Population Pharmacokinetic and Pharmacodynamic Target Attainment Analysis of Cefazolin in the Serum and Hip Joint Capsule of Patients Undergoing Total Hip Arthroplasty

Target Attainment and Population Pharmacokinetics of Cefazolin in Patients with Invasive Staphylococcus aureus Infections: A Prospective Cohort Study

This study aimed to determine cefazolin target attainment in patients with invasive Staphylococcus aureus (S. aureus) infections and to develop a population pharmacokinetic (PK) model. Adult patients with invasive S. aureus infections treated with cefazolin bolus infusions were included. Unbound and total trough and mid-dose cefazolin concentrations were measured, and strain-specific MICs were determined. The primary outcome was the proportion of patients attaining 100% fT>MIC at all time points evaluated. A population PK model was developed, using non-linear mixed-effects modelling. Overall, 51 patients were included, with a total of 226 unbound and total cefazolin concentrations measured (mean: 4.4 per patient). The median daily dosage in patients with an estimated glomerular filtration rate of >60 mL/min/m2 was 8 g. The median age was 74 years (interquartile range (IQR) 57-82) and 26% were female. A history of chronic kidney disease and acute kidney injury were present in 10/51 (19.6%) and 6/51 (11.7%), respectively. Achievement of 100% fT>MIC occurred in 86% of the patients and decreased to 45% when a target of 100% fT>4xMIC was evaluated. The mean unbound cefazolin fraction was 27.0% (standard deviation (SD) 13.4). Measured and estimated mean cefazolin trough concentrations differed significantly [13.1 mg/L (SD 23.5) vs. 7.4 mg/L (SD 7.9), p < 0.001]. In the population PK model, elevated estimated creatinine clearance and bolus instead of continuous application were covariates for target non-attainment. In conclusion, cefazolin target achievement was high, and the measurement of the unbound cefazolin concentration may be favored. The Monte Carlo simulations indicated that target attainment was significantly improved with continuous infusion.

Population pharmacokinetics and pharmacodynamic target attainment analysis of cefazolin using total and unbound serum concentration in patients with prostatectomy or nephrectomy

The aim of this study was to analyze the population pharmacokinetics of total and unbound concentrations of prophylactic cefazolin (CFZ) in patients with prostatectomy or nephrectomy. We also aimed to calculate a pharmacodynamics target unbound concentration that exceeded the minimum inhibitory concentration (MIC), to design an effective dosing regimen. Briefly, 614 total concentration and 610 unbound concentration samples from 152 individuals were evaluated, using a nonlinear mixed-effects model. The obtained pharmacodynamics index target value reflected the probability of maintaining CFZ unbound trough concentrations exceeding MIC90, 0.5 mg/L, and MIC50, and 1.0 mg/L, to account for methicillin-susceptible Staphylococcus aureus (MSSA) or Escherichia coli. Population pharmacokinetics were estimated using a two-compartment model with nonlinear protein binding. Unbound systemic clearance (CL) was significantly associated with creatinine clearance, while the maximum protein-binding constant was significantly associated with albumin levels. The probability of achieving an unbound concentration exceeding the MIC50 for E. coli or MIC90 for MSSA in a patient with normal renal function following a 1 g CFZ infusion over 15 min was above 90% at 3 h after the initial dose. Our findings indicated that population pharmacokinetic parameters are useful for determining unbound CFZ pharmacokinetics and evaluating intraoperative CFZ redosing intervals.

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.

Association of serum and fat tissue antibiotic concentrations with surgical site infections in lower gastrointestinal surgery

BACKGROUND

During surgery, the effectiveness of perioperative prophylactic antibiotic administration against surgical site infections is inferred from serum concentrations and not from tissues where local infections occur. This study aimed to measure the serum and tissue concentrations of cefmetazole in colorectal surgery cases to clarify whether there is an association between the incidence of surgical site infections and antibiotic concentrations.

METHODS

This prospective cohort study was performed at a single tertiary care center. The data of 105 patients who underwent colorectal surgery between October 2017 and September 2019 were evaluated. The primary outcome was the incidence of surgical site infections. Univariate analysis was performed to investigate the association between surgical site infections, perioperative factors, and the serum and tissue concentrations of cefmetazole.

RESULTS

The incidence of surgical site infections was 13/105 (12.4%). Cefmetazole concentrations were measured at initial incision (serum; 101 vs 93.1 mg/L, P = .75, subcutaneous fat tissue; 2.8 vs 3.7 mg/g, P = .15), intestinal resection (serum; 35.1 vs 36.7 mg/L, P = .63, mesenteric adipose tissue; 1.3 vs 1.7 mg/g, P = .55), and at skin closure (serum; 34.5 vs 44.8 mg/L, P = .18, subcutaneous fat tissue; 1.0 vs 2.2 mg/g, P = .09). In univariate analysis with P ≤ .10, cefmetazole concentration in subcutaneous fat tissue at skin closure was found to be a significant risk factor for surgical site infections. Age, additional intraoperative administration of cefmetazole, and creatinine clearance were also significant risk factors for the occurrence of surgical site infections.

CONCLUSION

Low subcutaneous fat cefmetazole concentrations at skin closure during gastrointestinal operations may also be involved in the occurrence of surgical site infections.

Population pharmacokinetic model of cefazolin in total hip arthroplasty

Cefazolin is an antibiotic recommended for infection prevention in total hip arthroplasty (THA). However, the dosing regimen necessary to achieve therapeutic concentrations in obese patients remains unclear. The aim of this study was to conduct a population analysis of cefazolin pharmacokinetics (PK) and assess whether cefazolin administration should be weight adapted in THA. Adult patients undergoing THA surgery received an injection of 2000 mg of cefazolin, doubled in the case of BMI > 35 kg/m² and total body weight > 100 kg. A population PK study was conducted to quantify cefazolin exposure over time compared to the therapeutic concentration threshold. A total of 484 cefazolin measurements were acquired in 100 patients, of whom 29% were obese. A 2-compartment model best fitted the data, and creatinine clearance determined interpatient variability in elimination clearance. Our PK simulations using a 2000 mg cefazolin bolus showed that cefazolin concentrations remained above the threshold throughout surgery, regardless of weight or renal function. A 2000 mg cefazolin single injection without adaptation to weight or renal function and without intraoperative reinjection was efficient in maintaining therapeutic concentrations throughout surgery. The optimal target concentration and necessary duration of its maintenance remain unclear.