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.
No effect of topical ampicillin prophylaxis in elective operations of the colon or rectum.
Whether or not topical application of ampicillin is necessary in patients undergoing elective colorectal operations was investigated. After mechanical preparation, 193 patients received 2 grams of cefotaxime administered intravenously from the start of the operation; patients received two more doses within the next 12 hours. In addition, patients were randomized to receive or not receive prophylaxis against infection of 2 grams of ampicillin in the site of the incision at closure. Twenty-three patients did not complete the study. Wound infection occurred in five of 81 patients who had topical application of ampicillin compared with six of 89 patients who did not receive prophylaxis; the difference was not significant. There were no significant differences in rates of wound dehiscence, intra-abdominal abscess or anastomotic leakage. Escherichia coli and Bacteroides fragilis were the predominant microorganisms isolated. Thus, topical application of ampicillin did not lower the wound infection rate when there was a preoperative antibiotic administered intravenously.