The effect of quinolone antibacterials on the gastrointestinal flora compared with that of other antibacterials.

Although there is limited information on some of the newer quinolones it is likely that all such agents have a similar effect on the faecal flora. Ciprofloxacin seems to be best studied, and typical changes include regular and complete suppression of the enterobacteria and a slight diminution of enterococci. Total counts of anaerobic flora remain virtually unchanged, although small reductions have been noted in some studies for bacteroids, anaerobic cocci, fusobacteria and anaerobic non-sporing Gram-positive bacilli. Overgrowth of yeasts was not seen except when administration was prolonged. The results so far suggest that the newer quinolones will have a useful role in selective gut decontamination, the prevention of reinfection of the urinary tract, and the treatment of intestinal infection. Such early clinical results as have been published confirm this view. Of the other antibacterial agents discussed only some recent cephalosporins (cefotaxime, ceftazidime), aztreonam, cotrimoxazole and aminoglycosides have effects on the faecal flora similar to those of the newer quinolones. The remaining agents either have little or no effect or produce changes, such as a marked reduction in anaerobic flora, which are generally considered to be undesirable.