The influence of norfloxacin on the intestinal bacterial flora

We studied the effect of norfloxacin (NFLX), a pyridonecarboxylic acid derivative antimicrobial agent, on intestinal bacterial flora in pediatric patients. The subjects were 4 boys and 1 girl aged from 4 years 2 months to 11 years 8 months, and their body weight ranged from 17-34 kg. NFLX was administered at a dose of 2.9-5.3 mg/kg, 3 times a day for 5-9 days. We quantified and identified bacterial species in faces, and measured fecal concentrations of NFLX and Clostridium difficile D-1 antigen before, during and after the administration of NFLX. Changes in fecal flora during treatment varied among subjects. Of the aerobes, Enterobacteriaceae decreased significantly in all cases. Of the anaerobes, Bifidobacterium tended to decrease in some cases, but no remarkable changes were observed in other main anaerobes, such as Bacteroidaceae. So changes in the total count of anaerobes were small. There was no case in which glucose non-fermenting Gram-negative rods and fungi became predominant species. Neither C. difficile nor C. difficile D-1 antigen were detected. NFLX, at concentrations of 96-480 μg/g, was detected in the feces in all cases and in some cases, even 2-6 days after the end of dosing at 2.20-7.15 μg/g. Based on our findings, we consider NFLX to be a drug with relatively little effect on intestinal bacterial flora other than Enterobacteriaceae in pediatric patients.