This study assessed time to recurrence of infection with Pseudomonas aeruginosa following treatment of the initial infection with tobramycin nebuliser solution. The safety profile of the initial tobramycin treatment was assessed during the first 3 months of the study and patients were followed until the end of the study, month 27.

This was a multi-center, open-label, two-arm, randomized study. All patients diagnosed with CF and who fulfilled the criteria for early infection with P. aeruginosa initially received tobramycin 300 mg twice a day for 28 days. At the end of the 28-day treatment period, patients who met the inclusion criteria and none of the additional exclusion criteria were randomized in a 1:1 ratio to either receive an additional 28 days of treatment with tobramycin 300 mg twice a day (56-day group) or to stop study medication (28-day group).

All randomized patients had regular study visits until a positive P. aeruginosa sample was obtained. Once P. aeruginosa had recurred, the patient entered a follow-up phase where minimal information was collected for 27 months. During the follow-up phase, patients were treated according to their physicians' discretion.

Patients who started treatment with tobramycin but were not randomized (i.e. due to a positive antibody test) and followed up during routine clinic visits. They were allowed to continue their 28-day treatment period and afterwards be treated according to their physicians' discretion.

Inclusion criteria:

• Male or female patients ≥ 6 months old

• Diagnosis of cystic fibrosis (CF) based upon the following historical criteria performed prior to study participation:

  1. confirmed sweat chloride > 60 mEq/L by quantitative pilocarpine iontophoresis (at least 2 tests), OR
  2. genotype with two identifiable mutations consistent with CF.

• First or early lower respiratory tract infection with Pseudomonas (P.) aeruginosa documented by either of the following:

  1. first infection defined by the first P. aeruginosa isolated from sputum or deep throat cough swab culture, OR
  2. P. aeruginosa from sputum or deep throat cough swab culture following at least 1 year of negative cultures (documented with at least 4 negative cultures during this year and no positive cultures) and no anti-pseudomonal treatment during this 1-year period, OR
  3. P. aeruginosa from sputum or deep throat cough swab culture following at least 2 years of negative cultures (documented with at least 2 negative cultures per year and no positive cultures) and no anti-pseudomonal treatment during this 2-year period.

• Written informed consent by the patient and/or parent/legal guardian according to local country regulations.

Exclusion criteria:

• History of aminoglycoside hypersensitivity or adverse reaction to inhaled aminoglycoside.
• Signs and symptoms of acute pulmonary disease, eg, pneumonia, pneumothorax.
• Administration of any investigational drug within 30 days prior to enrollment.
• Administration of loop diuretics within 7 days prior to study drug administration.
• Personal/family history of abnormal hearing, other than typical hearing loss associated with the aging process.
• Abnormal result from an audiology testing (defined as either a unilateral pure-tone audiometry test showing a threshold elevation > 20 decibels [dB] at any frequency across the frequency range 0.25-8 kHz or the absence of emission at the evoked otoacoustic emission test).
• Positive urine pregnancy test at Day 1 (Baseline) for all female patients who have reached menarche.
• Use of macrolide antibiotics as a maintenance therapy for 12 or more days during the 28 days prior to Baseline.
• Antibody titers ≥ 1000 for any of the 3 P. aeruginosa exoenzymes: Exotoxin A, alkaline protease, or elastase (status to be determined between Baseline and Day 28).

From Baseline to the end of the study (Month 27)

Adverse events (AE) were recorded for the safety population which included all patients who received at least 1 dose of study medication. For patients withdrawn from the study who continued in the follow-up phase, all AEs were recorded until Month 3. After Month 3, only AEs recorded related to study drug were recorded.