Target-Controlled Infusion of Cefepime in Critically Ill Patients

Population pharmacokinetic model of cefepime for critically ill adults: a comparative assessment of eGFR equations

Cefepime exhibits highly variable pharmacokinetics in critically ill patients. The purpose of this study was to develop and qualify a population pharmacokinetic model for use in the critically ill and investigate the impact of various estimated glomerular filtration rate (eGFR) equations using creatinine, cystatin C, or both on model parameters. This was a prospective study of critically ill adults hospitalized at an academic medical center treated with intravenous cefepime. Individuals with acute kidney injury or on kidney replacement therapy or extracorporeal membrane oxygenation were excluded. A nonlinear mixed-effects population pharmacokinetic model was developed using data collected from 2018 to 2022. The 120 included individuals contributed 379 serum samples for analysis. A two-compartment pharmacokinetic model with first-order elimination best described the data. The population mean parameters (standard error) in the final model were 7.84 (0.24) L/h for CL1 and 15.6 (1.45) L for V1. Q was fixed at 7.09 L/h and V2 was fixed at 10.6 L, due to low observed interindividual variation in these parameters. The final model included weight as a covariate for volume of distribution and the eGFRcr-cysC (mL/min) as a predictor of drug clearance. In summary, a population pharmacokinetic model for cefepime was created for critically ill adults. The study demonstrated the importance of cystatin C to prediction of cefepime clearance. Cefepime dosing models which use an eGFR equation inclusive of cystatin C are likely to exhibit improved accuracy and precision compared to dosing models which incorporate an eGFR equation with only creatinine.

Population pharmacokinetics and target attainment analyses to identify a rational empirical dosing strategy for cefepime in critically ill patients

OBJECTIVES

We aimed to identify rational empirical dosing strategies for cefepime treatment in critically ill patients by utilizing population pharmacokinetics and target attainment analysis.

PATIENTS AND METHODS

A prospective and opportunistic pharmacokinetic (PK) study was conducted in 130 critically ill patients in two ICU sites. The plasma concentrations of cefepime were determined using a validated LC-MS/MS method. All cefepime PK data were analysed simultaneously using the non-linear mixed-effects modelling approach. Monte Carlo simulations were performed to evaluate the PTA of cefepime at different MIC values following different dose regimens in subjects with different renal functions.

RESULTS

The PK of cefepime in critically ill patients was best characterized by a two-compartment model with zero-order input and first-order elimination. Creatinine clearance and body weight were identified to be significant covariates. Our simulation results showed that prolonged 3 h infusion does not provide significant improvement on target attainment compared with the traditional intermittent 0.5 h infusion. In contrast, for a given daily dose continuous infusion provided much higher breakpoint coverage than either 0.5 h or 3 h intermittent infusions. To balance the target attainment and potential neurotoxicity, cefepime 3 g/day continuous infusion appears to be a better dosing regimen than 6 g/day continuous infusion.

CONCLUSIONS

Continuous infusion may represent a promising strategy for cefepime treatment in critically ill patients. With the availability of institution- and/or unit-specific cefepime susceptibility patterns as well as individual patients' renal function, our PTA results may represent useful references for physicians to make dosing decisions.

Clinical Pharmacokinetics and Pharmacodynamics of Cefepime

Cefepime is a broad-spectrum fourth-generation cephalosporin with activity against Gram-positive and Gram-negative pathogens. It is generally administered as an infusion over 30-60 min or as a prolonged infusion with infusion times from 3 h to continuous administration. Cefepime is widely distributed in biological fluids and tissues with an average volume of distribution of ~ 0.2 L/kg in healthy adults with normal renal function. Protein binding is relatively low (20%), and elimination is mainly renal. About 85% of the dose is excreted unchanged in the urine, with an elimination half-life of 2-2.3 h. The pharmacokinetics of cefepime is altered under certain pathophysiological conditions, resulting in high inter-individual variability in cefepime volume of distribution and clearance, which poses challenges for population dosing approaches. Consequently, therapeutic drug monitoring of cefepime may be beneficial in certain patients including those who are critically ill, have life-threatening infections, or are infected with more resistant pathogens. Cefepime is generally safe and efficacious, with a goal exposure target of 70% time of the free drug concentration over the minimum inhibitory concentration for clinical efficacy. In recent years, reports of neurotoxicity have increased, specifically in patients with impaired renal function. This review summarizes the pharmacokinetics, pharmacodynamics, and toxicodynamics of cefepime contemporarily in the setting of increasing cefepime exposures. We explore the potential benefits of extended or continuous infusions and therapeutic drug monitoring in special populations.

