The impact of elexacaftor/tezacaftor/ivacaftor on body composition in a small cohort of youth with cystic fibrosis

Background: The effects of elexacaftor-tezacaftor-ivacaftor (ETI) on body composition in people with CF (pwCF) are unknown. Methods: Dual-energy X-ray absorptiometry fat-free mass and fat mass adjusted for height (FMI) as well as oral glucose tolerance test derived measures of insulin secretion and sensitivity were compared before and after ETI initiation in eight pwCF. Results: Patients median age: 22 years interquartile range (IQR: 16–28), 87.5% male, median time on ETI:11 months. Weight z-score increased from −0.52 to 0.18 (p = 0.014); FMI increased from 4.12 to 6.29 (p = 0.014). Insulin secretion (C pep iAUC/Gluc iAUC) increased from 8.71 to 14.21 (p = 0.021), insulin resistance (HOMA2 IR) increased from 0.73 to 1.25 (p = 0.014) and insulin sensitivity decreased (Matsuda) 8.88 to 5.58 (p = 0.036). Conclusions: ETI resulted in increased weight and fat mass. BMI and muscle mass did not change. Both insulin secretion and insulin resistance increased. Longer-term metabolic consequences of ETI need further investigation.