Antibiotic prophylaxis with cefoxitin in colorectal surgery: effect on the colon microflora and septic complications--a clinical model for prediction of the benefit and risks in using a new antibiotic in prophylaxis.

Cefoxitin was administered parenterally in doses of 2 g, every six hours for two days, to 20 patients undergoing colorectal surgery. Blood and fecal specimens were obtained for five days for analysis of cefoxitin concentrations. Tissue samples from the gut wall were obtained at surgery. The maximum serum concentrations during surgery varied between 25 and 100 microgram/ml, and the cefoxitin concentrations for the fecal samples were 1.5-35 microgram/g and for the tissue samples, 2.0-50 microgram/g. Fecal samples for cultivation of aerobic and anaerobic bacteria were also obtained daily during the first five days, and after 14 day after operation. Pronounced changes in the microflora occurred during the investigation period. Among the aerobic bacteria, cefoxitin-sensitive Escherichia coli and other enterobacteria decreased markedly while cefoxitin-resistant enterococci, Pseudomonas and Enterobacter proliferated during the antibiotic prophylaxis period. Among the anaerobic bacteria, Bacteroides fragilis and other Gram-negative bacteria decreased significantly. However, after the antibiotic administration period, all cefoxitin-resistant strains decreased while the suppressed E. coli and B. fragilis strains increased. In one patient, a minor postoperative infection caused by a cefoxitin-resistant strain of Pseudomonas aeruginosa was observed.