Treatment of new Pseudomonas aeruginosa (Pa) infection in cystic fibrosis (CF) can postpone chronic infection. Aim of the study: compare 2 Pa eradication regimens in children with new Pa infection.

Methods: CF children (0-18 years) with a new isolation of Pa from the airway were randomized to tobramycin inhalation solution (TOBI® 2x300 mg for 28 days) (TIS) or inhaled colistimethate sodium (Colistineb® 2x2 mill U daily) plus oral ciprofloxacin (30mg/kg/day) for 3 months (CC). The primary outcome was eradication at end of treatment. Secondary outcome parameters were time to Pa relapse, total and Pa specific IgG, FEV1, BMI and Pa status.

Inclusion Criteria:

• diagnosis of CF (clinical signs consistent with CF and a sweat chloride > 60 mEq/l by quantitative pilocarpine iontophoresis and/or two CF causing mutations identified)
• age 0 to 18 years old at time of inclusion
• 'First' or 'new Pa infection' defined as 'first Pa isolation ever' or 'isolation of Pa from the airway (sputum, throat swab or BAL) after a Pa free interval of at least 6 months and documented with at least 3 negative cultures'.

Exclusion Criteria:

• chronic Pa infection defined according to the Leeds criteria[17]
• pulmonary exacerbation needing IV AB treatment at time of new Pa isolate
• Pa isolation at time of CF diagnosis
• patient already on an antipseudomonal antibiotic
• interval between positive culture and start of treatment > 4 weeks.