A Phase 3, open-label, 96-week trial to study the safety, tolerability, and efficacy of tezacaftor/ivacaftor in children ≥ 6 years of age homozygous for F508del or heterozygous for F508del and a residual function CFTR variant.

Background: Two previous Phase 3 studies ("parent studies") showed that tezacaftor/ivacaftor was generally safe and efficacious for up to 24 weeks in children 6 through 11 years of age with cystic fibrosis (CF) and F508del/F508del (F/F) or F508del/residual function (F/RF) genotypes. We assessed the safety and efficacy of tezacaftor/ivacaftor in an open-label, 96-week extension study.

Methods: This was a Phase 3, 2-part, multicenter, open-label, extension study in children 6 through 11 years of age at treatment initiation (Study VX17-661-116; NCT03537651). The primary endpoint was safety and tolerability. Secondary endpoints were absolute change from baseline in lung clearance index (LCI), sweat chloride (SwCl) concentration, Cystic Fibrosis Questionnaire-Revised (CFQ-R) respiratory domain score, and body mass index (BMI).

Results: One-hundred thirty children enrolled and received ≥ 1 dose of tezacaftor/ivacaftor; 109 completed treatment. Most (n = 129) had ≥ 1 treatment-emergent adverse event (TEAE), the majority of which were mild or moderate in severity and generally consistent with common manifestations of CF. Exposure-adjusted TEAE rates were similar to or lower than those in the parent studies. Five (3.8%) had TEAEs leading to treatment discontinuation. Efficacy results from the parent studies were maintained, with improvements in lung function, SwCl concentration, CFQ‑R respiratory domain score, and BMI observed from parent study baseline to Week 96.

Conclusions: Tezacaftor/ivacaftor is generally safe and well tolerated, and treatment effects are maintained for up to 120 weeks. These results support long-term use of tezacaftor/ivacaftor in children ≥ 6 years of age with CF and F/F or F/RF genotypes.