A low-intervention prospective-retrospective study to evaluate the pharmacokinetics of Elexacaftor/Tezacaftor/Ivacaftor combination in a cystic fibrosis population

The goal of this clinical trial is to support the development of personalized therapy tailored to each patient's individual characteristics. A better understanding of the pharmacokinetic profiles of elexacaftor, tezacaftor, and ivacaftor is essential to support Therapeutic Drug Monitoring (TDM) and to guide dose adjustments when clinically indicated, without compromising therapeutic efficacy. The study will include male and female patients aged ≥6 years with Cystic Fibrosis (CF) carrying at least one F508del mutation and receiving treatment with the elexacaftor/tezacaftor/ivacaftor combination for a sufficient period to achieve steady state. The main objective of the study is to characterize the steady-state plasma concentration profiles of elexacaftor, tezacaftor, and ivacaftor in patients with Cystic Fibrosis treated with the elexacaftor/tezacaftor/ivacaftor combination. Participants will continue their usual treatment with elexacaftor/tezacaftor/ivacaftor and ivacaftor according to the prescribed dosing schedule. During the study, they will attend regular clinical visits every 3 months for up to 12 months. At these visits, blood samples will be collected as part of routine clinical care and used to measure the plasma concentrations of the study drugs. Additional blood samples may be collected after the morning dose to better characterize drug levels over time. In a subset of participants, additional blood samples may be collected at several time points during the day to further assess the pharmacokinetic profile of the drugs. A single additional blood sample may be collected for pharmacogenetic analyses. Participants may also undergo a nasal brushing, as part of routine procedures, to obtain nasal epithelial cells for further analyses. Clinical information, including routine laboratory tests, vital signs, treatment information and any adverse events, will be collected throughout the study. The results of the pharmacokinetic and other laboratory analyses will not be used to modify the participant's treatment, which will remain under the responsibility of the treating physician.