by PTA and CFR in plasma and ISF found 2 g cefazolin with redosing at 4 h to be the most suitable dosing regimen for both obese and nonobese patients (PTA >90% and CFR >90% for both).

CONCLUSIONS

This model-based analysis, using fT>MIC = 100% as a target, showed that cefazolin dosing adaptations are not required for surgical prophylaxis in obese patients.

[Perioperative antibiotic prophylaxis in obesity]

BACKGROUND

In terms of perioperative infections, arthroplasty for obese patients represents a high-risk procedure. Correct antibiotic prophylaxis is a central pillar of infection prophylaxis. Studies showed increased infection rates if an antibiotic other than cefazolin was administered for prophylaxis. In patients with anamnestic penicillin allergy, an existing allergy is extremely rare, and the presence of cross-allergies to cephalosporins is similarly rare. Consequently, every effort should be made to administer a first- or second generation cephalosporin such as cefazolin.

DOSAGE

Whether the dosage of antibiotic prophylaxis should be adjusted to the body weight remains unclear due to the limited data available: case series showed increased infection rates when cefazolin was underdosed and recommended increasing the dose to 3 g if the body weight exceeds 120 kg. However, no studies with a higher level of evidence exist. Published studies on the effective antibiotic levels in the tissue remain contradictory with regard to possible weight-dependent dose adjustments. Similarly, there is insufficient data on whether local intraoperative antibiotic prophylaxis may be useful in obese patients. By contrast, there is no evidence for a positive benefit of double prophylaxis with two different antibiotics or prolonged postoperative antibiotic prophylaxis in obesity.

CONCLUSION

In summary, the data on antibiotic prophylaxis is generally insufficient, especially when focussing on possible dose adjustments in obesity. The well-timed administration of a cephalosporin such as cefazolin represents the golden standard in orthopedics and trauma surgery. A possible dose adjustment to 3 g for a body weight over 120 kg appears reasonable considering the low costs and the broad therapeutic window and is therefore recommended in the current AWMF S3 guideline.

Incidence of surgical infection in cefazolin 3 g versus 2 g for colorectal surgery in obese patients

OBJECTIVE

To compare the incidence of surgical site infection (SSI) between cefazolin 3 g and 2 g surgical prophylaxis in patients weighing ≥120 kg that undergo elective colorectal surgery.

METHODS

A multicenter, retrospective cohort study was performed utilizing a validated database of elective colorectal surgeries in Michigan acute care hospitals. Adults weighing ≥120 kg who received cefazolin and metronidazole for surgical prophylaxis between 7/2012 and 6/2021 were included. The primary outcome was SSI, which was defined as an infection diagnosed within 30 days following the principal operative procedure. Multivariable logistic regression was used to identify variables associated with SSI; the exposure of interest was cefazolin 3 g surgical prophylaxis.

RESULTS

A total of 581 patients were included; of these, 367 (63.1%) received cefazolin 3 g, while 214 (36.8%) received 2 g. Patients who received cefazolin 3 g had less optimal antibiotic timing (324 [88.3%] vs 200 [93.5%]; P = .043) and a higher receipt of at least 1 of the prophylaxis antibiotics after incision (22 [6%] vs 5 [2.3%]; P = .043). There was no SSI difference between cefazolin 3 g and 2 g cohorts (23 [6.3%] vs 16 [7.5%], P = .574). When accounting for age, smoking status, and surgical duration, cefazolin 3 g was not associated with a reduction in SSI (adjOR, .64; 95%CI, .32-1.29).

CONCLUSIONS

Surgical prophylaxis with cefazolin 3 g, in combination with metronidazole, was not associated with decreased SSI compared to 2 g dosing in obese patients undergoing elective colorectal surgery.

Dynamic distribution of systemically administered antibiotics in orthopeadically relevant target tissues and settings

This review aimed to summarize the current literature on antibiotic distribution in orthopedically relevant tissues and settings where dynamic sampling methods have been used. PubMed and Embase databases were systematically searched. English-published studies between 2004 and 2024 involving systemic antibiotic administration in orthopedically relevant tissues and settings based on dynamic measurements were included. In total, 5385 titles were identified. After title and abstract screening, 97 eligible studies (43 different antibiotic drugs) were included. The studies covered both preclinical (42%) and clinical studies including healthy and infected tissues (21%) and prophylactic and steady-state situations (35%). Microdialysis emerged as the predominant sampling method in 98% of the studies. Most of the presented antibiotics (80%) were only assessed once or twice. Among the most extensively studied antibiotics were cefuroxime (18 studies), linezolid (9 studies) and vancomycin (9 studies). This review presents valuable insights into the microenvironmental distribution of antibiotics in orthopedically relevant target tissues and settings and seeks to provide a basis for improving dosing recommendations and treatment outcomes. However, it is important to acknowledge that our findings are limited to the specific drug, dosing regimens, administration method and target tissue, and are crucially linked to the selected PK/PD target.

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.

Penetration of Antibiotics into Subcutaneous and Intramuscular Interstitial Fluid: A Meta-Analysis of Microdialysis Studies in Adults

BACKGROUND AND OBJECTIVE

The interstitial fluid of tissues is the effect site for antibiotics targeting extracellular pathogens. Microdialysis studies investigating these concentrations in muscle and subcutaneous tissue have reported notable variability in tissue penetration. This study aimed to comprehensively summarise the existing data on interstitial fluid penetration in these tissues and to identify potential factors influencing antibiotic distribution.

METHODS

A literature review was conducted, focusing on subcutaneous and intramuscular microdialysis studies of antibiotics in both adult healthy volunteers and patients. Random-effect meta-analyses were used to aggregate effect size estimates of tissue penetration. The primary parameter of interest was the unbound penetration ratio, which represents the ratio of the area under the concentration-time curve in interstitial fluid relative to the area under the concentration-time curve in plasma, using unbound concentrations.

RESULTS

In total, 52 reports were incorporated into this analysis. The unbound antibiotic exposure in the interstitial fluid of healthy volunteers was, on average, 22% lower than in plasma. The unbound penetration ratio values were higher after multiple dosing but did not significantly differ between muscle and subcutaneous tissue. Unbound penetration ratio values were lower for acids and bases compared with neutral antibiotics. Neither the molecular weight nor the logP of the antibiotics accounted for the variations in the unbound penetration ratio. Obesity was associated with lower interstitial fluid penetration. Conditions such as sepsis, tissue inflammation and tissue ischaemia were not significantly associated with altered interstitial fluid penetration.

CONCLUSIONS

This study highlights the variability and generally lower exposure of unbound antibiotics in the subcutaneous and intramuscular interstitial fluid compared with exposure in plasma. Future research should focus on understanding the therapeutic relevance of these differences and identify key covariates that may influence them.

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.

Morphomics-informed population pharmacokinetic and physiologically-based pharmacokinetic modeling to optimize cefazolin surgical prophylaxis

INTRODUCTION

Cefazolin is the leading antibiotic used to prevent surgical site infections worldwide. Consensus guidelines recommend adjustment of the cefazolin dose above and below 120 kg without regard to body composition. Algorithms exist to repurpose radiologic data into body composition (morphomics) and inform dosing decisions in obesity.

OBJECTIVES

To compare the current standard of body weight to morphomic measurements as covariates of cefazolin pharmacokinetics and aid dose stratification of cefazolin in patients with obesity undergoing colorectal surgery.

METHODS

This prospective study measured cefazolin plasma, fat, and colon tissue concentrations in colorectal surgery patients in order to develop a morphomics-informed population pharmacokinetic (PopPK) model to guide dose adjustments. A physiologically-based pharmacokinetic (PBPK) model was also constructed to inform tissue partitioning in morbidly obese patients (n = 21, body mass index ≥35 kg/m2 with one or more co-morbid conditions).

RESULTS

Morphomics and pharmacokinetic data were available in 58 patients with a median [min, max] weight and age of 95.9 [68.5, 148.8] kg and 55 [25, 79] years, respectively. The plasma-to-subcutaneous fat partition coefficient was predicted to be 0.072 and 0.060 by the PopPK and PBPK models, respectively. The estimated creatinine clearance (eCLcr ) and body depth at the third lumbar vertebra (body depth_L3) were identified as covariates of cefazolin exposure. The probability of maintaining subcutaneous fat concentrations above 2 μg/mL for 100% of a 4-h surgical period was below 90% when eCLcr ≥105 mL/min and body depth_L3 ≥ 300 mm and less sensitive to the rate of infusion between 5 and 60 min.

