A composition for pulmonary administration comprises a fluoroquinolone betaine, such as ciprofloxacin betaine, and an excipient. In one version, the particles have a mass median aerodynamic diameter from about 1 µm to about 5 µm, and the fluoroquinolone has a half life in the lungs of at least 1.5 hours. The composition is useful in treating an endobronchial infection, such as Pseudomonas aeruginosa, and is particularly useful in treating cystic fibrosis.
