Rescue therapy within the UK Cystic Fibrosis registry: an exploration of the predictors of intravenous antibiotic use amongst adults with CF

Background and objective: Intravenous (i.v.) antibiotics are needed for rescue when preventative therapy fails to achieve stability among adults with cystic fibrosis (CF). Understanding the distribution of i.v. days can provide insight into the care that adults with CF need. We aim to determine the baseline characteristics that are associated with higher i.v. use, in particular to test the hypothesis that prior-year i.v. use is associated with future-year i.v. use. Methods: This is a cross-sectional analysis of the 2013–2014 UK CF registry data. Stepwise logistic regression was performed using current-year i.v. days as the dependent variable, and demographic variables including prior-year i.v. days as the covariates. Based on these results, study sample was divided into clinically meaningful subgroups using analysis similar to tree-based method. Results: Data were available for 4269 adults in 2013 and 4644 adults in 2014. Prior-year i.v. use was the strongest predictor for current-year i.v. use followed by forced expiratory volume in 1 s (FEV1). Adults with high prioryear i.v. use (>14 days) continued to require high levels of i.v., regardless of FEV1. Those with high prior-year i. v. use and FEV1 ≥70% had higher current-year i.v. days compared to adults with low prior-year i.v. use and FEV1 <40% (28 days, interquartile range (IQR): 11–41 days vs 14 days, IQR: 0–28 days; Mann–Whitney P-value <0.001 in 2013). Conclusion: CF people with prior high levels of rescue often continue to need high levels of rescue even if they have good FEV1. The reasons for this require further investigations.