Single-dose intravenous metronidazole v. doxycycline prophylaxis in colorectal surgery. An open prospective,...

In an open prospective, randomized study of antimicrobial prophylaxis in colorectal surgery, using a single intravenous dose, metronidazole (1 g) was more effective than doxycycline (0.2 g). The difference in infection rates (2/41 = 5% v. 7/33 = 21%) was statistically significant. Prolonged administration of either agent (2-7 days) yielded results comparable to those with single doses. Five emergency cases were admitted to the study. In two of them, a metronidazole-based therapeutic regimen prevented postoperative infection, whereas infection occurred in all 3 patients given doxycycline therapy. The total infection rate after elective surgery was 4% with metronidazole and 25% with doxycycline prophylaxis. The infections in the metronidazole group were superficial and caused by Escherichia coli, whereas half of the infections in the doxycycline group were intra-abdominal and due to intestinal aerobic and/or anaerobic bacteria. In contrast to doxycycline, therefore, metronidazole prevented postoperative anaerobic infection and was associated with low incidence of aerobic infection.