Background: Exercise tolerance is compromised in many patients with cystic fibrosis (CF). The 6-minute walk test (6MWT) is a simple test used to assess exercise tolerance.

Aims and objectives: We hypothesized that treatment with elexacaftor/tezacaftor/ivacaftor (ELX/TEZ/IVA), the drug leading to improvement in lung function, BMI and general well-being of CF patients, would be associated with improvement in exercise tolerance as well.

Methods: Children with CF treated for at least 6mo with ELX/TEZ/IVA were analysed. We compared the 6MWT walking distance (6MWD) prior to treatment and after 6mo. Descriptive statistics, paired t-test and Pearson correlation were applied.

Results: Twelve patients (median age 14yr, range 12-18) were included. 6MWD at 0 and 6mo  were 516.21±98.72m and 645.58±68.40m resp. (p < 0.001) with an average increase of 28.19%. A significant inverse correlation was observed between the starting 6MWD and the 6MWD increase (p = 0.002).

In a subgroup of 7 patients that were followed for one year we found that the exercise tolerance further improved: 6MWD at 0, 6, and 12mo were 476.36±61.90m, 640.71±54.58m and 658.14±56.35m, resp. (p < 0.001). However, average increase in 6MWD in the first half-year (+36.90%) was significantly higher (p = 0.017) than in the following 6mo (+3.24%). A significant inverse correlation between the starting 6MWD and the total 6MWD increase persisted after 1yr (p = 0.040).

Conclusions: Exercise tolerance is an important parameter of quality of life. A significant increase in 6MWD accompanies treatment with ELX/TEZ/IVA. The lower the exercise tolerance at the starting point, the better improvement in 6MWD during the course of treatment.