CONCLUSIONS

Kidney function and morphomics were more informative than body weight as covariates of cefazolin target site exposure. Data from more diverse populations, consensus on target cefazolin exposure, and comparative studies are needed before a change in practice can be implemented.

Effective Antimicrobial Prophylaxis in Surgery: The Relevance and Role of Pharmacokinetics-Pharmacodynamics

Appropriate surgical antimicrobial prophylaxis (SAP) is an important measure in preventing surgical site infections (SSIs). Although antimicrobial pharmacokinetics-pharmacodynamics (PKPD) is integral to optimizing antibiotic dosing for the treatment of infections, there is less research on preventing infections postsurgery. Whereas clinical studies of SAP dose, preincision timing, and redosing are informative, it is difficult to isolate their effect on SSI outcomes. Antimicrobial PKPD aims to explain the complex relationship between antibiotic exposure during surgery and the subsequent development of SSI. It accounts for the many factors that influence the PKs and antibiotic concentrations in patients and considers the susceptibilities of bacteria most likely to contaminate the surgical site. This narrative review examines the relevance and role of PKPD in providing effective SAP. The dose-response relationship i.e., association between lower dose and SSI in cefazolin prophylaxis is discussed. A comprehensive review of the evidence for an antibiotic concentration-response (SSI) relationship in SAP is also presented. Finally, PKPD considerations for improving SAP are explored with a focus on cefazolin prophylaxis in adults and outstanding questions regarding its dose, preincision timing, and redosing during surgery.

Incomplete Data and Potential Risks of Drugs in People with Obesity

PURPOSE OF REVIEW

To provide examples of knowledge gaps in current pharmaceutical treatments for people with obesity and call for changes to regulatory and pharmaceutical clinical research requirements during the drug discovery and development process.

RECENT FINDINGS

Treatment of obesity and its comorbidities often require the use of prescription drugs, many of which have not been fully evaluated in people with obesity. Despite a growing body of research on this topic, the impact of obesity on the pharmacokinetics and pharmacodynamics of drugs is often under-studied by drug sponsors and regulators, and subsequently underappreciated by clinicians and caretakers. There are currently multiple opportunities for pharmaceuticals to include dosing information specifically for patients with obesity in order to ensure safety and efficacy of drugs in this population. Additionally, there are serious gaps between what is known about the effects of obesity on drug disposition and the current use of drugs according to drug prescribing information and clinical practice. There is currently no requirement to test drugs in people with obesity during the drug approval process, even when preliminary data suggests there may be altered kinetics in this population. The lack of information on the safe and effective use of drugs in people with obesity may be contributing to poorer health outcomes in this population.

Model-Informed Approaches to Support Drug Development for Patients With Obesity: A Regulatory Perspective

Obesity, which is defined as having a body mass index of 30 kg/m2 or greater, has been recognized as a serious health problem that increases the risk of many comorbidities (eg, heart disease, stroke, and diabetes) and mortality. The high prevalence of individuals who are classified as obese calls for additional considerations in clinical trial design. Nevertheless, gaining a comprehensive understanding of how obesity affects the pharmacokinetics (PK), pharmacodynamics (PD), and efficacy of drugs proves challenging, primarily as obese patients are seldom selected for enrollment at the early stages of drug development. Over the past decade, model-informed drug development (MIDD) approaches have been increasingly used in drug development programs for obesity and its related diseases as they use and integrate all available sources and knowledge to inform and facilitate clinical drug development. This review summarizes the impact of obesity on PK, PD, and the efficacy of drugs and, more importantly, provides an overview of the use of MIDD approaches in drug development and regulatory decision making for patients with obesity: estimating PK, PD, and efficacy in specific dosing scenarios, optimizing dose regimen, and providing evidence for seeking new indication(s). Recent review cases using MIDD approaches to support dose selection and provide confirmatory evidence for effectiveness for patients with obesity, including pediatric patients, are discussed. These examples demonstrate the promise of MIDD as a valuable tool in supporting clinical trial design during drug development and facilitating regulatory decision-making processes for the benefit of patients with obesity.

Paddle Lead Spinal Cord Stimulation in the Morbidly Obese Patient Population: Outcomes and Complications in a Single-Surgeon Cohort

BACKGROUND

Paddle lead spinal cord stimulation (SCS) is used to treat refractory chronic pain. Morbidly obese patients seek SCS to reduce chronic pain. However, these patients face worse surgical outcomes, and the SCS literature has not evaluated safety and efficacy in this patient population. This study is the largest single-surgeon case series to date on morbidly obese patients with paddle lead SCS implantations. The primary objective is to report postoperative complication rates in morbidly obese patients receiving SCS implants. The secondary objective is to report patient-reported pain scores and Patient-Reported Outcomes Measurement Information System (PROMIS) pain interference and physical function scores in these patients.

METHODS

A retrospective chart review was conducted. The patient charts were reviewed from the day of procedure consent to 6 months postop. Demographic information, pain scores, PROMIS scores, neurological complications, infections, and wound complications were documented.

RESULTS

Sixty-seven patients were included. The mean preoperative BMI was 44.47 ± 4.02 kg/m2. The mean age was 58.9 ± 11.4 years old. There were no neurological complications. 3/67 (4%) developed culture-positive infections. Nine out of sixty-seven (13%) patients developed superficial wound dehiscence without underlying infection. The mean postop PROMIS physical function score was 31.6 ± 6.2 (n = 16) and the mean post-op PROMIS pain interference score was 64.0 ± 6.4 (n = 16). There was a reduction in pain scores, from 7.9 ± 1.7 preop to 5.7 ± 2.5 postop (n = 22, P = 0.004).

CONCLUSIONS

Paddle lead SCS implantation is safe for morbidly obese patients. The only minimal-risk complications present were postoperative infections and wound dehiscence. Surgical care can be modified to further reduce the rates of infection and dehiscence.

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

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

Vancomycin Clearance in Obese Adults is not Predictive of Clearance in Obese Adolescents

BACKGROUND AND OBJECTIVE

Contradictory pharmacokinetic (PK) results have been observed between obese adults and obese adolescents, with absolute clearance (CL) reported to be either unaltered, lower, or higher in obese adolescents compared to obese adults. This study investigates the PK of vancomycin in adolescents and adults who are overweight or obese.

METHODS

Data from 125 overweight and obese adolescents (aged 10-18 years, weight 28.3-188 kg) and 81 overweight and obese adults (aged 29-88 years, weight 66.7-143 kg) were analysed using population PK modelling. In addition to age, sex, renal function estimates, and regular weight descriptors, we evaluated standard weight (WT_standard, defined as weight for length, age, and sex in adolescents and weight for length in adults) and excess weight (WT_excess, defined as total body weight (TBW) minus WT_standard) as covariates in order to distinguish between weight resulting from length versus weight resulting from obesity.

RESULTS

Analyzing adolescents and adults together, vancomycin CL was found to increase with TBW and decrease with increasing age (p < 0.001). A covariate analysis investigating adolescents and adults separately found that vancomycin CL increased with WT_standard in adolescents and adults, albeit with different functions, with adolescents having a higher CL per WT_standard than adults. Moreover, in this separate model, adolescent males had 21% higher CL than adolescent females of the same WT_standard, while in adults, CL decreased with increasing age (p < 0.001).

CONCLUSION

There are apparent differences in vancomycin CL in overweight and obese adults versus overweight and obese adolescents, implying that dosing of vancomycin cannot be directly extrapolated between these populations.

