Safety of Combined Intravenous Antibiotic and Bacteriophage Therapy in Adults With Cystic Fibrosis and Antibiotic-Resistant Lung Infections

Inclusion Criteria: * Age ≥ 18 years. * Confirmed diagnosis of cystic fibrosis. * Sputum culture within 24 months and at screening showing at least one of the following: Pseudomonas aeruginosa, Klebsiella spp., Stenotrophomonas maltophilia, Escherichia coli, Staphylococcus aureus, or Achromobacter xylosoxidans. * Percent predicted FEV₁ ≥ 40% (GLI). * If ppFEV₁ \> 40%, must have ≥ 1 pulmonary exacerbation per year requiring IV antibiotics or radiographic evidence of severe disease. * Prior successful home IV antibiotic therapy within 5 years (may be waived by investigator). * Available phage cocktail with lytic activity against the participant's pathogen. Oxygen saturation \> 88% on room air after rest. Able to provide written informed consent. Exclusion Criteria: * Untreated or uncontrolled mycobacterial or fungal airway infection. * History of Clostridioides difficile without a negative test within 3 months. Concerning exotoxin, virulence, or resistance genes in the bacterial isolate (per investigator). * Mixed-species bacterial infection at screening. * Participation in another interventional trial within 30 days. * Allergy or hypersensitivity to study materials. * Pregnancy, planned pregnancy, or breastfeeding. * Any condition or abnormality that, in the investigator's judgment, makes participation unsafe or may interfere with study assessments.