Safety and Efficacy Study of Aztreonam for Inhalation Solution (AZLI) in Cystic Fibrosis Patients With P. Aeruginosa

Inclusion Criteria: * CF as diagnosed by: 1. Documented sweat chloride greater than or equal to 60 mEq/L by quantitative pilocarpine iontophoresis test; or 2. Two well-characterized genetic mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene; or 3. Abnormal nasal potential difference with accompanying symptoms characteristic of CF. * PA present in expectorated sputum or throat swab culture at Screening. * Participants must have received three or more courses of TIS within the previous 12 months. * Participants on chronic azithromycin must have had no change in regimen in the previous 3 months and must have had a need for TIS and/or additional antipseudomonal therapy since initiation of azithromycin. * Forced expiratory volume in 1 second (FEV1) between (and including) 25% and 75% predicted at Screening. * Ability to perform reproducible pulmonary function tests. * Arterial oxygen saturation (SaO2) greater than or equal to 90% on room air at Screening. Exclusion Criteria: * Current use of oral corticosteroids in doses exceeding the equivalent of 10 mg prednisone a day or 20 mg prednisone every other day. * History of sputum or throat culture swab yielding Burkholderia cepacia in the past 2 years. * History of daily continuous oxygen supplementation or requirement for more than 2 liters/minute at night. * Administration of any investigational drug or device within 28 days of Screening (Visit 1) or within 6 half-lives of the investigational drug (whichever was longer). * Known local or systemic hypersensitivity to monobactam antibiotics. * Inability to tolerate inhalation of a short acting Beta-2 agonist. * Changes in antimicrobial, bronchodilator, anti-inflammatory, or corticosteroid medications within 7 days before Screening or between Screening and the next visit. * Changes in physiotherapy technique or schedule within 7 days before Screening or between Screening and the next visit. * History of lung transplantation. * A chest X-ray indicating abnormal findings at Screening or within the previous 90 days. * Abnormal renal or hepatic function or serum chemistry at Screening (aspartate aminotransferase \[AST\], alanine aminotransferase \[ALT\] greater than 5 times the upper limit of normal range; Creatinine greater than 2 times the upper limit of normal range). * Positive pregnancy test at Screening. * Female of childbearing potential who was lactating or in the opinion of the investigator was not practicing acceptable birth control. * Any serious or active medical or psychiatric illness, which in the opinion of the investigator would have interfered with participant treatment, assessment, or compliance with the protocol.