Norfloxacin: activity against urinary tract pathogens and factors influencing the emergence of resistance.

The activity of norfloxacin was investigated in vitro in conventional minimum inhibitory concentration tests, by continuous turbidimetry and in a mechanical model simulating the hydrokinetic conditions that exist in the treatment of bacterial cystitis. The high activity of norfloxacin against virtually all bacterial pathogens isolated from infected urine was confirmed. However, in urine agar (pH 6 X 5) and in DST agar adjusted to pH 5 X 5, the activity was substantially reduced. Turbidimetric experiments indicated that increases in resistance to norfloxacin could be induced easily by sequential subculture, but results obtained in the bladder model, where conditions of exposure more closely resemble those that exist during the treatment of infection, suggest that such resistance is unlikely to arise commonly during treatment.