Alive and on Initial Antifibrotic Treatment: Real-World Treatment Durability in Idiopathic and Progressive Pulmonary Fibrosis

Background: Conventional antifibrotic treatment persistence reflects medication retention but may not fully capture whether patients remain both alive and on their initial therapy. We evaluated alive and on initial treatment (AOIT) as a clinically oriented measure of treatment durability in idiopathic pulmonary fibrosis (IPF) and progressive pulmonary fibrosis (PPF). Methods: This retrospective single-center cohort included adults with IPF or PPF treated with pirfenidone or nintedanib between 2018 and 2026. AOIT was defined as the time from antifibrotic initiation to permanent discontinuation/switching or death while known to remain on initial treatment. Kaplan–Meier and Cox regression analyses were performed. Results: Among 86 patients, 37 (43.0%) experienced AOIT loss, including 26 discontinuation/switch events and 11 deaths. AOIT was 75.1%, 63.6% and 46.9% at 12, 24, and 36 months, respectively; median AOIT was 34.9 months (95% CI 21.3–48.4). AOIT did not differ between nintedanib and pirfenidone (log-rank p = 0.395). First-drug persistence was 80.0%, 71.7%, and 61.7% at the corresponding time points, with a median of 52.2 months (95% CI 31.2–73.2). Malignancy (adjusted HR 5.00, 95% CI 1.91–13.09, p = 0.001) and higher baseline DLCO (adjusted HR 1.67 per 10-percentage-point increase, 95% CI 1.21–2.29; p = 0.002) were associated with AOIT loss. Conclusions: AOIT declined over time and was numerically lower than first-drug persistence, reflecting distinct aspects of longitudinal treatment durability. AOIT may complement medication-centered persistence in real-world antifibrotic treatment assessment.