Long-term effects of ivacaftor on nonpulmonary outcomes in individuals with cystic fibrosis, heterozygous for a S1251N mutation

Objectives: To describe the long-term effects of ivacaftor (Kalydeco®) in individuals with cystic fibrosis (CF) on body mass index (BMI), body composition (BC), pulmonary function (PF), resting energy expenditure (REE), and exercise capacity (EC) after ≥12 months of treatment. Working Hypothesis: BMI, lean and fat mass, PF, and EC will increase and REE will decrease after treatment. Study Design: Observational study. Methodology: Seven individuals with CF (mean age 15.4 ± 5.8 years) heterozygous for S1251N mutation, starting with ivacaftor, were included. Paired t tests were performed to assess the effects of ivacaftor. Height and weight were used to calculate BMI and BMI Z-scores. Dual-energy X-ray absorptiometry was used to assess BC. Spirometry and body plethysmography were used to assess PF. Indirect calorimetry was used to measure REE and cardiopulmonary exercise testing (CPET) was used to measure oxygen uptake (VO_2peak), peak work rate (W_peak), and other CPET variables. Results: After a median of 15 (interquartile range: 13-16) months of treatment, BMI increased significantly (P =.03), but not BMI Z-score (P =.23) or BC. Significant improvements were found for several PF variables, especially measures of hyperinflation (P =.02). Absolute VO_2peak (P =.01), VO_2peak related to body weight (P =.00), and oxygen cost of work (P =.01) decreased. Absolute W_peak (P =.59) and W_peak related to body weight (P =.31) remained stable. Conclusions: The results showed that long-term treatment of ivacaftor is associated with improvement of BMI and PF, but not of BC and REE. Oxygen uptake reduced after treatment, which may be due to a decrease in work of breathing.