Prophylactic regimens in colorectal surgery. Comparison between metronidazole used alone or in combination with either ampicillin or doxycycline.

Sixteen hospitals are participating in this study, that started in October 1982 and will be concluded when 456 patients have been admitted. The study includes patients eligible for elective colorectal surgery. Inclusion criteria, surgical techniques, definition of recognizable infection, sampling of specimens for bacteriological investigations, bacteriologic techniques, and evaluation criteria were standardized. Patients were divided into 2 main groups. Patients in Group 1 received either a single intravenous dose of 1500 mg metronidazole or this dose was combined with a single, intravenous dose of 6 g ampicillin. Patients in group 2 received either a single intravenous dose of 1500 mg metronidazole or this dose combined with a single intravenous dose of 400 mg doxycycline. Dosage regimens were allocated randomly. The current results concern 136 patients. Postoperative infections were seen in 6.7% of the patients receiving metronidazole alone, and 2.9% of the patients receiving metronidazole + ampicillin (Group 1). In Group 2, postoperative infection occurred in 17.1% of the patients receiving metronidazole alone, and in 2.7% of those receiving metronidazole + doxycycline.