The impact of elexacaftor/tezacaftor/ivacaftor on fat-soluble vitamin levels in people with cystic fibrosis

While elexacaftor/tezacaftor/ivacaftor (ETI) has improved the pulmonary health of many people with cystic fibrosis (PwCF), less is known about ETI effectiveness for extra-pulmonary manifestations, including fat-soluble vitamin malabsorption. This study aims to evaluate ETI's impact on vitamin A, D, E, and international normalized ratio (INR, an indirect marker for Vitamin K) serum levels. Retrospective cohort study of PwCF ≥12 years receiving ETI. Vitamin levels up to four years preceding and up to two years following ETI initiation were collected. Pairwise comparisons of vitamin levels pre/post-ETI initiation were made using Wilcoxon signed rank and McNemar's tests. Linear mixed effect models were used to regress vitamin levels on time since starting ETI, ETI use (yes/no), the interaction between time and ETI use, and age. Two hundred and sixty-four participants met study inclusion, and 169 (64%) had post-ETI initiation vitamin levels. Median vitamin A levels increased from 422.0 to 471.0 mcg/L (p < 0.001), median vitamin D levels increased from 28.5 to 30.8 ng/mL (p = 0.003), and there were no significant changes in median vitamin E or INR. Vitamin A levels rose at a rate of 40.7 mcg/L/year (CI 11.3, 70.2) after ETI start. ETI initiation is associated with increased median vitamin A and vitamin D levels, but no change in median vitamin E or INR levels. Ongoing monitoring of vitamin levels after ETI initiation is needed to screen for potential deficiencies and toxicities, particularly in light of case reports of hypervitaminosis A following ETI initiation.