This study is designed to provide data about the pharmacokinetics (PK), safety and tolerability of two continuous treatment regimes of tobramycin nebulized solution delivered via a 'soft mist' nebulizer in Cystic Fibrosis (CF) subjects. Each treatment period will last 8 weeks. Additionally the PK of patients with a normal forced expiratory flow in 1 second (FEV1) (FEV1≥80% predicted) will be compared to patients with an abnormal FEV1 (FEV1<80% predicted).

Inclusion Criteria:

• Male and female subjects aged ≥6 years at the time of screening, with an Informed Consent Form signed by patient and if appropriate by parent/legal guardians, prior to any study-related procedure.
• Confirmed diagnosis of CF by the presence of one or more clinical features of CF in addition to a quantitative pilocarpine iontophoresis sweat chloride test of >60 mEq/L; or identification of well-characterized disease-causing mutations in each CFTR gene; or an abnormal nasal transepithelial potential difference characteristic of CF.
• P aeruginosa must be present in sputum or deep throat swab (or bronchoalveolar lavage [BAL]) at the screening visit and within 6 months prior to screening.

Exclusion Criteria:

• History of sputum (or BAL) culture yielding Burkholderia cepacia (B cepacia) within 2 years prior to screening and/or sputum culture yielding B cepacia at screening.
• FEV1 <25% of normal predicted values for age, sex, and height based on Knudson criteria at screening.
• Hemoptysis of more than 60 cc at any time within 30 days prior to study drug administration.
• Known local or systemic hypersensitivity to aminoglycosides or inhaled antibiotics.
• GFR<60ml/min/1.73m2 calculated with the Formula by Schwartz, BUN 40 mg/dl or more, or an abnormal urinalysis defined as 2+ or greater proteinuria.
• History of tinnitus or pathologic audiometry
• diagnosis of Allergic bronchopulmonary aspergillosis (ABPA) at screening
• Initiation of treatment with macrolide antibiotics within 28 days prior to study drug administration (subjects may be taking macrolide antibiotics at the time of enrollment, but they must have initiated treatment at least 28 days prior to study drug administration).
• Use of loop diuretics within 7 days prior to study drug administration.

Other protocol-defined inclusion/exclusion criteria may apply