Supplementary Material for: Azathioprine for Connective Tissue Disease-Associated Interstitial Lung Disease

Background: Immunosuppressive therapy still is the standard treatment for patients with connective tissue disease-associated interstitial lung disease (CTD-ILD). Objectives: This retrospective study aimed to provide data on the tolerability and efficacy of azathioprine in progressive CTD-ILDs. Methods: A total of 56 patients with CTD-ILD treated with azathioprine between 2003 and 2014 were included in the study. The patients were assessed every 3 months during follow-up. Results: The mean treatment duration was 34 months, with a range of 3–105 months. Fifteen patients (27%) discontinued treatment due to side effects, mostly due to elevated liver enzymes, within the first 3 months. Forty-one patients were treated for longer than 3 months, and 27 of those (66%) had stabilization or improvement of pulmonary function during treatment. In patients who remained stable or improved, the mean FVC was 62 ± 17% predicted (% pred) at initiation of treatment and 65 ± 17% pred at the last follow-up visit (p = 0.036), and the mean DLCO was 38 ± 16% pred at initiation of treatment and 39 ± 17% pred at the last follow-up visit (p = 0.06). Conclusions: Azathioprine can stabilize or improve CTD-ILD. While early drug intolerance is frequent, most patients who have tolerated the drug well achieve long-term stabilization or improvement of lung function.