Predictors of pulmonary exacerbation treatment in cystic fibrosis

Background: Most studies of pulmonary exacerbations (PEx) in cystic fibrosis (CF) focus on intravenous (IV)-treated PEx, though most PEx are treated with oral antibiotics. Our objectives were to describe predictors of antibiotic choice and outcomes for PEx initially identified in clinic. Methods: For each patient in the U.S. CF Foundation Patient Registry, we selected the first PEx recorded at a clinic visit in 2013-14 following a clinic visit without a PEx. We used multivariable logistic regression to determine associations between clinical characteristics and antibiotic treatment choice. We determined outcomes in the 90 days after the first PEx. Results: Among 14,265 patients with a PEx initially identified in clinic, 21.4% received no antibiotics, 61.5% received new oral and/or inhaled antibiotics, and 17.0% had IV antibiotics within 14 days. Compared to IV antibiotics, patients more likely to receive new oral and/or inhaled antibiotics: were male, 10th percentile or 18.5 kg/m2, >90 days between clinic visits, FEV1 > 70% predicted at the PEx, no prior-year IV-treated PEx, FEV1 decline <10% predicted, and private insurance. Following the PEx, 30.3% of patients had no clinical encounters within 90 days. Treatment with IV antibiotics within 90 days occurred for 23.7% treated without antibiotics, 22.8% of new oral and/or inhaled antibiotics, and 27.1% of IV antibiotics. Conclusion: Most PEx identified in clinic are treated with new oral and/or inhaled antibiotics. Markers of disease severity are associated with antibiotic treatment choice. Many patients had no follow-up evaluation within 90 days of treatment

Lung Function Decline in Cystic Fibrosis: Impact of Data Availability and Modeling Strategies on Clinical Interpretations

RATIONALE: Studies estimating rate of lung function decline in cystic fibrosis (CF) have been inconsistent regarding methods used. How the methodology used impacts validity of the results and comparability between studies is unknown. OBJECTIVES: The Cystic Fibrosis Foundation established a workgroup whose tasks were to examine the impact of differing approaches to estimating rate of decline in lung function and to provide analysis guidelines. METHODS: We utilized a natural history cohort of 35,252 individuals with CF aged > 6 years of the Cystic Fibrosis Foundation Patient Registry (CFFPR), 2003-2016. Modeling strategies using linear and nonlinear forms of marginal and mixed-effects models, which have previously quantified rate of forced expiratory volume in 1 second (FEV1) decline (% predicted/year), were evaluated under clinically relevant scenarios of available lung function data. Scenarios varied by sample size (overall CFFPR, medium-sized cohort of 3,000 subjects, and small-sized cohort of 150), data collection/reporting frequency (encounter, quarterly, and annual), inclusion of FEV1 during pulmonary exacerbation, and follow-up length (<2 years, 2-5 years, entire duration). RESULTS: Rate-of-FEV1-decline estimates (% predicted/year) differed between linear marginal and mixed-effects models; overall cohort estimates (95% confidence interval) were 1.26 (1.24-1.29) and 1.40 (1.38-1.42), respectively. Marginal models consistently estimated less rapid lung function decline than mixed-effects models across scenarios except for short-term follow-up (both were ~1.4). Rate-of-decline estimates from nonlinear models diverged by age 30. Among mixed-effects models, nonlinear and stochastic terms fit best except for short-term follow-up (< 2 years). Overall CFFPR analysis from a joint longitudinal-survival model implied that an increase in rate of decline of 1% predicted/year in FEV1 associated with a 1.52-fold (52%) increase in the hazard of death/lung transplantation, but results exhibited immortal cohort bias. CONCLUSIONS: Differences were as high as 0.5% predicted/year between rate-of-decline estimates, but we found estimates were robust to lung function data availability scenarios except short-term follow-up and older age ranges. Inconsistencies among previous study results may be attributable to inherent differences in study design, inclusion criteria, or covariate adjustment. Results-based decision points reported herein will support researchers in selecting a strategy to model lung function decline most reflective of nuanced, study-specific goals