Development of Azithromycin-Loaded Nanostructured Lipid Carriers for Nebulized Delivery in Cystic Fibrosis-Associated Pseudomonas aeruginosa Infections

Cystic fibrosis (CF) is frequently complicated by persistent pulmonary infection with Pseudomonas aeruginosa , highlighting the need for effective local antibiotic delivery. This study developed azithromycin-loaded nanostructured lipid carriers (AZT-NLCs) as an inhalable nanocarrier designed to enhance local pulmonary delivery of azithromycin. AZT-NLCs were systematically optimized using a Box–Behnken design and evaluated for physicochemical properties, drug release, antibacterial and antibiofilm activities, aerosol performance, and airway epithelial compatibility. The optimized AZT-NLCs had a particle size of approximately 369 nm, polydispersity index of 0.28, zeta potential of −29.52 mV, and encapsulation efficiency of 89.99%. AZT-NLCs provided two-fold lower minimum inhibitory concentration against P. aeruginosa , decreasing from 31.25 µg/mL for free azithromycin to 15.63 µg/mL. Aerosol characterization using a Next Generation Impactor demonstrated favorable pulmonary delivery characteristics, with a mass median aerodynamic diameter of 3.39 ± 0.10 µm and a fine particle fraction (<5 µm) of 63.32 ± 2.21%. Importantly, AZT-NLCs were taken up by airway epithelial cells without disrupting barrier integrity in air–liquid interface models and exhibited limited transepithelial transport of NLC-associated fluorescence (0.43 ± 0.01%), indicating minimal translocation across the epithelial barrier. Collectively, these findings integrate nanocarrier optimization with aerosol and biologically relevant performance assessments, supporting AZT-NLCs as a promising inhalable platform for local azithromycin delivery and providing a foundation for further translational investigation in CF-associated P. aeruginosa respiratory infections.