Pharmacokinetics and pharmacodynamics of ciprofloxacin in cystic fibrosis patients

The pharmacokinetics and blister fluid penetration of oral ciprofloxacin were compared in 11 cystic fibrosis (CF) patients who had sputum colonization but were asymptomatic and in 12 healthy volunteers after a single dose (500 mg) and at steady state (500 mg every 8 h). The antibacterial effect of ciprofloxacin therapy was also evaluated by bacterial counts of colonizing pathogens in the respiratory secretions of CF patients. The CF patients were 15.9% lighter in weight than the controls (P less than 0.05). After a single dose, the elimination half-life of ciprofloxacin was decreased by a third in the CF patients as compared with the controls (2.62 versus 3.93 h, respectively; P less than 0.01). This was the result of a diminished apparent volume of distribution in CF subjects. Interestingly, we observed no statistically significant difference in total apparent and renal clearances between the groups. Suction-induced blister fluid penetration was not different between CF patients and healthy volunteers. In CF patients, ciprofloxacin exhibited levels in respiratory secretions above the reported MIC for Pseudomonas aeruginosa: 1.36 and 1.86 micrograms/ml at 2 h after a single dose and at steady state, respectively. An important fall (mean, 3.9 log10/ml) in the log titer in 10 patients with P. aeruginosa in their respiratory secretions was observed after 5 days of treatment. However, this improvement was short-lived; the secondary increase in bacterial counts observed in five patients and the development of five resistant strains were causes for concern. The pharmacokinetic results presented here showed that ciprofloxacin should be administered every 8 or even every 6 h in CF patients.