Predictive Performance of Physiologically Based Pharmacokinetic Modelling of Beta-Lactam Antibiotic Concentrations in Adipose, Bone, and Muscle Tissues

Physiologically based pharmacokinetic (PBPK) models consist of compartments representing different tissues. As most models are only verified based on plasma concentrations, it is unclear how reliable associated tissue profiles are. This study aimed to assess the accuracy of PBPK-predicted beta-lactam antibiotic concentrations in different tissues and assess the impact of using effect site concentrations for evaluation of target attainment. Adipose, bone, and muscle concentrations of five beta-lactams (piperacillin, cefazolin, cefuroxime, ceftazidime, and meropenem) in healthy adults were collected from literature and compared with PBPK predictions. Model performance was evaluated with average fold errors (AFEs) and absolute AFEs (AAFEs) between predicted and observed concentrations. In total, 26 studies were included, 14 of which reported total tissue concentrations and 12 unbound interstitial fluid (uISF) concentrations. Concurrent plasma concentrations, used as baseline verification of the models, were fairly accurate (AFE: 1.14, AAFE: 1.50). Predicted total tissue concentrations were less accurate (AFE: 0.68, AAFE: 1.89). A slight trend for underprediction was observed but none of the studies had AFE or AAFE values outside threefold. Similarly, predictions of microdialysis-derived uISF concentrations were less accurate than plasma concentration predictions (AFE: 1.52, AAFE: 2.32). uISF concentrations tended to be overpredicted and two studies had AFEs and AAFEs outside threefold. Pharmacodynamic simulations in our case showed only a limited impact of using uISF concentrations instead of unbound plasma concentrations on target attainment rates. The results of this study illustrate the limitations of current PBPK models to predict tissue concentrations and the associated need for more accurate models. SIGNIFICANCE STATEMENT: Clinical inaccessibility of local effect site concentrations precipitates a need for predictive methods for the estimation of tissue concentrations. This is the first study in which the accuracy of PBPK-predicted tissue concentrations of beta-lactam antibiotics in humans were assessed. Predicted tissue concentrations were found to be less accurate than concurrent predicted plasma concentrations. When using PBPK models to predict tissue concentrations, this potential relative loss of accuracy should be acknowledged when clinical tissue concentrations are unavailable to verify predictions.

Population pharmacokinetics and pharmacodynamics of cefazolin using total and unbound serum concentrations in patients with high body weight

The objective of this study was to evaluate the steady state pharmacokinetics and pharmacodynamics of cefazolin in patients with a high body weight. Cefazolin was administered by 0.5-h infusions to 11 patients with total body weight (TBW) ≥120 kg receiving 3 g q8h, and 12 patients with TBW <120 kg receiving 2 g q8h. Total and unbound serum concentration-time data obtained from serial blood samples were analysed simultaneously by population pharmacokinetic modelling using NONMEM. Probability of target attainment (PTA) was calculated for various dosing regimens through Monte Carlo simulations based on the cumulative percentage of the dosing interval that the unbound concentration exceeds the minimum inhibitory concentration (MIC) value for the pathogen at steady state (fT_MIC) ≥40%, ≥60% and 100%. A two-compartment model with non-linear protein binding and allometric scaling of the central volume of distribution using TBW best characterized both total and unbound concentration-time data. Unbound clearance was significantly associated with creatinine clearance, and maximum protein binding constant was significantly associated with serum albumin concentration and body mass index (P <0.05). Based on unbound concentration-time profiles, all simulated regimens achieved PTA >90% at MIC values ≤2 mg/L using fT_MIC ≥40%, at MIC values ≤1 mg/L using fT_MIC ≥60%, and at MIC values ≤0.5 mg/L using fT_MIC of 100%. At fT_MIC ≥60%, 0.5-h infusion of cefazolin 1 g q8h achieved PTA <90% at MIC values ≥2 mg/L in patients with TBW≥120 kg; however, prolonged-infusion and higher-dose regimens improved PTA to >90%. Overall, cefazolin pharmacokinetics are altered considerably in obese patients. Higher-dose and/or prolonged-infusion cefazolin regimens should be considered in patients with TBW ≥120 kg, particularly those with less-susceptible Gram-negative infections.

Chemotherapy and Anticancer Drugs Adjustment in Obesity: A Narrative Review

BACKGROUND

Obese individuals have higher rates of cancer incidence and cancer- related mortality. The worse chemotherapy outcomes observed in this subset of patients are multifactorial, including the altered physiology in obesity and its impact on pharmacokinetics, the possible increased risk of underdosing, and treatment-related toxicity.

AIMS

The present review aimed to discuss recent data on physiology, providing just an overall perspective and pharmacokinetic alterations in obesity concerning chemotherapy. We also reviewed the controversies of dosing adjustment strategies in adult and pediatric patients, mainly addressing the use of actual total body weight and ideal body weight.

METHODS

This narrative review tried to provide the best evidence to support antineoplastic drug dosing strategies in children, adolescents, and adults.

RESULTS

Cardiovascular, hepatic, and renal alterations of obesity can affect the distribution, metabolism, and clearance of drugs. Anticancer drugs have a narrow therapeutic range, and variations in dosing may result in either toxicity or underdosing. Obese patients are underrepresented in clinical trials that focus on determining recommendations for chemotherapy dosing and administration in clinical practice. After considering associated comorbidities, the guidelines recommend that chemotherapy should be dosed according to body surface area (BSA) calculated with actual total body weight, not an estimate or ideal weight, especially when the intention of therapy is the cure.

CONCLUSION

The actual total body weight dosing appears to be a better approach to dosing anticancer drugs in both adults and children when aiming for curative results, showing no difference in toxicity and no limitation in treatment outcomes compared to adjusted doses.

Effectiveness of postoperative oral administration of cephalexin and metronidazole on surgical site infection among obese women undergoing cesarean section: a randomized, double-blind, placebo-controlled, parallel-group study-phase III

BACKGROUND

Cesarean section (CS) is the most frequently performed surgery in the United States. Compared to vaginal delivery, CS has a higher risk of maternal and neonatal mortality, morbidities, and complications, among which surgical site infection (SSI) is the most common. We aimed at evaluating the effectiveness of postoperative oral administration of cephalexin and metronidazole on SSI among obese women undergoing CS.

METHODS

We conducted a randomized, double-blind clinical trial comparing the prophylactic effect of oral cephalexin and metronidazole vs cephalexin and placebo on SSI following CS among obese women. who had received preoperative prophylactic cephalosporin antibiotics. The study was conducted at the Ommolbanin Hospital, affiliated with Mashhad University of Medical Sciences from April 2019 to February 2020.

RESULT

The participants were randomized into the intervention group (n = 210) and the control group (n = 210). At week-1 follow-up, the outcomes were significantly lower in the intervention group as compared to the control group in terms of fever (9% vs 19%, p = 0.003), abnormal discharge from the incision (serous: 8.6% vs 10.5%, purulent: 2.9% vs 16.7%, p < 0.001), incision separation (1% vs 7.1%, p = 0.001), and cellulitis (4.8% vs 13.3%, p = 0.002). At week-2 follow-up, there were no patients in the intervention group with fever, abnormal discharge from the incision, incision separation, or cellulitis and there was a statistically significant difference for fever, abnormal discharge from the incision, and incision separation between the two groups (p < 0.001, p = 0.001, p = 0.014, respectively).

CONCLUSION

Post-operative administration of cephalexin and metronidazole for 48-h post-cesarean delivery among obese women, in addition to the standard pre-operative prophylaxis, reduced the overall rate of surgical site infection and wound infection symptoms in a 2-week follow-up. Trial registration The study protocol was approved by the Iranian Registry of Clinical Trials (IRCTID: IRCT20200608047685N2) on 2021-03-15.

Carol Davila Central Military Emergency University Hospital, 010825 Bucharest, Romania, Torsin LI, Filimon CR, Tănase NV, Moisă E, Negoiță SI, Clinic of Anaesthesia and Intensive Care Medicine, Dr. Carol Davila Central Military Emergency University Hospital, 010825 Bucharest, Romania, Clinic of Anaesthesia and Intensive Care Medicine, Dr. Carol Davila Central Military Emergency University Hospital, 010825 Bucharest, Romania, Department of Anaesthesia and Intensive Care Medicine, Faculty of Medicine, “Carol Davila” University of Medicine and Pharmacy, 020021 Bucharest, Romania 2 Clinic of Anaesthesia and Intensive Care Medicine, Dr. Carol Davila Central Military Emergency University Hospital, 010825 Bucharest, Romania, "Department of Anaesthesia and Intensive Care Medicine, Faculty of Medicine, “Carol Davila” University of Medicine and Pharmacy, 020021 Bucharest, Romania, 3 Clinic of Anaesthesia and Intensive Care Medicine, Elias Emergency University Hospital, 011461 Bucharest, Romania", Department of Anaesthesia and Intensive Care Medicine, Faculty of Medicine, “Carol Davila” University of Medicine and Pharmacy, 020021 Bucharest, Romania, 3 Clinic of Anaesthesia and Intensive Care Medicine, Elias. Individualized surgical antibiotic prophylaxis – why, when, and how?

