Objectives Cystic fibrosis is a devastating life-limiting genetic condition characterised by a progressive decline in lung function, respiratory infections and premature death. Tezacaftor-ivacaftor is a combined cystic fibrosis transmembrane conductance regulator (CFTR) modulator that targets the underlying cause of the disease. This study aimed to assess the impact of tezacaftor-ivacaftor use in routine clinical practice for adults with cystic fibrosis.

Methods A retrospective observational longitudinal cohort study design was applied to examine the clinical effect of tezacaftor-ivacaftor in routine practice in the West of Scotland Adult Cystic Fibrosis Unit. Adults receiving tezacaftor-ivacaftor for at least 4 weeks were included in this medicine use evaluation.

A standardised data form was used to collect patient-level data: demographics, genotype, complications of cystic fibrosis, medicine access process. Fifty-two weeks pre and post tezacaftor-ivacaftor initiation data: lung function, body mass index (BMI), days spent in hospital, days receiving antibiotic treatment for respiratory exacerbations. Anonymised data were collated and analysed using SPSS V.26.

Results Of 121 potential patients, 45 received treatment with tezacaftor-ivacaftor; median age 30 years (range 17–64) at initiation, 56% were male, 76% were deemed to be homozygote and 41 patients continued treatment for at least 52 weeks. There was no significant change in % predicted FEV₁; median difference 0 (IQR −3 to 6). There was a significant improvement in BMI, mean 0.6 kg/m² (95% CI 0.2 to 1.0), as well as a median 4 (IQR −17 to 0) day reduction in days in hospital and 21 (IQR −42 to 0) day reduction in days receiving antibiotics.

Conclusions The use of tezacaftor-ivacaftor in routine practice for people with cystic fibrosis was associated with improvements in weight, as well as reducing the number of days people needed to spend in hospital and receive antibiotics.