Intravenously administered ciprofloxacin is partially secreted into the intestinal lumen and thereby eliminates fecal Enterobacteriaceae, Sucralfate inhibits the antimicrobial activity of ciprofloxacin by chelate binding. In a prospective study, we investigated the impact of intravenous ciprofloxacin on the intestinal microflora during oral administration of sucralfate. A total of 45 stool specimens were analyzed in to hospitalized patients who were treated with zoo mg of ciprofloxacin i.v. bid,Ten patients concomitantly received 1 g sucralfate p,o, tid (group A). After more than 3 days of i.v. ciprofloxacin, the mean fecal ciprofloxacin concentration was 185.3 +/- 158.7 mu g/g in patients of group A and 108.7 +/- 76.9 mu g/g in patients without concurrent sucralfate (group B), There was no significant difference in mean fecal ciprofloxacin levels between both groups (Wilcoxon's test). Enterobacteriaceae were below the threshold of detection (10(2) cfu/g) in all patients of group B after 3 days of treatment whereas small numbers were found in only 2 samples of patients of group A (10(4) cfu/g). Intravenous ciprofloxacin eliminates or largely reduces intestinal Enterobacteriaceae irrespective of concurrent administration of sucralfate.