LAUSR

Access to cystic fibrosis transmembrane conductance regulator (CFTR) modulators has been gradually increasing for people with cystic fibrosis, the first of which was ivacaftor, a CFTR potentiator that is part of all clinically available modulator treatments. In this study, we hypothesized that the steady‐state concentrations in blood and tissue are highly variable in patients taking ivacaftor in a real‐world context, which may have an impact on the treatment approach. We collected nasal epithelial cells to estimate target site concentrations and blood samples to estimate pharmacokinetic parameters at a steady state. We found that patients on ivacaftor monotherapy have variable concentrations well above the maximal effective concentration and may maintain concentrations necessary for the clinical benefit even if dosing is reduced. We also are the first to provide detailed target site concentration data over time, which shows that tissue concentrations do not fluctuate significantly and do not correlate with plasma concentrations. These findings show that some patients may have higher‐than‐expected concentrations and may benefit from tailored dosing to balance clinical response with side effects or adherence needs.