Flucloxacillin concentration in serum and wound exudate during open heart surgery

Per-operative serum and wound fluid concentrations achieved by two flucloxacillin dosage regimens were measured in twelve patients undergoing open heart surgery. One 500 mg bolus dose given after the induction of anaesthesia in six patients resulted in adequate serum concentrations (means decreasing from 69 to 9 mg/l) during surgery, but low wound fluid concentrations (mean 4.6 mg/l, range less than 2-7.8 mg/l) at the time of closure. An additional 500 mg bolus dose given after bypass in six further patients gave more satisfactory wound concentrations (mean 16 mg/l, range 8.6-22.5 mg/l). Disc absorption is a useful technique for assaying antibiotics in wound fluid, but the results are difficult to interpret since they represent a sum of concentrations in a complex and changing mixture of interstitial tissue fluid, blood and cardioplegia solution.