"Surgical site infections (SSI) greatly concern clinicians, as they are associated with significant morbidity and mortality, prolonged hospitalization, and costs. Antibiotic prophylaxis plays a pivotal role among the procedures that are usually employed for the prevention of surgical-related infections. This narrative review aims to cover some of the particular situations when the clinician might consider individualizing antibiotic prophylaxis for a patient. With the rising incidence of multi-drug resistant bacteria carriage among not only hospitalized or institutionalized patients but also patients from the community, there might be a tendency to use extended-spectrum antibiotics for longer periods for surgical infection prevention. However, the inappropriate use of antibiotics increases the selection pressure, thus favoring the spreading of resistant bacteria. Moreover, specific patient characteristics or pathologies might need to be considered to customize the type, dose, or length of administration of an antibiotic as surgical prophylaxis. Using prosthetic material or prolonged surgeries with large fluid shifts are other situations when individualized antibiotic prophylaxis might be thought of. Keeping in mind that it is of utmost importance that everyone adheres to the current guidelines for surgical antibiotic prophylaxis, customization of local protocols according to well-thought-out strategies might prove beneficial in SSI prevention."

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.

Tigecycline Soft Tissue Penetration in Obese and Non-obese Surgical Patients Determined by Using In Vivo Microdialysis

Background and Objective

Tigecycline, a broad-spectrum glycylcycline antibiotic, is approved for use at a fixed dose irrespective of body weight. However, its pharmacokinetics may be altered in obesity, which would impact on the antibiotic’s effectiveness. The objective of this study was to investigate the plasma and subcutaneous tissue concentrations of tigecycline in obese patients compared with those in a non-obese control group.

Methods

Fifteen obese patients (one class II and 14 class III) undergoing bariatric surgery and 15 non-obese patients undergoing intra-abdominal surgery (mainly tumour resection) received a single dose of 50 or 100 mg tigecycline as an intravenous short infusion. Tigecycline concentrations were measured up to 8 h after dosing in plasma (total concentration), in ultrafiltrate of plasma (free concentration), and in microdialysate from subcutaneous tissue, respectively.

Results

In obese patients, total peak plasma concentration (1.31 ± 0.50 vs 2.27 ± 1.40 mg/L) and the area under the concentration–time curve from 0 to 8 h (AUC_8h,plasma: 2.15 ± 0.42 vs 2.74 ± 0.73 h⋅mg/L), as normalized to a 100 mg dose, were significantly lower compared with those of non-obese patients. No significant differences were observed regarding the free plasma concentration, as determined by ultrafiltration, or the corresponding AUC_8h (fAUC_8h,plasma). Concentrations in interstitial fluid (ISF) of subcutaneous tissue were lower than the free plasma concentrations in both groups, and they were lower in obese compared to non-obese patients: the AUC_8h in ISF (AUC_8h,ISF) was 0.51 ± 0.22 h⋅mg/L in obese and 0.79 ± 0.23 h⋅mg/L in non-obese patients, resulting in a relative tissue drug exposure (AUC_8h,ISF/fAUC_8h,plasma) of 0.38 ± 0.19 and 0.63 ± 0.24, respectively.

Conclusion

Following a single dose of tigecycline, concentrations in the ISF of subcutaneous adipose tissue are decreased in heavily obese subjects, calling for an increased loading dose.

EU Clinical Trials Registration Number

EudraCT No. 2012-004383-22.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13318-022-00789-2.

Plasma and Interstitial Fluid Pharmacokinetics of Prophylactic Cefazolin in Elective Bariatric Surgery Patients

Guidelines for surgical prophylactic dosing of cefazolin in bariatric surgery vary in terms of recommended dose. This study aimed to describe the plasma and interstitial fluid (ISF) cefazolin pharmacokinetics in patients undergoing bariatric surgery and to determine an optimum dosing regimen. Abdominal subcutaneous ISF concentrations (measured using microdialysis) and plasma samples were collected at regular time points after administration of cefazolin 2 g intravenously. Total and unbound cefazolin concentrations were assayed and then modeled using Pmetrics. Monte Carlo dosing simulations (n = 5,000) were used to define cefazolin dosing regimens able to achieve a fractional target attainment (FTA) of >95% in the ISF suitable for the MIC for Staphylococcus aureus in isolates of ≤2 mg · L-1 and for a surgical duration of 4 h. Fourteen patients were included, with a mean (standard deviation [SD]) bodyweight of 148 (35) kg and body mass index (BMI) of 48 kg · m-2. Cefazolin protein binding ranged from 14 to 36% with variable penetration into ISF of 58% ± 56%. Cefazolin was best described as a four-compartment model including nonlinear protein binding. The mean central volume of distribution in the final model was 18.2 (SD 3.31) L, and the mean clearance was 32.4 (SD 20.2) L · h-1. A standard 2-g dose achieved an FTA of >95% for all patients with BMIs ranging from 36 to 69 kg · m-2. A 2-g prophylactic cefazolin dose achieves appropriate unbound plasma and ISF concentrations in obese and morbidly obese bariatric surgery patients.

Prophylactic Cefazolin Dosing in Obesity-a Systematic Review

Currently, there is no consensus on whether a standard 2-g prophylactic cefazolin dose provides sufficient antimicrobial coverage in obese surgical patients. This systematic review analysed both outcome and pharmacokinetic studies, aiming to determine the appropriate cefazolin dose. A systematic search was conducted using 4 databases. In total, 3 outcome and 15 pharmacokinetic studies met the inclusion criteria. All 3 outcome studies concluded that there is no need for increased dose. Also, 9 pharmacokinetic studies reached this conclusion; however, 6 pharmacokinetic studies recommended that 2-g dose is insufficient to achieve adequate plasma or tissue concentrations. The stronger body of evidence supports that 2-g dose of cefazolin is sufficient for surgery lasting up to 4 h; however, large-scale outcome studies are needed to confirm this evidence.

Ciprofloxacin Pharmacokinetics After Oral and Intravenous Administration in (Morbidly) Obese and Non-obese Individuals: A Prospective Clinical Study

Background and Objective

Ciprofloxacin is a fluoroquinolone used for empirical and targeted therapy of a wide range of infections. Despite the increase in obesity prevalence, only very limited guidance is available on whether the ciprofloxacin dose needs to be adjusted when administered orally or intravenously in (morbidly) obese individuals. Our aim was to evaluate the influence of (morbid) obesity on ciprofloxacin pharmacokinetics after both oral and intravenous administration, to ultimately guide dosing in this population.

Methods

(Morbidly) obese individuals undergoing bariatric surgery received ciprofloxacin either orally (500 mg; n = 10) or intravenously (400 mg; n = 10), while non-obese participants received semi-simultaneous oral dosing of 500 mg followed by intravenous dosing of 400 mg 3 h later (n = 8). All participants underwent rich sampling (11–17 samples) for 12 h after administration. Non-linear mixed-effects modelling and simulations were performed to evaluate ciprofloxacin exposure in plasma. Prior data from the literature were subsequently included in the model to explore exposure in soft tissue in obese and non-obese patients.

Results

Overall, 28 participants with body weights ranging from 57 to 212 kg were recruited. No significant influence of body weight on bioavailability, clearance or volume of distribution was identified (all p > 0.01). Soft tissue concentrations were predicted to be lower in obese individuals despite similar plasma concentrations compared with non-obese individuals.

Conclusion

Based on plasma pharmacokinetics, we found no evidence of the influence of obesity on ciprofloxacin pharmacokinetic parameters; therefore, ciprofloxacin dosages do not need to be increased routinely in obese individuals. In the treatment of infections in tissue where impaired ciprofloxacin penetration is anticipated, higher dosages may be required.

Trial Registration

Registered in the Dutch Trial Registry (NTR6058).

Supplementary Information

The online version contains supplementary material available at 10.1007/s40262-022-01130-5.

