Inclusion Criteria:

1. Patients ≥ 6 years of age.

2. Documentation of CF diagnosis as evidenced by one or more clinical features consistent with the CF phenotype and one or more of the following criteria:

   i. Sweat chloride ≥ 60 mEq/L by quantitative pilocarpine iontophoresis test (QPIT);

   ii. Two well-characterized mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene; or

   iii. Abnormal nasal potential difference.

3. PA present in expectorated sputum or throat swab culture at Visit 1 OR documented PA in 2 expectorated sputum or throat swab cultures within the 12 months prior to Visit 1. (One of the previous PA positive cultures must be no more than 3 months prior to Visit 1.)
4. FEV1 > 75% predicted at Visit 1.

5. Patient must exhibit two or more of the following chronic and/or intermittent CF symptoms, for a minimum of 28 days prior to randomization and with no worsening of symptoms within 7 days prior to randomization:

   i. Chest congestion

   ii. Daily cough

   iii. Productive cough

   iv. Wheezing

   v. Trouble breathing

   vi. Nocturnal wakening due to coughing

6. Patients (and parent/guardian as required) must be able to provide written informed consent/assent prior to any study related procedures.
7. Females of childbearing potential must have a negative urine pregnancy test at Visit 1.
8. Ability to perform reproducible pulmonary function tests.
9. In the opinion of the Investigator, the patient does not require immediate antipseudomonal antibiotic intervention to treat an impending exacerbation, and the patient's condition is stable enough to enroll in the study.

Exclusion Criteria:

1. Administration of any investigational drug or device within 28 days prior to Visit 1 or within 6 half-lives of the investigational drug (whichever is longer).
2. Administration of any IV, oral, or inhaled antipseudomonal antibiotic within 28 days prior to Visit 1.
3. Known local or systemic hypersensitivity to monobactam antibiotics.
4. Inability to tolerate short-acting bronchodilator use at least three times daily.
5. Changes in or initiation of chronic azithromycin treatment within 28 days prior to Visit 1.
6. Changes in or initiation of chronic hypertonic saline treatment within 28 days prior to Visit 1.
7. Changes in or initiation of dornase alpha within 28 days prior to Visit 1.
8. Changes in antimicrobial, bronchodilator (BD), or corticosteroid medications within 7 days prior to Visit 1.
9. Changes in physiotherapy technique or schedule within 7 days prior to Visit 1.
10. History of lung transplantation.
11. History of participation (enrollment) in any prior clinical trials with AZLI.
12. A chest radiograph at Visit 1 (or within the previous 180 days of Visit 1), with abnormalities indicating a significant acute finding (e.g., lobar infiltrate and atelectasis, pneumothorax, or pleural effusion). A chest radiograph obtained and interpreted between Visits 1 and 2 is also acceptable for determining eligibility.
13. Positive urine pregnancy test at Visit 1; all women of childbearing potential will be tested.
14. Females of childbearing potential who are lactating or are not (in the opinion of the investigator) practicing an acceptable method of birth control; female patients who utilize hormonal contraceptives as their birth control method must have used the same method for at least 3 months before study dosing.
15. Patient is being assessed at Visit 1 by the investigator for an acute change in respiratory symptoms.
16. Any serious or active medical or psychiatric illness, which in the opinion of the investigator, would interfere with patient treatment, assessment, or compliance with the protocol.