Multicentre, double-blind, randomised controlled clinical trial comparing intermittent cefoxitin administration versus loading bolus followed by continuous infusion for the prevention of surgical site infection in colorectal surgery: the PROPHYLOXITIN study protocol

INTRODUCTION

Surgical site infections (SSIs) are the second leading cause of healthcare-associated infections in Europe with the highest rates being reported in colorectal surgery (ranging from 9% to 30%). Surgical antibiotic prophylaxis (SAP) is one of the most efficient measures for SSI prevention and should be started before surgical incision. Cefoxitin is an antibiotic widely used as SAP for colorectal surgery, but its continuous administration is currently the subject of debate due to its potential pharmacokinetic advantages. Therefore, the aim of the PROPHYLOXITIN study is to demonstrate that a loading dose followed by continuous infusion of cefoxitin during colorectal surgery (intervention group) decreases the rate of SSI compared to an intermittent bolus administration (control group).

METHODS AND ANALYSIS

The PROPHYLOXITIN study is a superiority, prospective, double-blind, randomised and multicentre study of 2000 patients undergoing colorectal surgery. The primary objective is to demonstrate the superiority of a loading dose of cefoxitin followed by continuous infusion over intermittent bolus administration in reducing the proportion of SSIs within 30 days after colorectal surgery. Subjects will be randomised 1:1 using a secure web-based random-number generator to one of two study groups. Randomised allocation of treatment will be done by minimisation and stratified according to the centre, the localisation of surgery (colon or rectum) and the type of surgical procedure (laparoscopy or laparotomy).

ETHICS AND DISSEMINATION

This research has been approved by an independent ethics committee and will be carried out according to the principles of the Declaration of Helsinki and the Good Clinical Practice guidelines. The results of this study will be disseminated through presentation at scientific conferences and publication in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

EudraCT 2022-003262-20 and Clinical trial NCT05755789.

A single-centre randomised controlled trial comparing the standard method and target-controlled infusion as a method of administering cefoxitin, which is used to prevent surgical site infections in colorectal surgical patients: study protocol

BACKGROUND

Prophylactic parenteral administration of antibiotics is strongly recommended to prevent surgical site infection (SSI). Cefoxitin is mainly administered intravenously in colorectal surgery. The current standard method for administering prophylactic antibiotics in adults is to administer a fixed dose quickly before skin incision. The percentage of time that the unbound concentration is maintained above the minimum inhibitory concentration (fT > MIC) during surgery is used as a surrogate measure for the effectiveness of prophylactic antibiotics. Target-controlled infusion (TCI) is a method of administration that changes the infusion rate to maintain a constant target concentration set by the user in consideration of the patient's physical characteristics. When cefoxitin is administered using the TCI method, it is possible that fT > MIC can be well maintained while reflecting the patient's physical characteristics compared to the standard method.

METHODS

This prospective, single-centre, parallel-arm, single-blinded, randomised controlled trial with a 1:1 allocation was designed to compare the effectiveness of the TCI method with that of the standard cefoxitin administration method. We shall enrol 2494 patients scheduled to undergo colon or rectal surgery. Prior to the procedure, we shall randomise each patient to the control group (standard administration method) or study group (TCI method). In the control group, 2 g of cefoxitin was dissolved in 100 ml of normal saline and administered for approximately 10 min. Redosing was performed every 2 h from the start of the first dose of cefoxitin. In the study group, 2 g of cefoxitin was dissolved in 50 ml of normal saline and administered using a commercialised TCI syringe pump until the end of surgery. It was administered at a target concentration of 80 μg/ml using the total concentration pharmacokinetic model of cefoxitin. In all groups, 2 g of cefoxitin was administered using the standard administration method 12 h after the end of surgery. The primary outcome will be the incidence of SSI. The secondary outcome will be the administered dose of cefoxitin. Preoperative, intraoperative, and postoperative data were collected.