Application of a Physiologically Based Pharmacokinetic Model to Predict Cefazolin and Cefuroxime Disposition in Obese Pregnant Women Undergoing Caesarean Section

Intravenous (IV) cefuroxime and cefazolin are used prophylactically in caesarean sections (CS). Currently, there are concerns regarding sub-optimal dosing in obese pregnant women compared to lean pregnant women prior to CS. The current study used a physiologically based pharmacokinetic (PBPK) approach to predict cefazolin and cefuroxime pharmacokinetics in obese pregnant women at the time of CS as well as the duration that these drug concentrations remain above a target concentration (2, 4 or 8 µg/mL or µg/g) in plasma or adipose tissue. Cefazolin and cefuroxime PBPK models were first built using clinical data in lean and in obese non–pregnant populations. Models were then used to predict cefazolin and cefuroxime pharmacokinetics data in lean and obese pregnant populations. Both cefazolin and cefuroxime models sufficiently described their total and free levels in the plasma and in the adipose interstitial fluid (ISF) in non–pregnant and pregnant populations. The obese pregnant cefazolin model predicted adipose exposure adequately at different reference time points and indicated that an IV dose of 2000 mg can maintain unbound plasma and adipose ISF concentration above 8 µg/mL for 3.5 h post dose. Predictions indicated that an IV 1500 mg cefuroxime dose can achieve unbound plasma and unbound ISF cefuroxime concentration of ≥8 µg/mL up to 2 h post dose in obese pregnant women. Re-dosing should be considered if CS was not completed within 2 h post cefuroxime administration for both lean or obese pregnant if cefuroxime concentrations of ≥8 µg/mL is required. A clinical study to measure cefuroxime adipose concentration in pregnant and obese pregnant women is warranted.

A validated LC-MS/MS method for the quantitation of cefazolin in human adipose tissue: Application of EMR-Lipid sorbent as an efficient sample clean-up before mass spectrometric analyses

A novel, simple, rapid, and sensitive high-performance liquid chromatography-tandem mass spectrometry method was developed to determine cefazolin concentrations in human adipose tissue. Sample preparation was performed by protein precipitation followed by using Captiva EMR-Lipid plates. The mobile phase consisted of 5 mM ammonium formate and 0.1% formic acid in water and 0.1% formic acid in ACN, and was pumped through a Synergi Fusion-RP column with a gradient elution program at a flow rate of 0.3 mL/min. The mass spectrometer was operated in a positive ion mode. Cloxacillin was used as an internal standard due to the observed cross-signal contribution between cefazolin and ¹³C₂,¹⁵N-cefazolin. The method was validated according to the FDA and EMA guidelines and passed all the acceptance criteria. The calibration range was 0.05-50 µg/mL in adipose tissue homogenate (0.15-150 µg/g in adipose tissue), precision CV < 4.5%, accuracy within 93.1-100.4%. The carry-over was negligible, recovery of the method was high, and no significant matrix effect was present. Rat subcutaneous adipose tissue was demonstrated to be a suitable surrogate matrix for human adipose tissue. The validated method was successfully applied in a pilot pharmacokinetic study and will further be used in a large cohort of non-obese and obese patients dosed prophylactically with cefazolin before surgeries.

Thickness of the Subcutaneous Fat as a Risk Factor for Surgical Site Infection Following Fragility Hip Fracture Surgery

INTRODUCTION

Surgical site infection (SSI) following fragility hip fracture (FHF) surgery is associated with increased morbidity and mortality.

SIGNIFICANCE

Prediction of patients at risk for SSI is fundamental. We aimed to determine whether subcutaneous radiographic fat measurement (SRM) is associated with increased SSI risk.

METHODS

A retrospective case-control comparison of SRMs at 3 locations around the hip. Patients diagnosed with SSI in the first post-operative year were matched with age, gender, surgical year, Charlsons' co-morbidity index score, and surgical type controls, not diagnosed with SSI, at a 1:2 ratio. Measurements included the distance between (1) the sourcil to skin surface (SS), (2) the tip of the greater trochanter to skin surface (TGTS), and (3) the most prominent lateral aspect of the greater trochanter to skin surface.

RESULTS

1430 patients were operated during the study period, of whom 45 patients presented with a diagnosis of SSI and compared to 90 controls. Infections occurred 27.4 ( ± 24.8) days following surgery. SRM significantly differed between groups, and all were higher in the study group; SS, 86.8 ± 25.5 cm vs 74.2 ± 15.3 cm; TGTS, 59.8 ± 26.3 cm vs 47.0 ± 15.8 cm; and LGTS, 45.4 ± 25.1 cm vs 33.2 ± 15.1 cm (P = .003, .004, and .004, respectively). Intraclass correlation coefficients (intra-rater) were high for all measurements (.999 for all). Intraclass correlation coefficients (inter-rater) for SS, TGTS and LGTS were high, .749 (.663.815), .792 (.719.847) and .817 (.751.866), respectively.

CONCLUSIONS

SRMs were found to be a valid and reproducible tool for predicting high risk of SSI in geriatric patients sustaining FHFs.

LEVEL OF EVIDENCE

III.

Safety and effectiveness of high-dose cefazolin in patients with high body weight: A retrospective cohort study

Background

Cefazolin is a commonly used antibiotic for the treatment of mild to severe infections. Despite the use of higher dose of cefazolin (3 g/dose) for surgical prophylaxis in patients with obesity, there is currently a paucity of data identifying the optimal dose to treat infections in this specific patient population.

Methods

This was a multicenter, retrospective cohort study of patients who received cefazolin at weight-based (up to 9 g/day) or standard doses (up to 6 g/day) for the treatment of bacteremia or skin and soft tissue infection (SSTI). Study groups were stratified by body weight and cefazolin dose received. Primary outcome was the composite of treatment-emergent adverse events (TEAEs) and secondary outcome was treatment failure rate.

Results

A total of 208 patients were included for study analysis. Fifty-nine patients had body weight >120 kg. Of these, 33 received high-dose cefazolin while 26 received standard doses. The remaining 149 patients had body weight of ≤120 kg and received standard doses. The occurrence of TEAEs did not differ across the 3 groups. The study also did not find any difference between the rate of treatment failure between groups.

Conclusions

High-dose cefazolin (9 g/day) for the treatment of bacteremia or SSTIs in patients with high body weight was safe and well tolerated. Larger studies are needed to further explore the benefit of high-dose cefazolin in improving clinical outcomes.

The role of postoperative antibiotic duration on surgical site infection after lumbar surgery

OBJECTIVE

Despite a general consensus regarding the administration of preoperative antibiotics, poorly defined comparison groups and underpowered studies prevent clear guidelines for postoperative antibiotics. Utilizing a data set tailored specifically to spine surgery outcomes, in this clinical study the authors aimed to determine whether there is a role for postoperative antibiotics in the prevention of surgical site infection (SSI).

METHODS

The Michigan Spine Surgery Improvement Collaborative registry was queried for all lumbar operations performed for degenerative spinal pathologies over a 5-year period from 2014 to 2019. Preoperative prophylactic antibiotics were administered for all surgical procedures. The study population was divided into three cohorts: no postoperative antibiotics, postoperative antibiotics ≤ 24 hours, and postoperative antibiotics > 24 hours. This categorization was intended to determine 1) whether postoperative antibiotics are helpful and 2) the appropriate duration of postoperative antibiotics. First, multivariable analysis with generalized estimating equations (GEEs) was used to determine the association between antibiotic duration and all-type SSI with adjusted odds ratios; second, a three-tiered outcome-no SSI, superficial SSI, and deep SSI-was calculated with multivariable multinomial logistical GEE analysis.

RESULTS

Among 37,161 patients, the postoperative antibiotics > 24 hours cohort had more men with older average age, greater body mass index, and greater comorbidity burden. The postoperative antibiotics > 24 hours cohort had a 3% rate of SSI, which was significantly higher than the 2% rate of SSI of the other two cohorts (p = 0.004). On multivariable GEE analysis, neither postoperative antibiotics > 24 hours nor postoperative antibiotics ≤ 24 hours, as compared with no postoperative antibiotics, was associated with a lower rate of all-type postoperative SSIs. On multivariable multinomial logistical GEE analysis, neither postoperative antibiotics ≤ 24 hours nor postoperative antibiotics > 24 hours was associated with rate of superficial SSI, as compared with no antibiotic use at all. The odds of deep SSI decreased by 45% with postoperative antibiotics ≤ 24 hours (p = 0.002) and by 40% with postoperative antibiotics > 24 hours (p = 0.008).

