Objective. To assess the long-term safety, immunogenicity, and efficacy of subcutaneous (SC) abatacept in combination with methotrexate (MTX) in Japanese patients with rheumatoid arthritis who were MTX inadequate responders, in a long-term extension (LTE) to a double-dummy, double-blind study (NCT01001832). Methods. Patients, who had previously received SC or intravenous (IV) abatacept with MTX (6-8 mg/week) for 24 weeks, received SC abatacept (125 mg/week) with MTX for an additional 52 weeks. Safety, immunogenicity, and efficacy were assessed. Results. The LTE included 112 patients. SC abatacept was generally well tolerated in the LTE, with no new safety signals. American College of Rheumatology 20, 50, and 70 response rates, disease activity score 28 (C-reactive protein) remission rates (< 2.6), and Health Assessment Questionnaire-Disability Index response rates (≥ 0.3 improvement from baseline) achieved at the end of the double-blind period were maintained over the LTE and were comparable in patients who received SC or IV abatacept in the double-blind period. Seropositivity for immunogenicity occurred in 4 (3.6%) patients. Self-injection of SC abatacept was well controlled and not associated with additional safety events. Conclusions. SC abatacept had acceptable safety and was well tolerated and effective over the LTE (76 weeks in total), with low rates of immunogenicity in Japanese patients.
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