Patients with cystic fibrosis (CF) suffer from chronic infections of the lower respiratory tract that can be caused by one or multiple bacteria, including Pseudomonas aeruginosa, which has been particularly problematic to eradicate and been implicated as the major cause of morbidity and mortality in CF patients. Aerosol delivery of antibiotics directly to the lung increases the local concentrations of antibiotic at the site of infection resulting in improved antimicrobial effects compared to systemic administration. Bacterial resistance to current aerosol antibiotic treatments indicate a need for improved therapies to treat CF patients with pulmonary infections caused by multi-drug resistant Pseudomonas aeruginosa and other bacteria. High concentrations of MP-376 delivered directly to the lung are projected to have antimicrobial effects on even the most resistant organisms and reduce the emergence of resistant bacteria.