Acetylcysteine has been suggested as a beneficial treatment for idiopathic pulmonary fibrosis, although data from placebo-controlled studies are lacking.

In our initial double-blind, placebo-controlled trial, we randomly assigned patients who had idiopathic pulmonary fibrosis with mild-to-moderate impairment in pulmonary function to receive a three-drug regimen of prednisone, azathioprine, and acetylcysteine; acetylcysteine alone; or placebo. The study was interrupted owing to safety concerns associated with the three-drug regimen. The trial continued as a two-group study (acetylcysteine vs. placebo) without other changes; 133 and 131 patients were enrolled in the acetylcysteine and placebo groups, respectively. The primary outcome was the change in forced vital capacity (FVC) over a 60-week period.

At 60 weeks, there was no significant difference in the change in FVC between the acetylcysteine group and the placebo group (−0.18 liters and −0.19 liters, respectively; P=0.77). In addition, there were no significant differences between the acetylcysteine group and the placebo group in the rates of death (4.9% vs. 2.5%, P=0.30 by the log-rank test) or acute exacerbation (2.3% in each group, P>0.99).

As compared with placebo, acetylcysteine offered no significant benefit with respect to the preservation of FVC in patients with idiopathic pulmonary fibrosis with mild-to-moderate impairment in lung function. (Funded by the National Heart, Lung, and Blood Institute and others; ClinicalTrials.gov number, NCT00650091.)