A randomized evaluation of single dose chemoprophylaxis in elective colorectal surgery--a comparison between metronidazole and doxycycline.

In a prospective, randomized blind study either 400 mg doxycycline or 1500 mg metronidazole were given intravenously in a single preoperative dose to 147 consecutive patients before elective colorectal surgery. Septic complications mainly caused by a mixed flora of aerobes and anaerobes occurred in 13% of the patients in the doxycycline group. Septic complications occurred in 29% of the patients in the metronidazole group and were caused by E. coli and coliform rods. Bacteriological studies showed a marked reduction of anaerobes in peroperative samples in this group. Most postoperative infections were superficial and mild wound infections. The inactivity of metronidazole against aerobes resulted in an unacceptable high frequency of septic complications caused by aerobic bacteria. For chemoprophylaxis metronidazole should therefore be combined with an antimicrobial agent against aerobic bacteria.