Inclusion Criteria:

• Compliance with studies CP-AI-005 or CP-AI-007 by taking at least 50% of expected study medication.
• Completion of CP-AI-005 or CP-AI-007 within the previous 60 days or was withdrawn due to need for antipseudomonal antibiotics or for an AE unrelated to study medication tolerance.
• Ability to provide written informed consent/assent prior to initiation of study-related procedures.
• Ability to perform reproducible pulmonary function tests.

Exclusion Criteria:

• Use of any investigational medication or device between the last visit of CP-AI-005/007 and Visit 1 of CP-AI-006.
• Concurrent participation in a study of another investigational drug or device.
• Current use of oral corticosteroids in doses exceeding the equivalent of 10 mg prednisone/day or 20 mg prednisone every other day.
• History of sputum or throat swab culture yielding Burkholderia cepacia in the previous 2 years.
• History of daily continuous oxygen supplementation or requirement for more than 2 liters/minute at night.
• Inability to tolerate study medication in study CP-AI-005/007.
• Known local or systemic hypersensitivity to aztreonam.
• Inability to tolerate inhalation of a short acting beta-2 agonist.
• Abnormal renal or hepatic function based on results of most recent test.
• Female of child-bearing potential who is pregnant, lactating, or is not (in the opinion of the investigator) practicing an acceptable method of birth control.
• 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.