CONCLUSIONS

Although the incidence of all-type SSI was highest in the antibiotics > 24 hours cohort, which also had the highest proportions of risk factors, duration of antibiotics failed to predict all-type SSI. On multinomial subanalysis, administration of postoperative antibiotics for both ≤ 24 hours and > 24 hours was associated with decreased risk of only deep SSI but not superficial SSI. Spine surgeons can safely consider antibiotics for 24 hours, which is equally as effective as long-term administration for prophylaxis against deep SSI.

Predicting Antimicrobial Activity at the Target Site: Pharmacokinetic/Pharmacodynamic Indices versus Time-Kill Approaches

Antibiotic dosing strategies are generally based on systemic drug concentrations. However, drug concentrations at the infection site drive antimicrobial effect, and efficacy predictions and dosing strategies should be based on these concentrations. We set out to review different translational pharmacokinetic-pharmacodynamic (PK/PD) approaches from a target site perspective. The most common approach involves calculating the probability of attaining animal-derived PK/PD index targets, which link PK parameters to antimicrobial susceptibility measures. This approach is time efficient but ignores some aspects of the shape of the PK profile and inter-species differences in drug clearance and distribution, and provides no information on the PD time-course. Time–kill curves, in contrast, depict bacterial response over time. In vitro dynamic time–kill setups allow for the evaluation of bacterial response to clinical PK profiles, but are not representative of the infection site environment. The translational value of in vivo time–kill experiments, conversely, is limited from a PK perspective. Computational PK/PD models, especially when developed using both in vitro and in vivo data and coupled to target site PK models, can bridge translational gaps in both PK and PD. Ultimately, clinical PK and experimental and computational tools should be combined to tailor antibiotic treatment strategies to the site of infection.

Weight-based cefuroxime dosing provides comparable orthopedic target tissue concentrations between weight groups - a microdialysis porcine study

Antibiotic prophylaxis is a key element in prevention of surgical site infections. For the majority of orthopedic procedures, antibiotic administration follows fixed dosing regimens irrespective of weight. However, this may result in insufficient antibiotic target tissue concentrations and higher risk of surgical site infections in obese individuals. The aim of this study was to investigate the effect of weight-based cefuroxime dosing on plasma and target tissue concentrations. Eighteen female pigs were allocated into three groups differentiated by weight: 53-57 kg, 73-77 kg, and 93-97 kg. Microdialysis catheters were placed for continuous sampling in bone, muscle, and subcutaneous tissue during an 8h sampling interval. Blood samples were collected as reference. Cefuroxime was administered intravenously as a bolus according to weight (20 mg/kg). The primary endpoint was the time above the cefuroxime minimal inhibitory concentration for Staphylococcus aureus (T > MIC (4 μg/mL)). Comparable target tissue T > MICs (4 μg/mL) were found between weight groups. Mean T > MIC ranged between 116-137 min for plasma, 118-154 min for bone, 109-146 min for the skeletal muscle, and 117-165 min for subcutaneous tissue across the groups. Weight-based cefuroxime (20 mg/kg) dosing approach provides comparable perioperative plasma and target tissue T > MIC (4 μg/mL) in animals between 50-100 kg body weight, and thus a comparable prophylaxis of surgical site infections.

Association Between Antimicrobial Prophylaxis With Double-Dose Cefuroxime and Surgical Site Infections in Patients Weighing 80 kg or More

IMPORTANCE

Many guidelines recommend a weight-adopted dose increase of cefuroxime for surgical antimicrobial prophylaxis (SAP). However, the evidence that this approach is associated with lower rates of surgical site infection (SSI) is limited.

OBJECTIVE

To assess whether double-dose cefuroxime SAP was associated with a decreased SSI rate in patients weighing at least 80 kg.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study included adult patients (>18 years) weighing at least 80 kg who underwent 9 major surgical procedures with a cefuroxime SAP administration from the Swissnoso SSI surveillance system between January 2015 and December 2019 at 142 Swiss hospitals. The follow-up was 30 days for all surgical procedures and 1 year for implant-related operations.

EXPOSURES

Cefuroxime SAP dose (1.5 vs 3.0 g).

MAIN OUTCOMES AND MEASURES

Overall SSI. A mixed-effects logistic regression adjusted for institutional, epidemiological, and perioperative variables was applied. Results were stratified by weight categories as well as by wound contamination classes.

RESULTS

Of 41 076 eligible patients, 37 640 were included, with 22 625 (60.1%) men and a median (IQR) age of 61.9 (49.9-71.1) years. The outcome SSI was met by 1203 patients (3.2%). Double-dose cefuroxime was administered to 13 246 patients (35.2%) and was not significantly associated with a lower SSI rate (adjusted odds ratio [aOR], 0.89; 95% CI, 0.78-1.02; P = .10). After stratification by weight category, double-dose SAP vs single-dose SAP was associated with lower SSI rates among 16 605 patients weighing at least 80 to less than 90 kg (aOR, 0.76; 95% CI, 0.61-0.97; P = .02) but not in the other weight categories (≥90 to <100 kg, 10 342 patients: aOR, 1.12; 95% CI, 0.87-1.47; P = .37; ≥100 to <120 kg, 8099 patients: aOR, 0.99; 95% CI, 0.76-1.30; P = .96; ≥120 kg, 2594 patients: aOR, 0.65; 95% CI, 0.42-1.04; P = .06). After stratification by contamination class, double-dose SAP was associated with lower SSI rates among 1946 patients with contaminated wounds (aOR, 0.49; 95% CI, 0.30-0.84; P = .008) but not those with clean wounds (25 680 patients; aOR, 0.92; 95% CI, 0.76-1.12; P = .44) or clean-contaminated wounds (10 014 patients; aOR, 0.90; 95% CI, 0.73-1.12; P = .37) compared with a single dose.

CONCLUSIONS AND RELEVANCE

In this study, double-dose SAP with cefuroxime for patients weighing at least 80 kg was not consistently associated with a lower SSI rate.

Clinical Outcome and Antibiotic Dosing Differences by Weight in Children With Acute Osteomyelitis

OBJECTIVES

To evaluate for weight-based differences in clinical outcomes and antibiotic dosing variability for children hospitalized with acute hematogenous osteomyelitis (AHO).

METHODS

We performed a retrospective cohort study of children aged 2 to 17 years and hospitalized with a primary AHO International Classification of Diseases, Ninth Revision or International Classification of Diseases, 10th Revision diagnosis code between 2010 and 2017 using the Cerner Health Facts database. Weight categories (healthy, overweight, obesity) were determined by using Centers for Disease Control and Prevention age- and sex-specific BMI percentiles. Rates of procedures, complications, and length of stay (LOS) were compared between groups. Dosing variability between groups was assessed by comparing the initial milligrams per kilogram per day of prescribed antibiotics.

RESULTS

We identified 755 children with AHO for inclusion. Children with overweight and obesity were more likely to undergo surgical procedures (19% and 17%, respectively) compared with children with a healthy weight (10%; P = .009). They also had a longer LOS (5.7 and 5.8 days) than children with a healthy weight (4.9 days; P = .03). There were no differences in complication rates between weight categories. Mean weight-adjusted daily dose for the most frequently prescribed antibiotics was different by weight category, with children in higher weight categories more likely to receive lower weight-based doses.

CONCLUSIONS

Children with overweight and obesity hospitalized for AHO were more likely to undergo procedures, have longer LOS, and receive lower weight-based antibiotic dosing compared with children with a healthy weight. Our findings suggest that weight should be carefully considered when treating children with AHO.

Impact of Changes in Free Concentrations and Drug-Protein Binding on Drug Dosing Regimens in Special Populations and Disease States

Over the last few decades, scientists and clinicians have often focused their attention on the unbound fraction of drugs as an indicator of efficacy and the eventual outcome of drug treatments for specific illnesses. Typically, the total drug concentration (bound and unbound) in plasma is used in clinical trials to assess a compound's efficacy. However, the free concentration of a drug tends to be more closely related to its activity and interaction with the body. Thus far, measuring the unbound concentration has been a challenge. Several mechanistic models have attempted to solve this problem by estimating the free drug fraction from available data such as total drug and binding protein concentrations. The aims of this review are first, to give an overview of the methods that have been used to date to calculate the unbound drug fraction. Second, to assess the pharmacokinetic parameters affected by changes in drug protein binding in special populations such as pediatrics, the elderly, pregnancy, and obesity. Third, to review alterations in drug protein binding in some selected disease states and how these changes impact the clinical outcomes for the patients; the disease states include critical illnesses, transplantation, renal failure, chronic kidney disease, and epilepsy. And finally, to discuss how various disease states shift the ratio of unbound to total drug and the consequences of such shifts on dosing adjustments and reaching the therapeutic target.

