The study aimed to determine the efficacy of a safe and well-Tolerated dose and regimen of tobramycin inhalation powder (TIP) on Pseudomonas aeruginosa sputum density in patients with bronchiectasis. This is a phase II, double-blind, randomised study in bronchiectasis patients aged 18 years with chronic P. aeruginosa infection. Patients were randomised 1:1:1 to either cohort A: Three capsules of TIP once daily (84 mg); cohort B: five capsules once daily (140 mg) or cohort C: four capsules twice daily (224 mg). Within each cohort, patients were further randomised 2:2:1 either to TIP continuously, TIP cyclically (alternating 28 days of TIP and placebo) or placebo for 16 weeks, respectively and were followed up for 8 weeks. Overall, 107 patients were randomised to cohorts A (n=34), B (n=36) and C (n=37). All three TIP doses significantly reduced the P. aeruginosa sputum density from baseline to day 29 versus placebo in a dosedependent manner (p 0.0001, each). A smaller proportion of patients in the continuous-TIP (34.1%) and cyclical-TIP (35.7%) groups experienced pulmonary exacerbations versus placebo (47.6%) and also required fewer anti-pseudomonal antibiotics (38.6% on continuous TIP and 42.9% on cyclical TIP) versus placebo (57.1%) although not statistically significant. Pulmonary exacerbation of bronchiectasis was the most frequent (37.4%) adverse event. Overall, TIP was well tolerated, however, 23.4% of the patients discontinued the study drug due to adverse events. Continuous-and cyclical-TIP regimens with all three doses were safe and effective in reducing the P. aeruginosa sputum density in patients with bronchiectasis and chronic P. aeruginosa infection.