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.
Systemic prophylaxis with gentamicin-metronidazole in appendicectomy and colorectal surgery: a prospective controlled clinical study.
A prospective, randomized, clinical study was carried out in 188 patients undergoing appendicectomy or colorectal surgery to test the efficacy of prophylactic, parenterally-administered antibiotics in the prevention of infection. The results show the effectiveness of the association gentamicin-metronidazole (9.4% of infections), compared to the control group with no antibiotics (39.1% of infections), X2 = 14.1; P less than 0.001).