BackgroundThe antimetabolites methotrexate (MTX) and mycophenolate mofetil (MMF) are commonly used as initial corticosteroid-sparing treatment for uveitis. There is little data examining risk factors for failing both MTX and MMF. The objective of this study is to determine risk factors for failing both MTX and MMF in patients with non-infectious uveitis.Main bodyThis is a sub-analysis of the First-line Antimetabolites as Steroid-sparing Treatment (FAST) uveitis trial, which was an international, multicenter, block-randomized, observer-masked, comparative effectiveness trial comparing MTX and MMF as initial treatments for non-infectious uveitis. This study was undertaken at multiple referral centers in India, the United States, Australia, Saudi Arabia and Mexico between 2013 and 2017. A total of 137 patients who completed all 12 months of follow-up from the FAST trial, were included in this study. The primary outcome was failing both antimetabolites over the 12 months of the trial. Potential predictors included: age, sex, bilateral involvement, anatomic location of the uveitis, presence of cystoid macular edema (CME) and retinal vasculitis at baseline visit, uveitis duration, and country/study sites as risk factors for failing both MTX and MMF. The presence of retinal vasculitis posterior to the equator on fluorescein angiogram was associated with failing both MTX and MMF.ConclusionRetinal vasculitis may be a risk factor for failing multiple antimetabolites. Clinicians could consider more quickly advancing these patients to other medication classes, such as biologics.