Effects of daily oral administration of rifaximin and neomycin on faecal aerobic flora in rats.

The aim of this study was to compare the influence of rifaximin and neomycin on faecal flora in rats. The study was performed on 18 Wistar rats (three groups of six male animals). Group 1 received rifaximin (50 mg kg(-1)/day), group 2, neomycin (50 mg kg(-1)/day) and group 3 was used as control. Drugs were administered orally, once daily for 3 days. Faecal specimens, collected from each rat on day 3, were cultured for the quantitative and qualitative determination of aerobic microorganisms. Rifaximin treatment produced a marked reduction in the number of total aerobic bacteria and Salmonellae; neomycin caused reduction in Salmonellae, but did not cause statistically significant changes in total aerobic bacterial count. The binding of neomycin with faeces could explain this limited activity, which does not correlate with the in vitro susceptibility of the organism affected. These results confirm that rifaximin is suitable for topical treatment to reduce selected bacterial load in the gut intestines.