This is a pilot study of inhaled antibiotic regimens is a pilot study examining clinical and laboratory endpoints of patients on inhaled antibiotic treatments. We hypothesize that alternation therapy utilizing Cayston and Tobi will inhibit antibiotic resistance and that alternation therapy will result in a decreased incidence of antibiotic resistance to Cystic Fibrosis (CF) microbial isolates. The long term strategic goal is to develop a model biometric system for selecting a patient's optimal inhaled antibiotic regimen by utilizing clinical and microbiological parameters.

Inclusion Criteria:

• > or = to 6 years of age
• Documentation of Cf diagnosis
• History of PA present in sputum, on a least one occasion, during the 12 months prior to Visit 1.
• Currently on inhaled antibiotic regiment
• Must be able to provide written informed consent or assent prior to any study related procedures
• Ability to expectorate sputum
• Ability ro perform reproducible pulmonary function test

Exclusion Criteria:

• Administration of any IV or oral antipseudomonal antibiotic within 28 days prior to Visit 1
• Any serious or active medical or psychiatric illness, which in the opinion of the investigator, woud interfere with participant treatment, assessment, or compliance with the protocol
• Current enrollment in an interventional clinical trial

Primary care clinic