Rationale: Patient registries have the potential to collect and analyze high-quality postauthorization data on new medicines.

Objectives: We used cystic fibrosis (CF) registry data to assess outcomes after the initiation of ivacaftor, a CF transmembrane conductance regulator (CFTR) potentiator approved for the treatment of CF with a defective gating CFTR mutation.

Methods: Longitudinal trends were examined using mixed-effects regression analysis in 80 ivacaftor-treated patients with CF aged 6 to 56 years registered with the CF Registry of Ireland with at least 36 months of before and after commencement data. The effects of ivacaftor treatment on forced expiratory volume in 1 second (FEV₁) % predicted, body mass index (BMI), hospitalization for pulmonary exacerbation, and oral and intravenous antibiotic use were assessed.

Results: In the 36 months after ivacaftor initiation, FEV₁% predicted improved by 2.26% per annum (95% confidence interval [CI], 0.2 to 4.3) for patients aged younger than 12 years, remained unchanged for 12- to younger than 18-year-olds (95% CI, −1.9 to 2.9), and declined in adults by 1.74% per annum (95% CI, −3.1 to −0.4). BMI in adults increased 0.28 kg/m² per annum (95% CI, 0.03 to 0.5), and there was no significant change in BMI z-score in children (95% CI, −0.01 to 0.1). In the year after ivacaftor initiation, intravenous antibiotic treatment reduced by 46% (95% CI, −62.5% to −23.3%, oral antibiotic treatment reduced by 49% (95% CI, −61.1% to −32.1%), and there was no significant reduction in hospitalization (95% CI, −59.2% to 9.7%).

Conclusions: In this study of real-world CF registry data, clinical outcomes improved and healthcare resource utilization decreased after commencing ivacaftor.