Population pharmacokinetic model of cefazolin in total hip arthroplasty

Systemic antibiotic prophylaxis in arthroplasty - a narrative review of how many doses are optimal

Systemic antibiotic prophylaxis (SAP) is well-established in arthroplasty to prevent periprosthetic joint infection. However, the optimal duration and dosing of SAP remain a matter of debate, as evidenced by ongoing discordance between recommendations and clinical practice, reflected in the heterogeneity and imprecision of national and societal guidelines. The evidence currently available regarding the duration of SAP is summarised and discussed, specifically the postoperative repeated administration of antimicrobials within the first 24 h. The evidence available suffers from limitations, specifically deficiencies in outcome assessments in the available randomised controlled trials. Observational studies suggest that a short postoperative prolongation (<24 h) of SAP in arthroplasty may result in superior long-term outcomes compared to a single dose, and that an optimal dosing strategy, which warrants further prospective evaluation, may involve 'stacked dosing' in the early postoperative period, with re-administration every two half-lives when using commonly recommended beta-lactam antibiotics, instead of repetition at usual dosing intervals over 24 h. A stacked approach would also cover recognised indications for repetition, such as major blood loss and increased duration of operation, potentially simplifying prescribing protocols. Pharmacokinetic simulations are provided to illustrate the distinct concentration-time profiles associated with different prophylaxis regimens. Prolonging SAP beyond 24 h is not recommended. This review concludes by providing recommendations for further research, particularly a call to document SAP regimens with sufficient detail (choice of drug, dose regimen, and duration of administration) into established national arthroplasty registries, which should rapidly enable a significantly more nuanced understanding of these critical issues than permitted by the current literature.

Dose optimization of cefazolin in South African children undergoing cardiac surgery with cardiopulmonary bypass

Cefazolin is an antibiotic used to prevent surgical site infections. During cardiac surgery with cardiopulmonary bypass (CPB), its efficacy target could be underachieved. We aimed to develop a population pharmacokinetic model for cefazolin in children and optimize the prophylactic dosing regimen. Children under 25 kg undergoing cardiac surgery with CPB and receiving cefazolin at standard doses (50 mg/kg IV every 4-6 h) were included in this analysis. A population pharmacokinetic model and Monte Carlo simulations were used to evaluate the probability of target attainment (PTA) for efficacy and toxicity with the standard regimen and an alternative regimen of continuous infusion, where loading and maintenance doses were calculated from model-derived individual parameters. Twenty-two patients were included, with median (range) age, body weight, and eGFR of 19.5 (1-94) months, 8.7 (2-21) kg, and 116 (48-159) mL/min, respectively. Six patients received an additional dose in the CPB circuit. A two-compartment disposition model with an additional compartment for the CPB was developed, including weight-based allometric scaling and eGFR. For a 10 kg patient with eGFR of 120 mL/min/1.73 m2, clearance was estimated as 0.856 L/h. Simulations indicated that the standard dosing regimen fell short of achieving the efficacy target >40% of the time within a dosing duration and in patients with good renal function, PTA ranged from <20% to 70% for the smallest to the largest patients, respectively, at high MICs. In contrast, the alternative regimen consistently maintained target concentrations throughout the procedure for all patients while using a lower overall dose.

Heparin Dosing Regimen Optimization in Veno-Arterial Extracorporeal Membrane Oxygenation: A Pharmacokinetic Analysis

BACKGROUND

Unfractionated heparin is administered in patients undergoing veno-arterial extracorporeal membrane oxygenation (VA-ECMO). Anticoagulation monitoring is recommended, with an anti-activated factor X (anti-Xa) targeting 0.3 to 0.7 IU/mL. Owing to heparin's heterogeneous pharmacokinetic properties, anti-Xa is unpredictable, generating a challenge in anticoagulation practices. The aim of this study was to build a pharmacokinetic model of heparin accounting for potential confounders, and derive an optimized dosing regimen for a given anti-Xa target.

METHODS

Adult patients undergoing VA-ECMO were included between January 2020 and June 2021. Anticoagulation was managed with an initial 100 IU/kg heparin loading dose followed by a continuous infusion targeting 0.2 to 0.7 IU/mL anti-Xa. The data were split into model development and model validation cohorts. Statistical analysis was performed using a nonlinear mixed effects modeling population approach. Model-based simulations were performed to develop an optimized dosing regimen targeting the desired anti-Xa.

RESULTS

A total of 74 patients were included, with 1703 anti-Xa observations. A single-compartment model best fitted the data. Interpatient variability for distribution volume was best explained by body weight, C-reactive protein and ECMO indication (post-cardiotomy shock or medical cardiogenic shock), and interpatient variability for elimination clearance was best explained by serum creatinine and C-reactive protein. Simulations using the optimized regimen according to these covariates showed accurate anti-Xa target attainment.

CONCLUSION

In adult patients on VA-ECMO, heparin's effect increased with serum creatinine and medical indication, whereas it decreased with body weight and systemic inflammation. We propose an optimized dosing regimen accounting for key covariates, capable of accurately predicting a given anti-Xa target.

Population pharmacokinetics of antibacterial agents in the older population: a literature review

INTRODUCTION

Older individuals face an elevated risk of developing bacterial infections. The optimal use of antibacterial agents in this population is challenging because of age-related physiological alterations, changes in pharmacokinetics (PK) and pharmacodynamics (PD), and the presence of multiple underlying diseases. Therefore, population pharmacokinetics (PPK) studies are of great importance for optimizing individual treatments and prompt identification of potential risk factors.

AREA COVERED

Our search involved keywords such as 'elderly,' 'old people,' and 'geriatric,' combined with 'population pharmacokinetics' and 'antibacterial agents.' This comprehensive search yielded 11 categories encompassing 28 antibacterial drugs, including vancomycin, ceftriaxone, meropenem, and linezolid. Out of 127 studies identified, 26 (20.5%) were associated with vancomycin, 14 (11%) with meropenem, and 14 (11%) with piperacillin. Other antibacterial agents were administered less frequently.

EXPERT OPINION

PPK studies are invaluable for elucidating the characteristics and relevant factors affecting the PK of antibacterial agents in the older population. Further research is warranted to develop and validate PPK models for antibacterial agents in this vulnerable population.

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.