EFFECTS OF CARDIOPULMONARY BYPASS ON VANCOMYCIN PLASMA-CONCENTRATION DECAY

The objective of the study was to investigate possible changes in vanc omycin serum levels induced by cardio-pulmonary bypass (CPB). Ten card iac patients (seven males, three females, aged between 56 and 81), who underwent cardiac surgery requiring CPB, took part in the study. Vanc omycin (15 mg kg(-1)) was intravenously infused over 60 min before ana esthesia and blood samples were taken at appropriate times after drug administration (0, 0.5, 1, 6, 8 h), after starting CPB (0, 5, 30 and 6 0 min) and after aortic unclamping (0, 5, 30, 60, 120 min). Drug serum concentrations were determined by means of a fluorescence polarizatio n immunoassay. The area under the concentration-time curve (AUC) measu red during CPB were compared with the AUC extrapolated in the same int erval by fitting a two-compartment pharmacokinetic model to drug conce ntrations obtained before and after CPB. Five minutes after starting C PB vancomycin serum levels decreased, on average, by 40.9% and remaine d steadily lower than the expected values over the next 60 min. In the same interval, the measured AUC was 31.7% lower than the expected AUC . In no instance did serum levels fall below the MIC for most common p athogens (1-2 mg l(-1)). At aortic unclamping serum levels slightly re bounded but tended to remain lower than the expected concentrations ov er the next 120 min. In conclusion, during CPB vancomycin serum levels invariably decreased but, at the dose employed (15 mg kg(-1)), remain ed in a potentially effective range for antimicrobial prophylaxis. (C) 1998 The Italian Pharmacological Society.