The pharmacokinetics of a single dose of gentamicin (4 mg/kg) as prophylaxis in cardiac surgery requiring cardiopulmonary bypass

Background: Cardiopulmonary bypass has complex effects on drug pharmacokine tics, which is important when considering the use of once-daily aminoglycos ide regimens during cardiac surgery. Aim: To study the effects of cardiopul monary bypass on the pharmacokinetics of a single dose of gentamicin (4 mg/ kg), Patients and methods: Nine patients undergoing valve replacement surge ry were given a single dose of gentamicin (4 mg/kg) at induction of anaesth esia and blood was taken for assay at 0, 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 10, 16, 22 and 24 h following administration. The mean (range) gentamicin C-max was 18.7 (12.4-26.3) mg/litre, Three patients had concentrations of gentam icin after 24 h of >1 mg/litre. During cardiopulmonary bypass, the mean (ra nge) gentamicin half-life (t(1/2)) was 5.1 (2.0-15.1) h and postbypass the t(1/2) was 7.1 (3.0-13.9) h. Conclusion: There is significant correlation b etween the elimination t(1/2) and length of cardiopulmonary bypass (r = 0.8 9, P < 0.01). These results suggest that gentamicin excretion is delayed fo llowing cardiopulmonary bypass so that with dose regimens of >4 mg/kg there is a risk of toxicity (C) 1999 The International Society for Cardiovascula r Surgery. Published by Elsevier Science Ltd. All rights reserved.