Rationale Patients with idiopathic pulmonary fibrosis and emphysema may have artificially preserved lung volumes. Objectives This post-hoc analysis investigated the relationship between baseline emphysema and fibrosis extents, and pulmonary function changes over 48 weeks. Methods Data were pooled from two Phase III, randomized, double-blind, placebo-controlled trials of interferon γ-1b in idiopathic pulmonary fibrosis (GIPF-001 [NCT00047645]; GIPF-007 [NCT00075998]). Patients with Week 48 data, baseline high-resolution computed tomography images and forced expiratory volume in 1 second/forced vital capacity ratios <0.8 or >0.9 (<0.7 or >0.9 in GIPF-007) and randomly selected patients with ratios 0.8-0.9 and 0.7-0.8 were included. Changes from baseline in pulmonary function at Week 48 were analyzed by emphysema extent. The relationship between emphysema and fibrosis extents and pulmonary function changes was assessed using multivariate linear regression. Measurements and Main Results Emphysema was identified in 38% of patients. A negative correlation was observed between fibrosis and emphysema extents (r = -0.232; P < 0.001). In quartile analysis, patients with the greatest emphysema extent (28%-65%) showed the smallest forced vital capacity decline, with a difference of 3.32% at Week 48 versus patients with no emphysema (P = 0.047). In multivariate analyses, emphysema extent ≥15% was associated with significantly reduced forced vital capacity decline over 48 weeks versus no emphysema/emphysema <15%. No such association was observed for carbon monoxide diffusing capacity or composite physiologic index. Conclusions Forced vital capacity measurements may not be appropriate to monitor disease progression in patients with idiopathic pulmonary fibrosis and emphysema extent ≥15%. Clinical trial registration available at www.clinicaltrials.gov, IDs NCT00047645 and NCT00075998.
