Serum levels of prophylactic cefazolin during cardiopulmonary bypass surgery

Background. Controversy exists regarding the appropriate prophylactic dose of cefazolin for coronary artery bypass grafting (CABG) surgery requiring cardiopulmonary bypass (CPB) because the effect of CPB on serum drug levels is poorly understood. Current standards of prophylaxis are based primarily on empiric studies. Few studies have attempted to quantify serum cefazolin levels in either cardiac or noncardiac surgeries. This study was conducted to measure and assess the adequacy of the intraoperative serum levels of prophylactic cefazolin in CPB surgery. Methods. This prospective study serially measured six intraoperative serum cefazolin levels in 10 subjects undergoing elective and urgent CABG surgery. We compared the serum levels with the minimum inhibitory concentrations (MIC90) for the most common organisms causing postoperative infection. Results. Serum-free cefazolin levels fluctuated considerably during the operation but remained above the MIC90 for Staphylococcus aureus and S. epidermidis. The serum levels fell below the MIC90 for Enterobacter, Serratia, Escherichia coli, and Proteus mirabilis. Conclusions. Serum cefazolin levels during CPB remained consistently above the MIC for two of the three main organisms causing postoperative infection but were suboptimal for the remainder. Additional studies are needed,to assess the intraoperative serum levels of single-dose cefazolin prophylaxis and to explore alternate dosing methods that minimize intraoperative fluctuations in serum cefazolin levels.