Background Inhaled antibiotics have achieved or stabilised the clinical condition of patients with cystic fibrosis (CF) and chronic Pseudomonas aeruginosa infection. We aimed to determine the effectiveness of aztreonam lysine inhaled solution (AZLI) in patients with CF and chronic P. aeruginosa infection.

Methods A retrospective observational study was conducted on patients with CF and chronic P. aeruginosa infection who received AZLI between July 2012 and September 2018 inclusive in three Spanish hospitals in a routine clinical practice setting. The primary endpoint was the absolute change in the percentage of predicted forced expiratory volume in 1 second (FEV₁) compared with the previous 12 months, at the start of AZLI treatment and 12 months after starting the drug. Other variables analysed were exacerbations, hospitalisations, type and route of antibiotics prescribed, weight and body mass index (BMI) and adverse drug reactions.

Results In a cohort of 52 patients, AZLI treatment led to stabilisation of FEV₁, changing from a mean (SD) value of 55.60 (21.3)% at the start of treatment to 56.8 (20.4)% after 12 months of treatment (p=0.5296) in patients who had not previously received the drug. In addition, it significantly reduced exacerbations from a median (P25; P75) of 2.0 (1.0; 3.0) in the 12 months prior to AZLI to 1.0 (1.0; 2.0) in the 12 months after treatment initiation (p=0.0350). AZLI also reduced the need for other antibiotics and prevented a decrease in BMI, with an adequate safety profile.

Conclusions AZLI achieved stabilisation of lung function measured by FEV₁ in patients with CF and chronic P. aeruginosa infection, along with an adequate safety profile.