background and importance In patients with cystic fibrosis (CF), long-term adherence to various treatments is considered low (46%–70%). Cystic fibrosis transmembrane conductance regulator (CFTR) modulators have recently been licensed. Low adherence to these treatments may decrease efficacy.

Aim and objectives To assess adherence to CFTR modulators and determine if there are differences because of length of treatment.

Material and methods Retrospective observational study of CF patients under treatment with a CFTR modulator (tezacaftor/ivacaftor; elexacaftor/tezacaftor/ivacaftor; lumacaftor/ivacaftor) dispensed at the outpatient unit of the Children’s Hospital Pharmacy Service, between January 2020 and April 2021. Demographic variables (age and sex), prescription and dispensing dates, and amount dispensed were obtained from the electronic prescription records. Adherence was calculated using the medication possession ratio (MPR). MPR ≥ 80% was considered adequate adherence. Continuous variables were expressed as mean (SD) or median (Q1-Q3), and categorical variables as absolute and relative frequency. A non-parametric test of comparison of proportions was used to assess the relationship between adherence and length of treatment (less or greater than 12 months). Statistical analysis was performed with Stata version 13.

Results Eighty-two patients (36 women, 43.9%), 67 (81.7%) of whom were adults with a median of 31.2 years (Q1-Q3 = 26.1–39.0) and 15 (18.3%) were children or adolescents with a median of 11.6 years (Q1-Q3 = 7.6–15.6). Treatments dispensed were: tezacaftor/ivacaftor + ivacaftor (61 patients; 74.4%), elexacaftor/tezacaftor/ivacaftor + ivacaftor (13 patients; 15.9%) and lumacaftor/ivacaftor (8 patients; 9.8%). At the time of analysis, 55 patients (67.1%) had been in treatment for less than 12 months and 27 (32.9%) more than 12 months.The mean MPR was 102.7% (SD 11.5%). Eighty-one patients (98.7%) had adequate adherence. The mean MPR in the group lasting less than 12 months was 104.8% (SD 11.7%) and 98.3% (SD 9.7%) in those lasting more than 12 months (p=0.327).

Conclusion and relevance Adherence to CFTR modulators is higher than observed for other drugs in CF patients, but there is a need to study whether adherence with these drugs is maintained in the long term. Although there were no differences in adherence according to the length of treatment, the only patient considered non-adherent was on treatment greater than 12 months.

Conflict of interest No conflict of interest