Multidirectional facets of obesity management in the metabolic syndrome population after liver transplantation

The obesity pandemic has resulted in an increasing demand for liver transplantation and has significantly altered the profile of liver transplant candidates in addition to affecting posttransplantation outcomes. In this review, we discuss a broad range of clinical approaches that warrant attention to provide comprehensive and patient‐centred medical care to liver transplant recipients, and to be prepared to confront the rapidly changing clinical challenges and ensuing dilemmas. Adipose tissue is a complex and metabolically active organ. Visceral fat deposition is a key predictor of overall obesity‐related morbidity and mortality. Limited pharmacological options are available for the treatment of obesity in the liver transplant population. Bariatric surgery may be an alternative in eligible patients. The rapidly increasing prevalence of nonalcoholic fatty liver disease (NAFLD) is a global concern; NAFLD affects both pre‐ and posttransplantation outcomes. Numerous studies have investigated pharmacological and nonpharmacological management of NAFLD and some of these have shown promising results. Liver transplant recipients are constantly exposed to numerous factors that result in intestinal microbiota alterations, which were linked to the development of obesity, diabetes type 2, metabolic syndrome (MS), NAFLD, and hepatocellular cancer. Microbiota modifications with probiotics and prebiotics bring gratifying results in the management of metabolic complications. Fecal microbiota transplantation (FMT) is successfully performed in many medical indications. However, the safety and efficacy profiles of FMT in immunocompromised patients remain unclear. Obesity together with immunosuppressive treatment, may affect the pharmacokinetic and/or pharmacodynamic properties of coadministered medications. Individualized immunosuppressive regimens are recommended following liver transplantation to address possible metabolic concerns. Effective and comprehensive management of metabolic complications is shown to yield multiple beneficial results in the liver transplant population and may bring gratifying results in improving long‐term survival rates.

Effect of Obesity on Clinical Failure of Patients Treated With β-Lactams

Background

Altered pharmacokinetics in obese patients raise concerns over worse clinical outcomes. This study assessed whether obese patients receiving a β-lactam have worse clinical outcomes compared to nonobese patients and to identify if therapeutic drug monitoring may be beneficial.

Methods

This multicenter, retrospective cohort included hospitalized adults admitted from July 2015 to July 2017 treated with a β-lactam as definitive monotherapy against a gram-negative bacilli for ≥72 hours. Patients were excluded if there was lack of source control or if polymicrobial infections required >1 antibiotic for definitive therapy. Patients were classified based on body mass index (BMI): nonobese (BMI ≤29.9 kg/m²) and obese (BMI ≥30.0 kg/m²). The primary outcome was clinical treatment failure, and secondary outcomes were hospital length of stay, inpatient all-cause mortality, and 30-day all-cause readmission.

Results

There were 257 (43.6%) obese patients and 332 (56.4%) nonobese patients included. The most common infections were urinary (50.9%) and respiratory (31.4%). Definitive treatment was driven by third-generation cephalosporins (46.9%) and cefepime (44.7%). Treatment failure occurred in 131 (51%) obese patients and 109 (32.8%) nonobese patients (P < .001). Obesity and respiratory source were independently associated with increased likelihood of treatment failure. Obese patients were hospitalized longer than nonobese patients (P = .002), but no differences were found for all-cause mortality (P = .117) or infection-related readmission (0 = 0.112).

Conclusions

Obese patients treated with β-lactams have higher rates of treatment failure and longer hospitalization periods than nonobese patients. Future studies are needed to assess the impact of therapeutic drug monitoring and specific dosing recommendations for targeted infection types.

Perioperative administration of cefazolin and metronidazole in obese and non-obese patients: a pharmacokinetic study in plasma and interstitial fluid

OBJECTIVES

To assess plasma and tissue pharmacokinetics of cefazolin and metronidazole in obese patients undergoing bariatric surgery and non-obese patients undergoing intra-abdominal surgery.

PATIENTS AND METHODS

Fifteen obese and 15 non-obese patients received an IV short infusion of 2 g cefazolin and 0.5 g metronidazole for perioperative prophylaxis. Plasma and microdialysate from subcutaneous tissue were sampled until 8 h after dosing. Drug concentrations were determined by HPLC-UV. Pharmacokinetic parameters were calculated non-compartmentally.

RESULTS

In obese patients (BMI 39.5-69.3 kg/m2) compared with non-obese patients (BMI 18.7-29.8 kg/m2), mean Cmax of total cefazolin in plasma was lower (115 versus 174 mg/L) and Vss was higher (19.4 versus 14.2 L). The mean differences in t½ (2.7 versus 2.4 h), CL (5.14 versus 4.63 L/h) and AUC∞ (402 versus 450 mg·h/L) were not significant. The influence of obesity on the pharmacokinetics of metronidazole was similar (Cmax 8.99 versus 14.7 mg/L, Vss 73.9 versus 51.8 L, t½ 11.9 versus 9.1 h, CL 4.62 versus 4.13 L/h, AUC∞ 116 versus 127 mg·h/L). Regarding interstitial fluid (ISF), mean concentrations of cefazolin remained >4 mg/L until 6 h in both groups, and those of metronidazole up to 8 h in the non-obese group. In obese patients, the mean ISF concentrations of metronidazole were between 3 and 3.5 mg/L throughout the measuring interval.

CONCLUSIONS

During the time of surgery, cefazolin concentrations in plasma and ISF of subcutaneous tissue were lower in obese patients, but not clinically relevant. Regarding metronidazole, the respective differences were higher, and may influence dosing of metronidazole for perioperative prophylaxis in obese patients.

Deep surgical site infections following double-dose perioperative antibiotic prophylaxis in adult obese orthopedic patients

BACKGROUND

Obesity is a risk factor for surgical site infections (SSI). Based on retrospective comparisons and pharmacology, many orthopedic centers have adopted weight- or body mass index (BMI)-related antibiotic prophylaxis.

METHODS

Double-dose prophylaxis was introduced in March 2017 for patients weighting >80 kg. The period April 2014 to March 2017 ('before') was compared to the period March 2017 to June 2019 ('after') regarding the impact on deep SSIs.

RESULTS

A total of 9318 surgeries 'before' were compared to 7455 interventions 'after' the introduction of double-dose prophylaxis. Baseline demographic characteristics (age, sex, BMI, American Society of Anesthesiologists score, and duration of surgery) were similar. In the period 'after', 3088 cases (3088/16 773; 18%) received double-dose prophylaxis. Overall, 82 deep SSIs were observed (0.5%). The pathogens were resistant to the standard cefuroxime prophylaxis in 30 cases (30/82; 37%). Excluding these prophylaxis-resistant cases and all of the five hematogenous SSIs, the remaining 47 SSIs (57%) could have been prevented by the preceding prophylaxis. Double-dosing of parenteral cefuroxime from 1.5 g to 3.0 g in obese patients did not reduce deep SSIs (hazard ratio 0.7, 95% confidence interval 0.3-1.6). In the direct group comparison among obese patients >80 kg, the double-dose prophylaxis equally failed to alter the SSI risk (3088/16 726 non-infections vs 8/47 SSI despite double-dose prophylaxis; Chi-square test, P = 0.78).

CONCLUSIONS

In this single-center before-and-after study with almost 17 000 orthopedic surgeries in adult patients, systemic doubling of the perioperative antibiotic prophylaxis in obese patients clinically failed to reduce the overall deep SSI risk.

