Study was terminated early by sponsor due to the challenges and risks introduced by Coronavirus disease 2019 (COVID-19) pandemic.

The primary objective of this study is to evaluate the safety and efficacy of a 14-day course versus a 28-day course of aztreonam for inhalation solution (AZLI) in pediatric participants with new onset Pseudomonas aeruginosa respiratory tract infection or colonization.

Key Inclusion Criteria:

• Diagnosis of cystic fibrosis (CF) as determined by the 2008 CF Consensus Conference criteria: Sweat chloride level ≥ 60 milliequivalents per liter (mEq/L) by quantitative pilocarpine iontophoresis; or a genotype with 2 identifiable mutations consistent with CF; or an abnormal nasal transepithelial potential difference (NPD), and 1 or more clinical features consistent with CF
• Documented new onset of positive respiratory tract culture for PA within 30 days of screening defined as either first lifetime documented PA-positive culture, or PA recovered after at least a 2-year history of PA-negative respiratory cultures (at least 2 cultures per year)
• Forced expiratory volume in one second (FEV1) ≥ 80% predicted (for subjects ≥ 6 years of age who can reliably perform spirometry assessments)
• Clinically stable with no evidence of acute significant respiratory symptoms that would require administration of intravenous (IV) antipseudomonal antibiotics, oxygen supplementation, or hospitalization

Key Exclusion Criteria:

• Use of IV or inhaled antipseudomonal antibiotics within 2 years of screening
• Use of oral antipseudomonal antibiotics for a respiratory event within 30 days of study entry (screening visit)
• History of intolerance to inhaled short acting β2 agonists
• History of lung transplantation
• Current requirement for daily continuous oxygen supplementation or requirement of more than 2 L/minute at night
• Hospitalization for a respiratory event within 30 days prior to screening
• Changes in bronchodilator, corticosteroid, dornase alfa, or hypertonic saline medications within 7 days prior to screening.
• Significant changes (per investigators discretion) in physiotherapy technique or schedule within 7 days prior to screening
• Abnormal renal or hepatic function results at most recent test within the previous 12 months, defined as Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) > 5 times upper limit of normal (ULN), or Serum creatinine > 2 times ULN for age
• Presence of a condition or abnormality that would compromise the subject's safety or the quality of the study data, in the opinion of the Investigator
• Known hypersensitivity to aztreonam, its metabolites, or formulation excipients in AZLI
• Respiratory cultures performed within 24 months prior to screening that are positive for ANY Burkholderia spp. or Non-tuberculous mycobacteria (NTM)

Note: Other protocol defined Inclusion/Exclusion criteria may apply

Qualified external researchers may request IPD for this study after study completion. For more information, please visit our website at https://www.gileadclinicaltrials.com/transparency-policy/

18 months after study completion

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After conclusion of the study and without prior written approval from Gilead, investigators in this study may communicate, orally present, or publish in scientific journals or other media only after the following conditions have been met:

• The results of the study in their entirety have been publicly disclosed by or with the consent of Gilead in an abstract, manuscript, or presentation form; or
• The study has been completed at all study sites for at least 2 years