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 chemoprophylaxis in elective colorectal surgery. A comparison between doxycycline plus metronidazole and doxycycline.
In a prospective, randomized double-blind study either 400 mg of doxycycline + 1500 mg of metronidazole (D + M) or 400 mg of doxycycline (D) alone were given intravenously as a single preoperative dose to patients admitted for elective colorectal surgery. A comparison of the rate of postoperative septic complications was made. After excluding drop-out patients, 261 patients remained for evaluation. In 135 patients with D + M treatment there were four postoperative septic complications (3.0%). In 126 patients with D treatment 20 septic complications related to the surgical procedure occurred (15.9%). The difference is highly significant (p less than 0.005). Most postoperative infections were superficial wound infections (14 of 24 patients), and the mean hospital stay in the two treatment groups was equal. Bacteriologic studies showed a highly significant reduction in anaerobes in cultures from perioperative intra-abdominal fluid in the D + M treatment group. The study has thus showed that the addition of metronidazole, an efficient agent against anaerobic bacteria, to an antimicrobial agent against aerobic bacteria significantly reduces postoperative septic complications in elective colorectal surgery.