Pharmacokinetics of ciprofloxacin and effect of repeated dosage on salivary and fecal microflora.

The pharmacokinetics of ciprofloxacin was studied in 12 volunteers during a 5-day course of 500 mg of ciprofloxacin given orally twice a day. The effects on the microflora of saliva and feces were also examined. Serum and urine samples were assayed for ciprofloxacin microbiologically, and the salivary and fecal microflora were examined quantitatively after processing onto a series of selective media. Fecal samples were also investigated for the presence of Clostridium difficile and its cytotoxin. The MICs for new colonizing bacteria were examined in the salivary and fecal samples. There was no accumulation during the course of 5 days with peak serum concentrations identical (2.8 and 2.3 mg/liter) after the first and final doses, and the areas under the serum curves were similar (9.6 mg/liter). The serum half-life was 2.5 h on both days. The changes in the salivary flora were minor and affected only the neisseriae. In the fecal flora, the numbers of enterobacteria and enterococci decreased markedly, whereas the changes in anaerobic flora (anaerobic cocci, fusobacteria, and bacteroids) were not so pronounced. However, 14 days after the drug was discontinued, the salivary and fecal flora were normalized in all respects. No new colonization of ciprofloxacin-resistant bacteria for which MICs were above 1.0 mg/liter was observed. C. difficile or its cytotoxin was not detected.