DISCUSSION

This study will provide evidence for the effectiveness of administering cefoxitin using the TCI method compared to the standard method.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT05253339 , Registered on February 23, 2022 {2a, 2b}.

Continuous infusion of piperacillin/tazobactam optimizes intraoperative antibiotic exposure in patients undergoing elective pelvic exenteration surgery

Patients undergoing elective pelvic exenteration surgery who receive piperacillin/tazobactam as surgical prophylaxis are at risk of suboptimal intraoperative antibiotic exposure. With this work, we aimed to study the plasma pharmacokinetics of piperacillin and tazobactam in this population to provide dosing recommendations that optimize antibiotic exposure. We developed a prospective, observational, pharmacokinetic study of piperacillin/tazobactam in patients undergoing pelvic exenteration. Population pharmacokinetic analysis and Monte Carlo simulations were performed with Monolix and Simulx software. Probabilities of target attainment of different dosing regimens against the minimum inhibitory concentration (MIC) breakpoints (8 and 16 mg/L) were calculated. Twelve patients were included in the study, with a median age of 50.0 years [interquartile interval (45.3-57.5)] and a median weight of 79.0 kg (61.3-88.3). Median surgical time was 10.5 h (9.8-11.7). A two-compartment linear model best fitted piperacillin and tazobactam data (190 plasma samples). Monte Carlo simulations showed that a lower dose of 2 g/0.25 g loading dose followed by 4 g/0.5 g q8h by continuous infusion provided ≥90% probability of target attainment for MIC = 16 mg/L for most of the patients. For non-continuous infusion regimens, only the 2-hourly bolus re-dosing achieved intraoperative concentrations of piperacillin ≥16 mg/L. Patients with weights ≥ 100 kg and glomerular filtration rates ≥ 120 mL/min required 4 g/0.5 g q6h by continuous infusion after a loading dose. In conclusion, continuous infusion of lower doses of piperacillin/tazobactam is as adequate as the 2-hourly re-dosing recommended by the current guidelines for surgical prophylaxis in pelvic exenteration. Patients with higher weights and glomerular filtration rates are at greater risk of inadequate exposure.

Population pharmacokinetics of prophylactic cefoxitin in elective bariatric surgery patients: a prospective monocentric study

BACKGROUND

This study describes the population pharmacokinetics of cefoxitin in obese patients undergoing elective bariatric surgery and evaluates different dosing regimens for achievement of pre-defined target exposures.

METHODS

Serial blood samples were collected during surgery with relevant clinical data. Total serum cefoxitin concentrations were measured by chromatographic assay and analysed using a population PK approach with Pmetrics®. The cefoxitin unbound fraction (fu) was estimated. Dosing simulations were performed to ascertain the probability of target attainment (PTA) to achieve cefoxitin fu above minimum inhibitory concentrations (MIC) from surgical incision to wound closure. Fractional target attainment (FTA) was calculated against MIC distributions of common pathogens.

RESULTS

A total of 123 obese patients (median BMI 44.3 kg/m2) were included with 381 cefoxitin concentration values. Cefoxitin was best described by a one-compartment model, with a mean clearance and volume of distribution of 10.9 ± 6.1 L/h and 23.4 ± 10.5 L, respectively. In surgery <2 h, a 2 and a 4 g doses were sufficient for an MIC up to 4 and 8 mg/L (fu 50%), respectively. In prolonged surgery (2-4 h), only continuous infusion enabled optimal PTA for an MIC up to 16 mg/L. Optimal FTAs were obtained against Staphylococcus aureus and Escherichia Coli only when simulating with 50% cefoxitin protein binding (intermittent regimen) and regardless of the protein binding for the continuous infusion.

CONCLUSION

Intermittent dosing regimens resulted in optimal FTAs against susceptible MIC distributions of S. aureus and E. coli when simulating with 50% cefoxitin protein binding. Continuous infusion of cefoxitin may improve FTA regardless of protein binding.

