Objectives OSKIRA-4 evaluated the efficacy of fostamatinib monotherapy versus placebo on the signs and symptoms of rheumatoid arthritis over 6 weeks by Disease Activity Score C reactive protein (DAS-28(CRP)) and assessed non-inferiority to adalimumab monotherapy at Week 24 by DAS-28(CRP).

Methods Overall, 279 patients not currently taking disease-modifying antirheumatic drugs were randomised to: (A) fostamatinib 100 mg twice daily for 24 weeks plus placebo injection every 2 weeks (PBOI); (B) fostamatinib 100 mg twice daily for 4 weeks, then 150 mg once daily up to Week 24, plus PBOI; (C) fostamatinib 100 mg twice daily for 4 weeks, then 100 mg once daily up to Week 24, plus PBOI; (D) adalimumab 40 mg every 2 weeks for 24 weeks, plus oral placebo twice daily; or (E) oral placebo twice daily for 6 weeks, plus PBOI, then a switch to arm A or B.

Results Fostamatinib demonstrated a significant improvement in DAS-28(CRP) score from baseline versus placebo at Week 6 for arms A and B, but not C. Fostamatinib was significantly less effective than adalimumab at Week 24 based on DAS-28(CRP). Adverse events observed with fostamatinib treatment were consistent with those reported in previous studies, including hypertension and diarrhoea.

Conclusions Fostamatinib demonstrated efficacy as monotherapy, showing superior DAS-28(CRP) score changes between baseline and 6 weeks when compared with placebo in treatment arms A and B. However, all fostamatinib regimens demonstrated inferior responses compared with adalimumab at Week 24.

Trial registration number Clinicaltrials.gov: NCT01264770.