• Time to next airway-colonization (re-colonization) with Pseudomonas aeruginosa [ Time Frame: up to 5 years ] [ Designated as safety issue: No ]
  

• Clinical condition of the patients (height, weight and lung function) [ Time Frame: up to 5 years ] [ Designated as safety issue: Yes ]
  
• Bacteriological examination of Pseudomonas aeruginosa (phenotype, resistance) [ Time Frame: 5 years ] [ Designated as safety issue: No ]
  
• Genotyping of Pseudomonas aeruginosa using Pulsed Field Gel Electrophoresis (re-infection caused by identical or new strain) [ Time Frame: 5 years ] [ Designated as safety issue: No ]
  
• Specific, precipitating pseudomonas-antibodies (establishment of chronic infection) [ Time Frame: 5 years ] [ Designated as safety issue: No ]
  

Cystic Fibrosis is the most common genetic, inherited, deadly disease in caucasians. The disease is characterized by recurrent airway-infections caused by Pseudomonas aeruginosa, ultimately leading to chronic airway-infection, which is the main cause of the increased morbidity and mortality seen in this disease.

P. aeruginosa has the ability to change to mucoid phenotype - producing alginate and growing in biofilm, which protects the microorganisms from antibiotics and leukocytes. The change in phenotype is seen as chronic infection is established and eradication becomes impossible. Treatment with long-term, low-dose azithromycin in chronically infected CF-patients can improve the clinical condition of the patients. The exact mechanism for this is not known, but is possibly a combination of anti-inflammatory effects and the ability of azithromycin to inhibit alginate-production. Inhibition of biofilm-formation leaves the bacteria more susceptible to the actions of antibiotics and leukocytes.

Prior to establishment of chronic infection, recurrent, intermittent colonization of the airways with non-mucoid P. aeruginosa is seen. Intermittent infections can be treated using a combination of antibiotics, thereby postponing the next episode of airway-infection with P. aeruginosa.

The purpose of this study is to clarify wether supplementary azithromycin in the treatment of intermittent pseudomonas-infection in CF-patients can lead to further postponement of next pseudomonas-colonization and maybe prevent development of chronic infection. This is done in a randomised, double-blinded, placebo-controlled multicentre study.

2 treatments will be compared:

1. Inhaled colistin and oral ciprofloxacin in combination with oral azithromycin
2. Inhaled colistin and oral ciprofloxacin in combination with oral placebo.

The treatment will be given for 3 weeks, and the primary end-point is the time until next colonization with P. aeruginosa in the airways of the patients, comparing the 2 treatment-groups.