STUDY REGISTRATION

Registration on ClinicalTrials.gov, NCT03306290.

Predictive performance of pharmacokinetic models for target concentration-controlled infusion of cefoxitin as a prophylactic antibiotic in patients with colorectal surgery

We aimed to evaluate the predictive performance of previously constructed free (C_free) and total (C_total) cefoxitin pharmacokinetic models and the possibility of administering cefoxitin via the target‐controlled infusion (TCI) method in clinical practice. Two external validation studies (N = 31 for C_free model, N = 30 for C_total model) were conducted sequentially. Cefoxitin (2 g) was dissolved in 50 mL of normal saline to give a concentration of 40 mg mL⁻¹. Before skin incision, cefoxitin was infused with a TCI syringe pump. Target concentrations of free concentration and total concentration were set to 25 and 80 μg mL⁻¹, respectively, which were administered throughout the surgery. Three arterial blood samples were collected to measure the total and free plasma concentrations of cefoxitin at 30, 60 and 120 min, after the start of cefoxitin administration. The predictive performance was evaluated using four parameters: inaccuracy, divergence, bias and wobble. The pooled median (95% confidence interval) biases and inaccuracies were − 45.9 (−47.3 to −44.5) and 45.9 (44.5 to 47.3) for C_free model (Choi_F model), and − 16.6 (−18.4 to −14.8) and 18.5 (16.7 to 20.2) for C_total model (Choi_T_old model), respectively. The predictive performance of the newly constructed model (Choi_T_new model), developed by adding the total concentration data measured in the external validation, was better than that of the Choi_T_old model. Models constructed with total concentration data were suitable for clinical use. Administering cefoxitin using the TCI method in patients maintained the free concentration above the minimal inhibitory concentration (MIC) breakpoints of the major pathogens causing surgical site infection throughout the operation period.

Influence of the Obesity Phenotype on the Adequacy of Antibiotic Prophylaxis with Cefoxitin for Obese Patients Undergoing Bariatric Surgery: Lessons Learnt and Future Considerations

BACKGROUND AND OBJECTIVES

A high inter-individual variability in pharmacokinetic parameters in obese patients is observed. The objective of this study was to evaluate the effect of obesity parameters on the pharmacokinetics of cefoxitin administered for antibiotic prophylaxis during bariatric surgery.

METHODS

This a secondary analysis of a pharmacokinetic study involving 174 obese patients scheduled for bariatric surgery and receiving a 4-g dose of cefoxitin. Blood samples were collected at incision and wound closure. The total plasma concentrations were assessed utilising a validated high-performance liquid chromatography-tandem mass spectrometry method. The pharmacokinetic and pharmacodynamic target was defined as an estimated free concentration of cefoxitin at the time of wound closure >8 mg/L. Specific evaluated obesity parameters were fat body mass, fat body mass/height², lean body mass, lean body mass/height², visceral adipose tissue and presence of a metabolic syndrome.

RESULTS

A total of 174 patients (median age 47 years) with a majority of women (75.3%) and a median BMI of 44 kg/m² were analysed. The percentage of patients who met the pharmacokinetic and pharmacodynamic target was 85.1%. In the whole population, a tendency to fail to reach the target was observed with a higher lean mass over height² [OR = 0.79; 95% CI (0.62-1.01); P = 0.060]. In the female subgroup, higher lean mass over height² [OR = 0.63; 95% CI (0.41-0.97); P = 0.037] and the presence of a metabolic syndrome [OR = 0.17; 95% CI (0.03-0.83); P = 0.030] were associated with failure to reach the pharmacokinetic and pharmacodynamic target.

CONCLUSION

Obese patients with a higher lean mass and a metabolic syndrome could constitute a subgroup at risk for cefoxitin under-dosage.

