Antibiotics covering aerobic and aerobic bacteria should be delivered orally and intravenously prior to colorectal surgery.  Antibiotics delivered within this framework will reduce the risk of postoperative SWI by at least 75%.  Further research is required to establish the optimal timing and duration of dosing, and frequency of longer-term adverse effects such as Clostridium difficile pseudomembranous colitis.
Single dose imipenem-cilastatin compared with three doses of cefuroxime and metronidazole as prophylaxis in elective colorectal surgery: a prospective randomized study.
A prospective randomized study was performed with 61 patients undergoing elective surgery for colorectal cancer, to evaluate the prophylactic effect of two different parenteral antibiotic regimens. All patients were randomly allocated into two groups, comparable in age, sex, nutritional status and operative procedures. The patients in Group A (n. 31) received 1 g i.v. of imipenem-cilastatin at induction of anesthesia. Patients in Group B (n. 30) were given cefuroxime (1.5 g i.v.) plus metronidazole (0.5 g i.v.) at the time of anesthesia and two other administrations of the combined antibiotics (cefuroxime 0.75 g plus metronidazole 0.5 g i.v.) every 8 hours. The severity of sepsis was evaluated according to the scoring system proposed by Elebute and Stoner. No significant differences were found in terms of the rate of surgical infections: 9% in Group A and 16% in Group B. Infections not of surgical origin were found only in Group B (10.4%). These data suggest that a single dose of intravenous imipenem-cilastatin appears to be as effective as three doses of cefuroxime and metronidazole as prophylaxis against infection in elective colorectal surgery.