Comparative effects of levofloxacin and ofloxacin on the normal oral and intestinal microflora.

The aim of the study was to study the ecological effects of levofloxacin, compared to that of ofloxacin, on the oral and intestinal human microflora. 10 healthy volunteers received levofloxacin (500 mg) and 10 subjects were given ofloxacin (400 mg) perorally, once daily for 7 days. Saliva and stool samples were obtained prior to drug administration, during administration (days 2, 4 and 7), and after withdrawal of the agents (days 9, 11, 14 and 21). The concentrations of levofloxacin and ofloxacin in the saliva and faecal samples, respectively, were assayed, and quantitative and qualitative microbiological analyses were performed. Oral administration of levofloxacin and ofloxacin led to low drug concentrations in the saliva, which corresponded with mild disturbances in the oral microflora. High drug levels were obtained in the intestinal tract, and both agents caused a selective reduction in the normal microflora, mainly directed towards aerobic Gram-negative bacteria. There was no significant difference between levofloxacin and ofloxacin, regarding ecological effects on the normal oral and intestinal microflora. From an ecological point of view, these agents acted favourably, since no major selection of resistant strains occurred in the normal microflora during administration.