Antibacterial activity of norfloxacin in the gastrointestinal tracts of rats.

The capacities of norfloxacin (MK-0366) and neomycin to reduce the numbers of bacteria in the gastrointestinal tracts of rats were evaluated. Results of a 3-day treatment with norfloxacin were compared with those of a 3-day treatment with neomycin. Both drugs significantly decreased gram-negative and gram-positive bacteria. Norfloxacin effected a significantly greater reduction in numbers of gram-negative bacteria than did neomycin. Norfloxacin also significantly increased the number of anaerobic bacteria. Although neomycin reduced gram-positive bacteria more effectively than did norfloxacin, this difference between the two drugs was not significant. Norfloxacin merits further study for potential as a bowel sterilant.