Prospective assessment of breakthrough infections and neurotoxicity and their association with cefepime trough concentrations in patients with febrile neutropenia

Cefepime is a first-line antibiotic for the treatment of febrile neutropenia (FN) in haematological cancer patients. Therapeutic drug monitoring (TDM) of cefepime is frequently advocated. However, it remains unclear what range of concentrations should be targeted for maximal efficacy and minimal toxicity. Therefore, we examined the relationship between cefepime exposure and clinical efficacy or neurotoxicity in FN patients. This prospective, observational, single-centre study included all adult hospitalised patients presenting with FN at the haematology ward and treated with cefepime from August 2019 until October 2020. Primary outcomes were incidence of breakthrough infection and neurotoxicity and their relationship with free cefepime serum trough concentrations. A total of 76 patients were included, contributing 96 cefepime treatment courses. The median (interquartile range) estimated glomerular filtration rate according to the Chronic Kidney Disease Epidemiology Collaboration equation (eGFR_CKD-EPI) and free cefepime trough concentration were 101 (85-112) mL/min/1.73m² and 8.6 (4.9-16.2) mg/L, respectively. Interpatient and intrapatient variability in cefepime trough concentrations was largely explained by renal function. No cefepime-related breakthrough infections occurred during cefepime treatment. Neurotoxicity, probably induced by cefepime administration, occurred during 6/96 (6.3%) treatment courses. Patients with neurotoxicity showed a significant trend for higher trough concentrations (median 15.4 mg/L vs. 8.6 mg/L; P < 0.001). This study provides real-world clinical data showing that high cefepime dosage is efficacious and safe in FN patients. Routine TDM does not appear to be needed in FN patients with preserved renal function. However, TDM might be reserved for FN patients at high risk of cefepime-induced neurotoxicity or when intended to cover pathogens with a minimum inhibitory concentration >1 mg/L.

A personalised approach to antibiotic pharmacokinetics and pharmacodynamics in critically ill patients

Critically ill patients admitted to intensive care unit (ICU) with severe infections, or those who develop nosocomial infections, have poor outcomes with substantial morbidity and mortality. Such patients commonly have suboptimal antibiotic exposures at routinely used antibiotic doses related to an increased volume of distribution and altered clearance due to their underlying altered physiology. Furthermore, the use of extracorporeal devices such as renal replacement therapy and extracorporeal membrane oxygenation in these group of patients also has the potential to alter in vivo drug concentrations. Moreover, ICU patients are likely to be infected with less-susceptible pathogens. Therefore, one potential contributing cause to the poor outcomes observed in critically ill patients may be related to subtherapeutic antibiotic exposures. Newer concepts include the clinician considering optimised dosing based on a blood antibiotic exposure defined by pharmacokinetic modelling and therapeutic drug monitoring, combined with a knowledge of the antibiotic penetration into the site of infection, thereby achieving optimal bacterial killing. Such optimised dosing is likely to improve patient outcomes. The aim of this review is to highlight key aspects of antibiotic pharmacokinetics and pharmacodynamics (PK/PD) in critically ill patients and provide a PK/PD approach to tailor antibiotic dosing to the individual patient.

Assessment of cefepime toxicodynamics: comprehensive examination of pharmacokinetic/pharmacodynamic targets for cefepime-induced neurotoxicity and evaluation of current dosing guidelines

BACKGROUND

Cefepime-induced neurotoxicity (CIN) is an increasingly reported adverse event; however, the toxicity threshold remains unclear. This study was conducted to provide a comprehensive examination of the most appropriate threshold for CIN, and evaluate the ability of current dosing regimens to attain therapeutic targets.

METHODS

Data of the incidence of CIN and cefepime plasma concentrations were collected retrospectively from patients administered cefepime. Population pharmacokinetic modelling was used to determine daily cefepime trough concentration (C_min), maximum serum concentration and area under the concentration-time curve. The ability of each pharmacokinetic parameter to predict CIN was evaluated using receiver operating characteristic (ROC) curves, from which optimal toxicity thresholds were determined. Pharmacokinetic simulation was used to evaluate the ability of cefepime dosing guidelines to meet established efficacy targets, whilst maintaining exposure below the determined CIN threshold.

RESULTS

In total, 102 cefepime courses were evaluated, with CIN reported in 10. ROC analyses showed that all cefepime pharmacokinetic parameters were strongly predictive of CIN. C_min of 49 mg/L was identified as the optimal toxicity target, based on its predictive ability (0.88, 95% confidence interval 0.758-0.999, P<0.001) and ease of clinical use. Assessment of cefepime dosing regimens predicted that only 29% of simulated patients achieve therapeutic targets, with patients with impaired renal function more likely to exhibit subtherapeutic concentrations (89%), and patients with normal renal function likely to have potentially toxic exposure (64%).

CONCLUSIONS

The findings from this study provide evidence that cefepime exposure is highly predictive of CIN, with C_min of 49 mg/L being the most appropriate toxicity threshold. Further research is required to optimize cefepime dosing in the context of this therapeutic target.

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.