This study assesses the aerosol delivery characteristics (measured by nebulization time, serum and sputum tobramycin pharmacokinetic parameters) and safety of tobramycin administered for inhalation by PARI eFlow rapid electronic nebulizer (no compressor) vs. PARI LC PLUS Jet Nebulizer (with compressor) in subjects with cystic fibrosis.

Inclusion Criteria:

• Male and female subjects aged 6 years or over at the time of screening,
• Chronically colonized with Pseudomonas aeruginosa.
• Diagnosis of cystic fibrosis (CF)
• Ability to expectorate sputum samples on command.
• Ability to tolerate a 1-week washout interval with no inhaled tobramycin or other aminoglycoside treatment.
• Clinically stable in the opinion of the investigator.

Exclusion Criteria:

• Inhaled or intravenous aminoglycosides within 7 days before study drug administration.
• Any investigational drug within 2 weeks before screening.
• Loop diuretics within 7 days before study drug administration.
• Current use of inhaled tobramycin delivered by the PARI LC PLUS jet nebulizer without washout period of at least 1 week before entering the study.
• Women who are, or plan to become, pregnant during the course of the study.
• Serum creatinine or blood urea (BU) above the upper limit of normal for sex and age, or an abnormal urine analysis
• Known local or systemic hypersensitivity to aminoglycosides.

Other protocol defined inclusion/exclusion criteria may apply.