Effect of Metronidazole and Sulfasalazine on the Normal Human Faecal Flora

Abstract

Nine healthy individuals were treated with metronidazole (Flagyl®) for 2 weeks and sulfasalazine (Salazopyrin®) for 2 further weeks or inversely after randomization. Before, at the day for cross-over, and at the end of treatment, quantitative and qualitative studies of the aerobic and anaerobic faecal bacteria and plasma concentration studies of the drugs were performed. The total counts of aerobic and anaerobic bacteria were in close agreement with those reported by others. A comparison between pretreatment samples and those taken at the end of treatment showed a significant or almost significant increase in the count of faecal streptococci (P = 0.03) and of Escherichia coli (P = 0.06) in subjects treated with metronidazole, but not with sulfasalazine. However, the changes in the anaerobic bacterial flora reported during treatment in patients with Crohn's disease with the same drugs were not observed among the healthy individuals.