Background Idiopathic pulmonary fibrosis (IPF) is a severe and progressive interstitial lung disease (ILD). Treatment with the anti-fibrotic agent Pirfenidone slows decline in forced vital capacity (FVC). Pulmonary vasculopathy is a relatively common and life-limiting complication of IPF and is frequently associated with a reduction in the diffusing capacity of the lung for carbon monoxide (DLco). However, it is not known what effect Pirfenidone may have on DLco.

Methods We performed a retrospective analysis of patients with diagnoses of IPF on long term Pirfenidone treatment. Lung function data were collected at treatment initiation and then at 12 months, (6–18 months). To assess for a treatment effect, similar data were also collected from an untreated control cohort of biopsy proven IPF patients from the pre-Pirfenidone era managed at the same centre. Data were analysed using Stata.

Results 138 patients were studied; n = 66 patients in the untreated control group and n = 72 patients in the Pirfenidone treated group. The control group had a higher baseline predicted FVC (74.8% v 67.5%) (p < 0.05) but baseline predicted DLco measurements were similar (44% v 40%) (p = 0.19). 12 month relative FVC change was greater in the untreated group; 9.9% (273 mL) (±11.4%) versus 3.9% (123 mL) (±11.9%) (p < 0.005). 12 month relative DLco decline was also greater in the untreated group; 16.4% (±20.5%) versus 7.5% (±17.6%) (p < 0.01). In multivariate analyses, the effect of Pirfenidone treatment had a 6.7% impact on FVC change (2.7–10.6) (p < 0.001) and a 9.0% impact on DLco change (2.5–15.5) (p < 0.01). Right ventricular systolic pressure correlated with baseline predicted DLco (p < 0.005, r² = -0.14).

Discussion In this study we have demonstrated that over 12 months, Pirfenidone confers a reduction in gas transfer decline paralleling that seen for FVC. This treatment effect on DLco may be due to a combination of deceleration in ILD progression as well as attendant effects at the level of the pulmonary vasculature. This may have particularly relevance given the correlation between DLco and echocardiographic parameters of pulmonary vascular disease.

Conclusion Treatment of IPF with Pirfenidone markedly attenuates declines in gas transfer. This is of interest as it may provide insights into mechanisms underpinning disease stabilisation.