Sarilumab plus methotrexate in patients with active rheumatoid arthritis and inadequate response to methotrexate: results of a randomized, placebo-controlled phase III trial in Japan

Background Sarilumab is a human immunoglobulin G1 anti-interleukin-6 (IL-6) receptor monoclonal antibody that blocks IL-6 from binding to membrane-bound and soluble IL-6 receptor α. This bridging study assessed the efficacy and safety of sarilumab + methotrexate (MTX) in Japanese patients with active rheumatoid arthritis (RA) and inadequate response to MTX (MTX-IR). Methods In this phase III study, 243 patients were randomized 2:2:1:1 to receive subcutaneous sarilumab 150 mg every 2 weeks (q2w), sarilumab 200 mg q2w, placebo switching to sarilumab 150 mg q2w + MTX at 24 weeks, or placebo switching to sarilumab 200 mg q2w at 24 weeks, all in combination with MTX, for a total of 52 weeks (double-blind, placebo-controlled 24-week period followed by a single-blind 28-week extension). The primary endpoint was the proportion of patients achieving American College of Rheumatology 20% improvement criteria (ACR20) responses at week 24. Results ACR20 response rates at week 24 were 67.9%, 57.5%, and 14.8% for sarilumab 150 mg, sarilumab 200 mg, and placebo, respectively. Serious treatment-emergent adverse events were reported by 9.9%, 6.3%, 0%, and 13.3% of patients in the sarilumab 150 mg, sarilumab 200 mg, placebo to sarilumab 150 mg, and placebo to sarilumab 200 mg groups, respectively. No deaths occurred. The incidence of infections ranged from 52.5 to 67.9%, with five serious infections for the sarilumab 150 mg group and one for the group switched from placebo to 200 mg sarilumab. Absolute neutrophil count < 1.0 Giga/l occurred in 13.6% and 7.5% of patients in the sarilumab 150 and 200 mg groups, respectively, and was not associated with infection. Conclusions In Japanese MTX-IR RA patients treated with sarilumab (150 and 200 mg q2w) in combination with MTX, sustained clinical efficacy was shown by significant improvement in signs, symptoms, and physical function; bridging between this and a previous global study was achieved. At week 52, the safety profiles of both doses of sarilumab were generally similar, as previously observed and as expected based on IL-6 class. Trial registration ClinicalTrials.gov, NCT02293902 . Registered on 19 November 2014. Electronic supplementary material The online version of this article (10.1186/s13075-019-1856-4) contains supplementary material, which is available to authorized users.