Efficacy and Tolerability of Generic Pirfenidone After Switch from Esbriet® in Idiopathic Pulmonary Fibrosis: A Real-World Observational Study

Background Generic formulations of pirfenidone are increasingly adopted in idiopathic pulmonary fibrosis (IPF), yet real-world evidence supporting their clinical equivalence to the originator remains limited. We aimed to evaluate whether switching from branded pirfenidone (Esbriet®) to a generic formulation affects treatment efficacy or tolerability. Methods We conducted a retrospective, within-patient observational study including consecutive patients with IPF treated with Esbriet® for ≥ 6 months before switching to generic pirfenidone. Pulmonary function was assessed at three time points: 6 months before the switch (T − 6), at switch (T0), and 6 months after (T + 6). The primary endpoint was the within-patient percentage change in FVC over two consecutive 6-month periods (T − 6→T0 vs T0→T + 6), analysed within a pre-specified equivalence framework (± 5 percentage points). Secondary endpoints included DLCO changes and treatment-related adverse events (AEs), analysed at the patient level using paired comparisons. Results. Sixty-five patients (median age 77.0 years [72.3–80.0] years, 78% male) had complete functional follow-up. The mean percentage decline in FVC was − 1.9% before the switch and − 1.7% after the switch. The estimated between-period difference in FVC change was 0.2 percentage points (95% CI − 1.1 to 1.5), fully contained within the pre-specified equivalence margins. Similar findings were observed for DLCO, with no significant difference between periods. Overall, 43% of patients experienced at least one AE during treatment. Gastrointestinal AEs were the most frequent, but paired analyses showed no significant difference in patient-level AE occurrence between branded and generic periods. No severe AEs or treatment discontinuations were observed. Conclusions In this real-world cohort of patients with IPF, switching from branded to generic pirfenidone was not associated with clinically meaningful differences in lung function decline or treatment tolerability.