Comparative Effectiveness of Azathioprine Versus Cyclosporine as an Initial Treatment for Idiopathic Inflammatory Myopathies: A Population-Based Observational Study.

OBJECTIVE To compare the effectiveness of azathioprine (AZA) and cyclosporine (CsA) as initial treatments for patients with idiopathic inflammatory myopathies (IIM). METHODS A retrospective cohort study was conducted using information from the National Health Insurance Service database of Republic of Korea. Patients with IIM who had started AZA or CsA as initial treatment between January 2007 and December 2011 were selected for the study. They were followed from the day of treatment initiation to the occurrence of study outcomes or the end of the study until December 2016. Effectiveness outcomes, defined as switching the drug or adding immunosuppressants, and discontinuation of corticosteroids, were compared between the two groups. The Cox proportional-hazards model was used to calculate the adjusted relative risk (aRR) with 95% confidence interval (CI) between the AZA and CsA groups. RESULTS A total of 376 patients with incident IIM who used AZA (n = 288) or CsA (n = 88) were identified. The aRR of switching the drug or adding immunosuppressants (1.45 [95% CI 0.99-2.11]) was not significantly different between the CsA and AZA groups. Among patients who were treated with corticosteroids at baseline, the rate of discontinuation of corticosteroids was not different between the two groups (1.69 [95% CI 0.82-3.47]). CONCLUSIONS The effectiveness of AZA and CsA as initial treatments for the management of IIM was comparable.