The effect of cardiopulmonary bypass (CPB) on the disposition of vancomycin (15 mg/kg) and of netilmicin (3 mg/kg) was studied in 10 adults. The concentration-time profile of the drug in serum and renal clearance were characterized pre-CPB, during CPB, and post-CPB. Vancomycin and netilmicin exhibited initial decreases in mean concentrations in serum of 4.0 mg/liter (16.8%) and 2.2 mg/liter (29.1%), respectively, upon initiation of CPB. Netilmicin concentrations in serum rebounded to a mean of 0.6 mg/liter (15.4%) within 90 min on CPB and then continuously decreased. Vancomycin concentrations in serum demonstrated a rebound increase of 2.3 mg/liter (23.5%) at the end of CPB when the aorta was unclamped. Mean renal clearance throughout CPB was decreased for vancomycin (58.4 to 43.4 ml/min per mi2) and netilmicin (53.4 to 31.5 ml/min per m2). The rebound in vancomycin concentration in serum strongly correlated with the length of time between unclamping the aorta and coming off CPB (r = 0.94), as well as with the increase in temperature upon rewarming (r = 0.92).Antimicrobial prophylaxis for cardiopulmonary bypass (CPB) surgery is routinely prescribed to prevent endocarditis or sternal and costochondral infections (7, 26). Selection of an appropriate antibiotic is directed against Staphylococcus aureus and Staphylococcus epidermidis, which account for the majority of bacterial infections, and also against the gram-negative bacilli (2, 3, 7, 26). The increasing incidence of methicillin-resistant staphylococci has led to the recommendation that vancomycin be administered prophylactically for cardiothoracic surgery in hospitals in which methicillin-resistant staphylococci are prevalent (3,15,16). Aminoglycosides have been recommended for prophylaxis against the gram-negative pathogens on the cardiac valves and the sternum and for some prophylactic effect against staphylococci (16).Many physiologic changes occur in patients placed on CPB. These changes, including decreased cardiac output and organ perfusion, can alter drug absorption, distribution, metabolism, and excretion (13,14). Studies with prophylactic vancomycin and netilmicin in CPB surgery are very limited. Only two reports have examined vancomycin concentrations in serum during CPB surgery, and both sought to determine appropriate dosing, rather than drug disposition (4, 10).One published report of aminoglycoside prophylaxis in open-heart surgery has addressed netilmicin concentrations in pericardial fluid, atrial appendage, and serum but only in the intraoperative phase of CPB (27). Therefore, this study was designed to investigate what effect CPB surgery has on the disposition of two renally excreted prophylactic antibiotics, vancomycin and netilmicin, before, during, and after CPB.
MATERIALS AND METHODSA total of 10 adult patients scheduled for elective coronary artery bypass grafting or cardiac valve replacement surgery requiring CPB were studied. All patients gave written informed consent to participate in this protocol, which was * Corresponding author....