Metronidazole need not be combined with an aminoglycoside when used for prophylaxis in elective colorectal surgery.

A prospective randomized controlled study has compared prophylactic intravenous metronidazole alone with the combination of metronidazole and gentamicin in 100 patients having elective colorectal surgery. There was no significant difference in mortality, infection, dehiscence or postoperative stay between the antibiotic groups. Postoperative sepsis was almost entirely due to aerobic organisms but was associated with minimal morbidity. A significantly higher rate of anastomotic dehiscence and postoperative infection was seen where the quality of bowel preparation was judged to be poor.