Development of a new pharmacokinetic model for target-concentration controlled infusion of cefoxitin as a prophylactic antibiotic in colorectal surgical patients

AIMS

There are several limitations to the existing method of administering cefoxitin as a prophylactic antibiotic, and the limitations may be overcome by applying the target-concentration controlled infusion (TCI) method. Population pharmacokinetic parameters are required to administer cefoxitin by the TCI method. The aim of this study was to construct a new pharmacokinetic model of cefoxitin for the TCI method in colorectal surgical patients.

METHODS

In patients undergoing colorectal surgery, 2 g of cefoxitin was dissolved in 50 mL of saline and administered for 10 minutes prior to skin incision. Arterial blood samples were obtained at preset intervals to measure the total and free plasma concentrations of cefoxitin. Population pharmacokinetic analysis was performed using NONMEM software (ICON Development Solutions, Dublin, Ireland). Additionally, stochastic simulation was used to indirectly evaluate the effectiveness of the two administration methods (standard method vs TCI).

RESULTS

In total, 297 plasma concentration measurements from 31 patients were used to characterize the pharmacokinetics of cefoxitin. A three-compartment mammillary model described the pharmacokinetics of cefoxitin. Body weight and creatinine clearance were significant covariates for clearance. The stochastic simulation showed that when compared with the standard method, the TCI method has a significantly higher fraction of time that the free concentration of cefoxitin is maintained above the minimum inhibitory concentration (P < .001).

CONCLUSIONS

TCI has the potential to become a new infusion method for patient-tailored dosing in surgical patients. To administer cefoxitin via TCI in clinical practice, the newly constructed pharmacokinetic model should undergo proper external validation.

Cost-Effectiveness Analysis of the Prophylactic Use of Ertapenem for the Prevention of Surgical Site Infections after Elective Colorectal Surgery

Standard surgical antimicrobial prophylaxis (SAP) regimens are less effective in preventing surgical site infections (SSIs) due to rising antimicrobial resistance (AMR) rates, particularly for patients undergoing colorectal surgery. This study aimed to evaluate whether ertapenem should be a preferred strategy for the prevention of SSIs following elective colorectal surgery compared to three standard SAP regimens: amoxicillin-clavulanate, cefoxitin, and cefazolin plus metronidazole. A cost-effectiveness analysis was conducted using decision tree models. Probabilities of SSIs and AMR-SSIs, costs, and effects (in terms of quality-adjusted life-years) were considered in the assessment of the alternative strategies. Input parameters integrated real data from the Italian surveillance system for SSIs with data from the published literature. A sensitivity analysis was conducted to assess the potential impact of the decreasing efficacy of standard SAP regimens in preventing SSIs. According to our models, ertapenem was the most cost-effective strategy only when compared to amoxicillin-clavulanate, but it did not prove to be superior to cefoxitin and cefazolin plus metronidazole. The sensitivity analysis found ertapenem would be the most cost-effective strategy compared to these agents if their failure rate was more than doubled. The findings of this study suggest ertapenem should not be a preferred strategy for SAP in elective colorectal surgery.

Quantification of microdialysis related variability in humans: Clinical trial design recommendations

OBJECTIVE

Target-site concentrations obtained via the catheter-based minimally invasive microdialysis technique often exhibit high variability. Catheter calibration is commonly performed via retrodialysis, in which a transformation factor, termed relative recovery (RR), is determined. Leveraging RR values from a rich data set of a very large clinical microdialysis study, promised to contribute critical insight into the origin of the reportedly high target-site variability. The present work aimed (i) to quantify and explain variability in RR associated with the patient (including non-obese vs. obese) and the catheter, and (ii) to derive recommendations on the design of future clinical microdialysis studies.

METHODS

A prospective, age- and sex-matched parallel group, single-centre trial in non-obese and obese patients (BMI=18.7-86.9 kg/m²) was performed. 1-3 RR values were obtained in the interstitial fluid of the subcutaneous fat tissue in one catheter per upper arm of 120 patients via the retrodialysis method (n_RR=1008) for a panel of drugs (linezolid, meropenem, tigecycline, cefazolin, fosfomycin, piperacillin and acetaminophen). A linear mixed-effects model was developed to quantify the different types of variability in RR and to explore the association between RR and patient body size descriptors.