Pharmacodynamic Evaluation of a Single Dose versus a 24-Hour Course of Multiple Doses of Cefazolin for Surgical Prophylaxis

The optimal perioperative duration for the administration of cefazolin and other prophylactic antibiotics remains unclear. This study aimed to describe the pharmacodynamics of cefazolin for a single 2 g dose versus a 24 h course of a 2 g single dose plus a 1 g eight-hourly regimen against methicillin-susceptible Staphylococcus aureus. Static concentration time-kill assay and a dynamic in vitro hollow-fibre infection model simulating humanised plasma and interstitial fluid exposures of cefazolin were used to characterise the pharmacodynamics of prophylactic cefazolin regimens against methicillin-sensitive Staphylococcus aureus clinical isolates. The initial inoculum was 1 × 105 CFU/mL to mimic a high skin flora inoculum. The static time-kill study showed that increasing the cefazolin concentration above 1 mg/L (the MIC) did not increase the rate or the extent of bacterial killing. In the dynamic hollow-fibre model, both dosing regimens achieved similar bacterial killing (~3-log CFU/mL within 24 h). A single 2 g dose may be adequate when low bacterial burdens (~104 CFU/mL) are anticipated in an immunocompetent patient with normal pharmacokinetics.

Oral drug dosing following bariatric surgery: General concepts and specific dosing advice

Bariatric or weight‐loss surgery is a popular option for weight reduction. Depending on the surgical procedure, gastric changes like decreased transit time and volume and increased pH, decreased absorption surface in the small intestine, decreased exposure to bile acids and enterohepatic circulation, and decreased gastrointestinal transit time may be expected. In the years after bariatric surgery, patients will also substantially lose weight. As a result of these changes, the absorption, distribution, metabolism and/or elimination of drugs may be altered. The purpose of this article is to report the general influence of bariatric surgery on oral drug absorption, and to provide guidance for dosing of commonly used drugs in this special population. Upon oral drug administration, the time to maximum concentration is often earlier and this concentration may be higher with less consistent effects on trough concentrations and exposure. Additionally, prescription of liquid formulations to bariatric patients is supported by some reports, even though the high sugar load of these suspensions may be of concern. Studies on extended‐release medications result in an unaltered exposure for a substantial number of drugs. Also, studies evaluating the influence of timing after surgery show dynamic absorption profiles. Although for this group specific advice can be proposed for many drugs, we conclude that there is insufficient evidence for general advice for oral drug therapy after bariatric surgery, implying that a risk assessment on a case‐by‐case basis is required for each drug.

Which Analysis Approach Is Adequate to Leverage Clinical Microdialysis Data? A Quantitative Comparison to Investigate Exposure and Reponse Exemplified by Levofloxacin

Purpose

Systematic comparison of analysis methods of clinical microdialysis data for impact on target-site drug exposure and response.

Methods

39 individuals received a 500 mg levofloxacin short-term infusion followed by 24-h dense sampling in plasma and microdialysate collection in interstitial space fluid (ISF). ISF concentrations were leveraged using non-compartmental (NCA) and compartmental analysis (CA) via (ii) relative recovery correction at midpoint of the collection interval (midpoint-NCA, midpoint-CA) and (ii) dialysate-based integrals of time (integral-CA). Exposure and adequacy of community-acquired pneumonia (CAP) therapy via pharmacokinetic/pharmacodynamic target-attainment (PTA) analysis were compared between approaches.

Results

Individual AUC_ISF estimates strongly varied for midpoint-NCA and midpoint-CA (≥52.3%CV) versus integral-CA (≤32.9%CV) owing to separation of variability in PK parameters (midpoint-CA = 46.5%–143%CV_PK, integral-CA = 26.4%–72.6%CV_PK) from recovery-related variability only in integral-CA (41.0%–50.3%CV_recovery). This also led to increased variability of AUC_plasma for midpoint-CA (56.0%CV) versus midpoint-NCA and integral-CA (≤33.0%CV), and inaccuracy of predictive model performance of midpoint-CA in plasma (visual predictive check). PTA analysis translated into 33% of evaluated patient cases being at risk of incorrectly rejecting recommended dosing regimens at CAP-related epidemiological cut-off values.

Conclusions

Integral-CA proved most appropriate to characterise clinical pharmacokinetics- and microdialysis-related variability. Employing this knowledge will improve the understanding of drug target-site PK for therapeutic decision-making.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11095-021-02994-1.

Impact of body weight on hemoglobin increments in adult red blood cell transfusion

BACKGROUND

Though weight is a major consideration when transfusing blood in pediatric patients, it is generally not considered when dosing transfusions in adults. We hypothesized that the change in hemoglobin (Hb) concentration is inversely proportional to body weight when transfusing red blood cells (RBC) in adults.

METHODS

A total of 13,620 adult surgical patients at our institution were assessed in this retrospective cohort study (2009-2016). Patients were stratified based on total body weight (kg): 40-59.9 (16.6%), 60-79.9 (40.4%), 80-99.9 (28.8%), 100-119.9 (11.3%), and 120-139.9 (2.9%). The primary outcome was the change in Hb per RBC unit transfused. Subgroup analyses were performed after stratification by sex (male/female) and the total number of RBC units received (1/2/≥3 units). Multivariable models were used to assess the association between weight and change in Hb.

RESULTS

As patients' body weight increased, there was a decrease in the mean change in Hb per RBC unit transfused (40-59.9 kg: 0.85 g/dL, 60-79.9 kg: 0.73 g/dL, 80-99.9 kg: 0.66 g/dL, 100-119.9 kg: 0.60 g/dL, 120-139.9 kg: 0.55 g/dL; p < .0001). This corresponded with a 35% difference in the change in Hb between the lowest and highest weight categories on univariate analysis. Similar trends were seen after subgroup stratification. On multivariable analysis, for every 20 kg increase in patient weight, there was a ~6.5% decrease in the change in Hb per RBC unit transfused (p < .0001).

CONCLUSIONS

Patient body weight differentially impacts the change in Hb after RBC transfusion. These findings justify incorporating body weight into the clinical decision-making process when transfusing blood in adult surgical patients.

Wound infection following implant removal of foot, ankle, lower leg or patella; a protocol for a multicenter randomized controlled trial investigating the (cost-)effectiveness of 2 g of prophylactic cefazolin compared to placebo (WIFI-2 trial)

Background

Elective implant removal (IR) after fracture fixation is one of the most common procedures within (orthopedic) trauma surgery. The rate of surgical site infections (SSIs) in this procedure is quite high, especially below the level of the knee. Antibiotic prophylaxis is not routinely prescribed, even though it has proved to lower SSI rates in other (orthopedic) trauma surgical procedures. The primary objective is to study the effectiveness of a single intravenous dose of 2 g of cefazolin on SSIs after IR following fixation of foot, ankle and/or lower leg fractures.

Methods

This is a multicenter, double-blind placebo controlled trial with a superiority design, including adult patients undergoing elective implant removal after fixation of a fracture of foot, ankle, lower leg or patella. Exclusion criteria are: an active infection, current antibiotic treatment, or a medical condition contraindicating prophylaxis with cefazolin including allergy. Patients are randomized to receive a single preoperative intravenous dose of either 2 g of cefazolin or a placebo (NaCl). The primary analysis will be an intention-to-treat comparison of the proportion of patients with a SSI at 90 days after IR in both groups.

Discussion

If 2 g of prophylactic cefazolin proves to be both effective and cost-effective in preventing SSI, this would have implications for current guidelines. Combined with the high infection rate of IR which previous studies have shown, it would be sufficiently substantiated for guidelines to suggest protocolled use of prophylactic antibiotics in IR of foot, ankle, lower leg or patella.

Trial registration Nederlands Trial Register (NTR): NL8284, registered on 9th of January 2020, https://www.trialregister.nl/trial/8284

The Obese Patient: Facts, Fables, and Best Practices

The prevalence of obesity continues to rise worldwide, and anesthesiologists must be aware of current best practices in the perioperative management of the patient with obesity. Obesity alters anatomy and physiology, which complicates the evaluation and management of obese patients in the perioperative setting. Gastric point-of-care ultrasound (PoCUS) is a noninvasive tool that can be used to assess aspiration risk in the obese patient by evaluating the quantity and quality of gastric contents. An important perioperative goal is adequate end-organ perfusion. Standard noninvasive blood pressure (NIBP) is our best available routine surrogate measurement, but is vulnerable to greater inaccuracy in patients with obesity compared to the nonobese population. Current NIBP methodologies are discussed. Obese patients are at risk for wound and surgical site infections, but few studies conclusively guide the exact dosing of intraoperative prophylactic antibiotics for them. We review evidence for low-molecular-weight heparins and weight-based versus nonweight-based administration of vasoactive medications. Finally, intubation and extubation of the patient with obesity can be complicated, and evidence-based strategies are discussed to mitigate danger during intubation and extubation.