Aztreonam for Inhalation (AI) in Patients With Cystic Fibrosis & P. Aeruginosa Infection

Inclusion Criteria: * Written informed consent prior to the performance of any study related procedures. * 13 years of age and above. * Documented sweat chloride ≥ 60 mEq/L by quantitative pilocarpine iontophoresis test (QPIT) or homozygosity for ΔF508 genetic mutation or heterozygosity for two well characterized mutations. * Ability to perform pulmonary function tests. * FEV1 ≥ 40% predicted at Visit 1 (Screening). * SaO2 ≥ 90% at Visit 1 (Screening). * P. aeruginosa present in sputum at Visit 1 (Screening). * Ability to expectorate sputum on a daily basis. Exclusion Criteria: * Administration of any antibiotic with antipseudomonal activity by any route within 56 days prior to Visit 1 (Screening). * Administration of any investigational drug or device within 28 days of Visit 1 (Screening) and within 6 half-lives of the investigational drug. * Oral corticosteroids in doses exceeding 10 mg per day or 20 mg every other day. * History of sputum culture or throat swab culture yielding B. cepacia in the previous two years. * Current daily continuous oxygen supplementation or requirement for more than 2 L/min at night. * Known local or systemic hypersensitivity to monobactam antibiotics. * Changes in antimicrobial, bronchodilator, anti-inflammatory or corticosteroid medications within 7 days prior to Visit 1 (Screening). * Changes in physiotherapy technique or schedule within 7 days prior to Visit 1 (Screening). * History of lung transplantation. * A chest radiograph at Visit 1 (Screening) or within the previous 90 days of Screening, with abnormalities indicating a significant acute finding (eg, lobar infiltrate and atelectasis, pneumothorax, or pleural effusion). * Abnormal renal or hepatic function or serum chemistry at Visit 1 (Screening): * AST, ALT \> 2.5 times upper limit of normal range. * Creatinine \> 1.5 times upper limit of normal range. * Positive pregnancy test. All women of childbearing potential will be tested. * Female of childbearing potential who is lactating or is not practicing acceptable method of birth control (eg, hormonal or barrier methods, or IUD). * Findings at Visit 1 (Screening) that, in the investigator's opinion, would compromise the safety of the patient or the quality of the study data.