Non-adherence to treatments for chronic diseases may jeopardize patients' health, increase costs of care, and cause unnecessary clinic appointments and diagnostic studies, as well as additional treatments with potentially serious side effects. Little is known about adherence to methotrexate in pediatric rheumatology. Because this medication is commonly used in JIA, we assessed adherence among children receiving methotrexate in two countries. A total of 76 outpatients (M:F 21:55) with JIA seen in Rio de Janeiro (Brazil) and in Boston (US) taking methotrexate for >2 months were enrolled. Questionnaires were completed by the parents from both centers. Non-adherence was defined as omission of ≥3 prescribed doses in the previous 8 weeks. Patients' ages ranged from 1 to 17 years. Mean time on methotrexate was 20.5 months (±25). Overall rate of non-adherence was 18%. The rate of reported non-adherence was 8% in Boston and 24% in Rio de Janeiro (P = 0.012). The main reason for non-adherence in Boston was "child refused"; in Rio de Janeiro, the main reason was inability to obtain medication. Age had a negative association with adherence (P < 0.0001). Sex, time on methotrexate, route of administration, or concomitant use of other medications were not associated with adherence. Eighteen percent of children with JIA prescribed methotrexate were non-compliant. The difference in reasons for poor adherence between patients in Rio de Janeiro and Boston suggests that different strategies may be needed to improve adherence in these 2 settings. The rate of non-adherence warrants further investigation.

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