RESULTS

Estimated RR was highest for acetaminophen (69.7%, 95%CI=65.0% to 74.3%) and lowest for piperacillin (40.4%, 95%CI=34.6% to 46.0%). The linear mixed-effects modelling analysis showed that variability associated with the patient (σ=15.9%) was the largest contributor (46.7%) to overall variability, whereas the contribution of variability linked to the catheter (σ=5.55%) was ~1/6 (16.8%). The relative contribution of residual unexplained variability (σ=12.0%, including intracatheter variability) was ~1/3 (36.4%). The limits of agreement of repeated RR determinations in a single catheter ranged from 0.694-1.64-fold (linezolid) to 0.510-3.02-fold (cefazolin). Calculated fat mass affected RR, explaining the observed lower RR in obese (ΔRR_mean= -29.7% relative reduction) versus non-obese patients (p<0.001); yet only 15.8% of interindividual variability was explained by this effect. No difference in RR was found between catheters implanted into the left or right arm (p=0.732).

CONCLUSIONS

Three recommendations for clinical microdialysis trial design were derived: 1) High interindividual variability underscored the necessity of measuring individual RR per patient. 2) The low relative contribution of intercatheter variability to overall variability indicated that measuring RR with a single catheter per patient is sufficient for reliable catheter calibration. 3) The wide limits of agreement from multiple RR in the same catheter implied an uncertainty of a factor of two in target-site drug concentration estimation necessitating to perform catheter calibration (retrodialysis sampling) multiple times per patient. To allow routine clinical use of microdialysis, research efforts should aim at further understanding and minimising the method-related variability. Optimised study designs in clinical trials will ultimately yield more informative microdialysis data and increase our understanding of this valuable sampling technique to derive target-site drug exposure.

Antibiotic prophylaxis with high-dose cefoxitin in bariatric surgery: an observational prospective single center study

BACKGROUND

The optimal dose of cefoxitin for antibiotic prophylaxis in obese patients remains uncertain. We evaluated the adequacy of a 4-gram dosing regimen of cefoxitin against the most frequent pathogens that infect patients undergoing bariatric surgery.

METHODS

This observational prospective study included obese patients who required bariatric surgery and a 4-gram dose of cefoxitin as an antibiotic prophylaxis. Serum concentrations were measured during surgery (incision, wound closure and in case of reinjection). The pharmacokinetic/pharmacodynamic (PK/PD) target was to obtain free cefoxitin concentrations above 4× MIC, from incision to wound closure (100% ƒT_>4xMIC). The targeted MIC was based on the worst-case scenario (the highest ECOFF value of Staphylococcus aureus, Enterobacteriaceae and anaerobic bacteria). The secondary outcomes were the factors related to underdosage.

RESULTS

Two hundred patients were included. The mean age of the patients was 46 (±12) years-old, and the mean BMI was 45.8 (±6.9) kg/m² Bypass surgery was the preferred technique (84%). The percentages of patients who met the PK/PD target (100% fT_>4xMIC) of cefoxitin were 37.3%, 1.1% and 0% for S. aureus, Enterobacteriaceae and anaerobic bacteria, respectively. BMIs below 50 kg/m² (OR 0.29, 95% CI [0.11-0.75], P = 0.0107) and a shorter duration of surgery (OR 0.97, 95% CI [0.95-0.99], P = 0.004) were associated with reaching the target concentrations.

CONCLUSIONS

In obese patients undergoing bariatric surgery, a regimen of 4 grams of cefoxitin led to an inadequate coverage for most common pathogens. A longer surgery duration and BMI over 50 kg/m² increase the risk of underdosage.