Effect of oral ciprofloxacin on the faecal flora of healthy volunteers.

The effect of oral ciprofloxacin on the intestinal flora was investigated in six male volunteers aged between 21 and 54 years. Faecal specimens were cultured quantitatively for aerobic and anaerobic micro-organisms before, during and after a five day course of ciprofloxacin. Ciprofloxacin resulted in a significant reduction in aerobic flora in all volunteers and colonisation with resistant coagulase-negative staphylococci or corynebacteria in two volunteers. The total anaerobic flora counts were significantly reduced in only one volunteer. Neither Clostridium difficile nor its toxin was detected and there was no significant colonisation with Pseudomonas spp. or yeasts; no ciprofloxacin-resistant gram-negative bacilli were detected. Peak serum levels on days 1 and 5 of 1.6-4.3 mg/l (mean 2.7) were achieved after 30-90 min and urine recovery over the five days was 27.1-44.6%.