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.
Comparison of metronidazole with doxycycline prophylaxis in elective colorectal surgery. A prospective, randomized multicentre study.
In a series of 157 patients undergoing elective colorectal surgery, metronidazole or doxycycline was given to prevent infectious complications. The prophylaxis was started just before the operation and was administered for a total of three days. Excluding mild, negligible infections, 39 (25%) of the 157 patients had infectious complications, 23 from the metronidazole group (28%) and 16 from the doxycycline group (21%). The type of infection varied according to the medication. In four cases of the metronidazole group and 16 of the doxycycline group, anaerobic bacteria were found. The corresponding figures for aerobes were 36 and 20. Doxycycline thus was significantly more effective in preventing complications in general, but metronidazole gave superior protection against anaerobes.