Antifibrotics and mortality in idiopathic pulmonary fibrosis: external validity and avoidance of immortal time bias

Abstract

Background and objective Pooled analyses of previous randomized controlled trials reported that antifibrotics improved survival in patients with idiopathic pulmonary fibrosis (IPF), but the results were only based on short-term outcome data from selected patients who met strict criteria. Observational studies/meta-analyses also suggested that antifibrotics improve survival, but these studies failed to control for immortal time bias that considerably exaggerates drug effects. Therefore, whether antifibrotics truly improve long-term survival in patients with IPF in the real world remains undetermined and requires external validity. Methods We used data from the Japanese National Claims Database to estimate the intention-to-treat effect of antifibrotics on mortality. To address immortal time bias, we employed models treating antifibrotic initiation as a time-dependent covariate and target trial emulation (TTE), both incorporating new-user designs for antifibrotics and treating lung transplantation as a competing event. Results Of 30,154 patients with IPF, 14,525 received antifibrotics. Multivariate Fine–Gray models with antifibrotic initiation as a time-dependent covariate revealed that compared with no treatment, nintedanib (adjusted hazard ratio [aHR], 0.85; 95% confidence interval [CI], 0.81–0.89) and pirfenidone (aHR, 0.89; 95% CI, 0.86–0.93) were associated with reduced mortality. The TTE model also replicated the associations of nintedanib (aHR, 0.69; 95% CI, 0.65–0.74) and pirfenidone (aHR, 0.81; 95% CI, 0.78–0.85) with reduced mortality. Subgroup analyses confirmed this association regardless of age, sex, and comorbidities, excluding certain subpopulations. Conclusions The results of this large-scale real-world analysis support the generalizability of the association between antifibrotics and improved survival in various IPF populations.