Objective: The primary objective of this study was to evaluate the tolerability of single and multiple doses of abatacept in Japanese patients with rheumatoid arthritis. Secondary objectives included evaluating its pharmacokinetics, pharmacodynamics, immunogenicity, and efficacy. Methods: This dose-escalation, single- and multiple-dose, multicenter, open-label study was conducted at nine sites in Japan. Seven patients were enrolled at each of three dose levels (2, 8 and 16 mg/kg) and received a single intravenous dose of abatacept on day 1 of the single-dose phase. The multiple-dose phase, at the same dose, started once the patients had completed the single-dose phase and when it was confirmed that there were no safety issues. Results: Twenty patients started the single-dose phase. Single and multiple doses of abatacept were well tolerated, and adverse events were of mild to moderate intensity. There were no discontinuations or deaths due to adverse events. The pharmacokinetics of abatacept were linear, with no notable accumulation. There were no immunogenic effects on the safety, efficacy, or pharmacokinetics of abatacept. Multiple doses of abatacept improved individual items of the American College of Rheumatology core set. Conclusion: Single and multiple doses of abatacept showed favorable tolerability and efficacy in Japanese patients with rheumatoid arthritis.
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