Effects of norfloxacin on the faecal flora in patients with complicated urinary tract infections.

The effects on the long-term use of norfloxacin, a fluorinated 4-quinolone, on the intestinal flora (both aerobic and anaerobic), were evaluated in patients suffering from recurrent complicated urinary tract infections. Eight patients received norfloxacin 400 mg b.i.d. for three months, and 11 patients received 400 mg b.i.d. for one month, and then 400 mg as an evening dose for two months. The concentration of Enterobacteriaceae, staphylococci, Streptococcus faecalis, and yeasts in stool specimens, together with the norfloxacin concentration were measured every month. The beta-aspartyl-glycine test was carried out at the same time. No urinary tract infections, either of exogenous (Pseudomonas spp.) or endogenous origin could be diagnosed during norfloxacin therapy. At both dosages of norfloxacin the faecal samples were free of Enterobacteriaceae due to low minimal bactericidal concentrations and high faecal drug concentrations. The suppressive effect was selective in that the anaerobic flora was left intact. A suppression of the aerobic intestinal flora could lead to an important reduction of recurrent infections of the urinary tract in these patients.