Duration of antibiotic prophylaxis. An experimental study.

An animal wound model was used to evaluate single dose cefazolin, multiple dose cefazolin, and single dose cefonicid in the prevention of wound infection. Incisions made in Swiss-Webster mice were contaminated with either Staph. aureus (1.94 X 10(8) colony forming units) or E. coli (4.39 X 10(8) colony forming units). Five experimental groups were studied. Group I encompassed control animals given saline solution, Group II animals given 10 mg cefazolin preoperatively, Group III animals given 10 mg of cefazolin preoperatively and postoperatively, Group IV animals given 10 mg of cefonicid preoperatively, and Group V animals given 20 mg of cefonicid preoperatively. All medications were given by intraperitoneal injection. Antibiotics were given 1 hour before operation. Postoperative doses were given 4 hours after operation. Incisions were opened 48 hours after surgery and wound bacterial concentrations were determined. After both Staph. aureus and E. coli contamination, each of the four cephalosporin regimens significantly reduced the mean wound bacterial concentrations compared with that of the control animals (p less than 0.001). Each of the four cephalosporin regimens also significantly reduced the number of infected wounds compared with that of the control subjects (p less than 0.001). No significant differences were noted among the four antibiotic regimens with respect to mean wound bacterial concentration or infection rate. In the context of this model, a single dose of cefazolin seems to be equally effective as multiple doses of the drug for surgical prophylaxis. Extended half-life cephalosporins, like cefonicid, do not appear to be more effective than a single dose of cefazolin, which is a much less expensive antibiotic.