Effects of Fostamatinib, an Oral Spleen Tyrosine Kinase Inhibitor, in Rheumatoid Arthritis Patients With an Inadequate Response to Methotrexate Results From a Phase III, Multicenter, Randomized, Double-Blind, Placebo-Controlled, Parallel-Group Study

Objective. This phase III, 52-week study compared fostamatinib with placebo (for 24 weeks) in patients with active rheumatoid arthritis (RA) and an inadequate response to methotrexate (MTX) therapy. Methods. Patients taking MTX were randomized (1: 1: 1) to receive fostamatinib 100 mg twice daily for 52 weeks (group A), fostamatinib 100 mg twice daily for 4 weeks and then 150 mg once daily (group B), or placebo for 24 weeks and then fostamatinib 100 mg twice daily (group C). At week 24, the co-primary end points were change from baseline in the American College of Rheumatology 20% (ACR20) improvement response rates and change in the modified total Sharp/van der Heijde score of radiographic damage (SHS). Results. In this study, 918 patients were randomized and received > 1 dose of study drug (fostamatinib or placebo); the demographic and baseline clinical characteristics were well balanced. Following treatment with both fostamatinib regimens, a statistically significant difference in the ACR20 improvement response was achieved at week 24 as compared with that in patients receiving placebo (49.0% [group A] and 44.4%, [group B] versus 34.2%; P < 0.001 and P 0.006, respectively), but there was no statistically significant difference in the SHS between either fostamatinib group and placebo (P 0.25 and P 0.17, respectively). The most common adverse events in patients in groups A, B, and C were hypertension (15.8%, 15.1%, and 3.9%, respectively) and diarrhea (13.9%, 15.1%, and 3.9%, respectively). Elevated blood pressure (> 140/90 mm Hg) occurred at > 1 visit in 44.2%, 41.6%, and 19.3% of patients in each respective group. Conclusion. With the use of either fostamatinib regimen in patients with RA, statistically significant, but not clinically significant, improvements in the ACR20 improvement response over placebo were achieved at 24 weeks, whereas a significant difference in the SHS was not seen. The overall level of response to treatment with fostamatinib was lower than had been observed in the phase II program, but similar adverse events were reported.