Effect of New Quinolones on the Human Gastrointestinal Microflora

During the last years, the effect of new quinolones--ciprofloxacin, norfloxacin, ofloxacin, and pefloxacin--on the human microflora has been studied. This review article summarizes the published data concerning these studies. The results show that the oropharyngeal flora is only slightly or not at all affected by the quinolones. All new quinolones have a similar effect on the normal intestinal flora. The gram-negative aerobic flora is strongly suppressed during administration of quinolones, while the gram-positive flora is only slightly affected. The anaerobic microflora is almost not at all affected by the administration. The emergence of resistant bacterial strains is uncommon, although one investigation showed increased MIC values for anaerobes during ciprofloxacin administration. Replacement by yeasts or other inherently resistant microorganisms does not often seem to be a problem. High concentrations of the new quinolones are reached in feces; values between 100 and 2,200 mg/kg are reported. Since the new quinolones do not cause marked ecologic disturbances in the intestinal microflora, they may be suitable for selective decontamination in immunocompromised patients and for treatment of bacterial intestinal infections.