Rationale: A previous trial of bosentan in idiopathic pulmonary fibrosis (IPF) showed a trend to delayed IPF worsening or death. Also, improvements in some measures of dyspnea and health-related quality of life were observed.

Objectives: To demonstrate that bosentan delays IPF worsening or death.

Methods: Prospective, randomized (2:1), double-blind, placebo-controlled, event-driven, parallel-group, morbidity–mortality trial of bosentan in adults with IPF of less than 3 years’ duration, confirmed by surgical lung biopsy, and without extensive honeycombing on high-resolution computed tomography. The primary endpoint was time to IPF worsening (a confirmed decrease from baseline in FVC ≥ 10% and diffusing capacity of the lung for carbon monoxide ≥ 15%, or acute exacerbation of IPF) or death up to End of Study. Effects of bosentan on health-related quality of life, dyspnea, and the safety and tolerability of bosentan were investigated.

Measurements and Main Results: Six hundred sixteen patients were randomized to bosentan (n = 407) or placebo (n = 209). No significant difference between treatment groups was observed in the primary endpoint analysis (hazard ratio, 0.85; 95% confidence interval, 0.66–1.10; P = 0.2110). No treatment effects were observed on health-related quality of life or dyspnea. Some effects of bosentan treatment were observed in changes from baseline to 1 year in FVC and diffusing capacity of the lung for carbon monoxide. The safety profile for bosentan was similar to that observed in other trials.

Conclusions: The primary objective in the Bosentan Use in Interstitial Lung Disease-3 trial was not met. Bosentan was well tolerated.

Clinical trial registered with www.clinicaltrials.gov (NCT 00391443).