Comparative effects of the immediate and the extended release formulations of ciprofloxacin on normal human intestinal microflora.

Ciprofloxacin is a well-known fluoroquinolone, active in vitro against most Gram-negative and Gram-positive bacteria. The purpose of the present study was to evaluate the ecological effects of an orally administered extended-release formulation of ciprofloxacin in comparison with an immediate-release formulation of ciprofloxacin on the normal human intestinal microflora. Thirty-six healthy female subjects were included in the study. the extended-release formulation of ciprofloxacin was given as 500 mg once daily and the immediate-release formulation as 250 mg twice daily. The treatment period was 3 days. the microbiological investigation was blinded with respect to treatment. Mean fecal concentration in the volunteers receiving the extended-release formulation ciprofloxacin was 453 mg/kg and in the immediate-release formulation ciprofloxacin volunteers, the mean fecal concentration was 392 mg/kg. The numbers of Escherichia coli were significantly suppressed while the enterococci decreased moderately in both treatment groups. No toxigenic Clostridium difficile strains were found. No major differences were observed between the two studied formulations on the normal human intestinal microflora.