This was a randomized multi-center clinical trial to compare the microbiological efficacy, clinical efficacy, and safety of using standard versus biofilm susceptibility testing of P. aeruginosa sputum isolates to guide antibiotic selection for treatment of airway infection in clinically stable patients with CF.

Patients were screened to determine eligibility and to obtain a sputum culture. Eligible patients were randomized to either the standard or biofilm study arm. Antibiotic selection was performed centrally according to a standard algorithm using the susceptibility test results of the assigned study arm. On Day 0, patients were started on a 14-day course of two antibiotics as selected per protocol. Antibiotics were administered intravenously (IV) and/or orally. A follow-up phone call or visit occurred on Day 7. An end of treatment visit was conducted after completion of antibiotic therapy. A total of 39 patients were randomized. Many screened patients were ineligible for randomization based on microbiology results.

Inclusion Criteria:

• Diagnosis of CF based on the following: sweat chloride > 60 mEq/L (by quantitative pilocarpine iontophoresis), or genotype with 2 identifiable mutations consistent with CF; and one or more clinical features consistent with CF.
• Age ≥ 14 years (changed from ≥ 18 years by protocol amendment).
• Able to expectorate sputum at screening.
• History of persistent positivity for P. aeruginosa on respiratory culture (at least three positive oropharyngeal (OP), sputum and/or bronchoscopy cultures in the 24 months prior to screening).
• Able to reproducibly perform pulmonary function testing.
• Clinically stable at screening, with no evidence of pulmonary exacerbation.
• Written informed consent provided.

Exclusion Criteria:

• Sputum culture negative for P. aeruginosa or density less than 10E5 CFU/gm at screening.
• Sputum culture positive for B. cepacia at screening.
• Presence of P. aeruginosa in sputum with off-scale resistance to all antibiotics by either method of susceptibility testing at screening. (changed from multiply-resistant P. aeruginosa by protocol amendment)
• History of B. cepacia positive respiratory culture within 24 months prior to screening.
• Hospitalization or treatment for a pulmonary exacerbation within 2 months prior to screening.
• Administration of parenteral anti-pseudomonal antibiotics within 2 months prior to screening.
• Treatment with oral or inhaled anti-pseudomonal antibiotics, or azithromycin or other macrolides within 14 days prior to screening.
• History of allergy (urticarial rash, diffuse erythroderma, serum sickness) to more than two groups of antibiotics (aminoglycosides, penicillins, cephalosporins, monobactams, macrolides, or quinolones) that are a therapeutic option.
• History of anaphylaxis or other life threatening complication to any antibiotic in the six groups that are a therapeutic option.
• History of abnormal renal function (serum creatinine > 1.5 x upper limit of normal) within one year of enrollment.
• History of abnormal liver function tests (> 2.5 x upper limit of normal) within one year of enrollment.
• Clinically documented hearing loss that precludes treatment with aminoglycosides.
• Post lung transplantation.
• Positive pregnancy test or female who is lactating or is not practicing an acceptable method of birth control.
• Presence of a condition or abnormality that in the opinion of an investigator would compromise the safety of the patient or the quality of the data.
• Administration of any investigational agent within 30 days prior to screening.