Objectives: Although clinical practice guidelines recommend standard cefazolin antimicrobial prophylaxis (AP) dosing for cardiac surgery, limited data exist as to whether adequate concentrations are achieved in this patient population. The goal of our study was to characterize intraoperative cefazolin concentrations particularly at wound closure with regards to maintaining target cefazolin closure concentrations ≥40 mg/L.
Methods: Adults undergoing cardiac surgery with cardiopulmonary bypass (CPB) and receiving cefazolin AP according to protocol were studied. Blood samples were collected after the preoperative cefazolin dose, prior to intraoperative cefazolin doses and at wound closure. Intraoperative trough and closure concentrations were characterized and evaluated against a target threshold of ≥ 40 mg/L (≥8 mg/L unbound, assuming 80% protein binding).
Results: Fifty-five subjects (64.9 ± 10.4 years, 89.7 ± 16.5 kg, CLCR >50 mL/min/72 kg) completed the study. Total cefazolin concentrations were <40 mg/L in 40% (12 of 30) of intraoperative trough samples and 9.8% (5 of 51) of closure samples. Below-target concentrations at some time during surgery were documented in 30.9% (17 of 55) of subjects. In multivariate analyses, lower body weight (P = 0.027) and shorter duration of surgery (P = 0.045) were significant predictors of closure concentrations <40 mg/L. A total cefazolin exposure (preoperative and intraoperative doses) of ≥ 7.6 mg/kgdosing weight for every hour of surgery (intermittent dosing) was required to achieve target closure concentrations.
Conclusions: The standard cefazolin AP regimen was not reliable in maintaining target closure concentrations ≥40 mg/L in patients with normal renal function undergoing elective cardiac surgery with CPB. The findings supported a cefazolin AP regimen consisting of at least 2 g preoperatively and every 3 h during surgery.