Longitudinal effects of ivacaftor and medicine possession ratio in people with the Gly551Asp mutation: a 5-year study

Abstract

Introduction: Ivacaftor was the first therapy licensed to address the underlying defect in cystic fibrosis (CF). The improvements in lung function, nutritional status and pulmonary exacerbations in patients carrying a Gly551Asp mutation were greater than previously seen in clinical trials for other therapies. Limited data are available regarding long-term outcomes and adherence to ivacaftor outside clinical trials.

Methods: We conducted a 5-year single-centre retrospective study of people with CF carrying the Gly551Asp mutation who received ivacaftor. Clinical outcome data were extracted from medical notes and databases. Drug delivery data were used to assess medicine possession ratio (MPR).

Results: 35 people were included. After commencing ivacaftor, FEV₁ improved by 9.6% (SE±1.59%) predicted by 6 months. Thereafter, FEV₁ declined, and at 5 years had returned to pre-ivacaftor baseline. Ivacaftor did not alter annual rate of FEV₁ decline (1.57% pre vs 1.82% post, p=0.74). Body mass index (BMI) increased for 4 years. There was a significant reduction in inpatient and total intravenous antibiotic days sustained over 5 years. MPR remained high but declined over time (-2.5±0.9% per year, p=0.007). FEV₁ was better maintained in patients with higher MPRs.

Conclusion: The addition of ivacaftor provides acute benefits for people with the Gly551Asp mutation and established lung disease. We report a sustained reduction in intravenous antibiotic use but following acute improvement in lung function, decline continues, and patients will continue to require medical observation and optimisation. Strategies to maintain high adherence should be a priority to prolong the benefits of ivacaftor.

Keywords: cystic fibrosis.