Effect of aztreonam on the colon microflora in patients undergoing colorectal surgery

Aztreonam was given intravenously at a dose of 1 g at induction of anaesthesia, followed by subsequent doses of 1 g at eight hour intervals during 48 hours to 20 patients undergoing colorectal surgery. A series of serum and faecal specimens were taken for analysis of aztreonam concentrations. Tissue samples from the gut wall were taken at surgery. The maximum serum concentrations (mean value 114.7 mg/l) during surgery were reached 15 minutes after aztreonam administration. The aztreonam concentration in the tissue samples varied from 4.1-28.3 mg/kg and the concentration in the faecal samples from 0.4-34.4 mg/kg. Faecal samples were also collected during the investigation period for cultivation of aerobic and anaerobic bacteria. Enterobacteria were suppressed significantly during the prophylaxis period and there was a significant increase of staphylococci in ten of the patients. Three of these patients developed postoperative wound infections with staphylococci. Among the anaerobic bacteria, only minor changes were observed during the same period. After two weeks, the microflora was normalized in all patients. Five postoperative infections including an anastomose dehiscence in one patient occurred.