A Phase II Clinical Trial of Low-Dose Inhaled Carbon Monoxide in Idiopathic Pulmonary Fibrosis.

Background: Preclinical studies have demonstrated that low-dose carbon monoxide (CO) can abrogate experimental lung fibrosis. To test the therapeutic role of inhaled CO, we designed a clinical study in patients with idiopathic pulmonary fibrosis (IPF).

Methods: We conducted a multicenter, phase IIa, double-blinded, sham-controlled, clinical trial. Patients with IPF were randomized to treatment with inhaled CO at 100 to 200 parts per million or to inhaled 21% oxygen for 2 h daily, twice weekly, for 12 weeks. The primary study end point was the difference in change in matrix metalloproteinase-7 (MMP7) serum concentration after 12 weeks of treatment. Secondary end points included pulmonary function test measures, 6-min walk distance, rates of adverse events, acute exacerbation, hospitalization and death, and quality of life measures.

Results: Fifty-eight subjects were randomized to treatment with inhaled CO (n = 29) or placebo (n = 29). Despite modest increases in CO blood levels, the change in MMP7 concentrations after 12 weeks of treatment did not significantly differ between the study arms (MMP7 difference at week 12, -0.90 ng/mL; 95% CI, -4.18 to 2.38 ng/mL). No differences were observed in physiologic measures, incidence of acute exacerbations, hospitalization, death, or patient-reported outcomes. Importantly, no differences in distribution of adverse events were noted between the treatment arms.

Conclusions: Inhaled CO is well tolerated and can be safely administered to patients with IPF in the ambulatory setting; however, inhaled CO did not result in significant changes in study end points. Our findings support testing the efficacy of inhaled therapies in future IPF clinical trials.

Trial Registry: ClinicalTrials.gov; No.: NCT01214187; URL: www.clinicaltrials.gov.