Pharmacokinetics of Cefepime in Children on Extracorporeal Membrane Oxygenation External Model Validation, Model Improvement and Dose Optimization

Background: Cefepime is a first-line therapy for Gram-negative infections in children on extracorporeal membrane oxygenation. Cefepime pharmacokinetics (PK) in children on extracorporeal membrane oxygenation still needs to be better established. Methods: This was a prospective single-center PK study. A maximum of 12 PK samples per patient were collected in children <18 years old on extracorporeal membrane oxygenation who received clinically indicated cefepime. External validation of a previously published population PK model was performed by applying the model in a new data set. The predictive performance of the model was determined by calculating prediction errors. Because of poor predictive performance, a revised model was developed using NONMEM and a combined data set that included data from both studies. Dose-exposure simulations were performed using the final model. Optimal dosing was judged based on the ability to maintain free cefepime concentrations above the minimal inhibitory concentration (MIC) for 68% and 100% of the dosing interval. Results: Seventeen children contributed 105 PK samples. The mean (95% CI) and median (interquartile range) prediction errors were 33.7% (19.8-47.7) and 17.5% (-22.6 to 74.4). A combined data set was created, which included 33 children contributing 310 PK samples. The final improved 2-compartment model included weight and serum creatinine on clearance and oxygenator day and blood transfusion on volume of the central compartment. At an MIC of 8 mg/L, 50 mg/kg/dose every 8 hours reached target concentrations. Conclusions: Dosing intervals of 8 hours were needed to reach adequate concentrations at an MIC of 8 mg/L. Longer dosing intervals were adequate with higher serum creatinine and lower MICs.