title: Resistance to ciprofloxacin of respiratory pathogens in patients with cystic fibrosis.
abstract: OBJECTIVE
  To determine the incidence of resistance to ciprofloxacin in respiratory pathogens isolated from patients with cystic fibrosis (CF) compared with that of isolates from patients without CF. The hypothesis was that repeated exposure of these respiratory pathogens to ciprofloxacin would reduce their sensitivity.
  
  
  METHODS
  Isolates of Pseudomonas aeruginosa and Staphylococcus aureus were obtained prospectively from sputa of patients with CF, as part of their routine care. The sensitivities of these isolates to ciprofloxacin were determined by standard agar dilution techniques.
  
  
  METHODS
  The study was carried out in patients who attended the outpatient clinic or were treated as inpatients of a tertiary referral hospital. Sputa were obtained from 71 patients with CF (age range, 2-31 years) and isolates of P. aeruginosa and S. aureus were compared with those from 54 hospital patients who did not have CF.
  
  
  METHODS
  Sensitivities to ciprofloxacin, expressed as the minimal concentrations required to inhibit growth of the organisms (MIC), were used to make comparisons between different isolates and the same isolates within patients at different times.
  
  
  RESULTS
  A higher incidence of ciprofloxacin resistance was displayed by isolates of P. aeruginosa from CF patients who had been previously prescribed ciprofloxacin (MIC50 of 2.0 mg/L and 4.0 mg/L for mucoid and non-mucoid strains respectively). The MIC of individual organisms tended to rise after a course of ciprofloxacin had been given to their host. A much lower incidence of resistance was displayed by isolates of P. aeruginosa from patients without CF (MIC50, 0.25 mg/L). Similarly, S. aureus isolates from patients with CF exhibited greater resistance to ciprofloxacin (MIC50, 32 mg/L) than isolates from other patients (MIC50, 0.75 mg/L).
  
  
  CONCLUSIONS
  The resistance of P. aeruginosa appears to be related to ciprofloxacin exposure, so further development of resistance may be diminished by restricting the frequency of ciprofloxacin administration to individual patients.
authors.affiliation: Department of Pharmacology, University of Sydney, NSW.
authors.forename: R E
authors.initials: RE
authors.lastname: Dostal
authors.forename: J P
authors.initials: JP
authors.lastname: Seale
authors.forename: B J
authors.initials: BJ
authors.lastname: Yan
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D002939:Ciprofloxacin / Q000494:pharmacology* / Q000627:therapeutic use; D003550:Cystic Fibrosis / Q000382:microbiology*; D004305:Dose-Response Relationship, Drug; D004352:Drug Resistance, Microbial; D006801:Humans; D008826:Microbial Sensitivity Tests; D011550:Pseudomonas aeruginosa / Q000187:drug effects*; D012137:Respiratory System / Q000382:microbiology*; D013183:Sputum / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects*
chemical_list: D002939:Ciprofloxacin