Decision on Optimal Combinatorial Therapies in Immune-mediated inflammatory diseases using Systems approaches (DocTIS): protocol for a single-arm, adaptive basket trial in rheumatoid and psoriatic arthritis.

Objectives: Current treatments for rheumatoid arthritis (RA) and psoriatic arthritis (PsA) reduce disease activity but often fail to achieve sustained remission. The Decision on Optimal Combinatorial Therapies in Immune-mediated inflammatory diseases using Systems approaches (DocTIS) program has shown that additive anti-inflammatory effects in patients with arthritis can be achieved by combining tumour necrosis factor (TNF) and interleukin (IL)-6 inhibitor therapies. The goal was to provide proof-of-principle evaluation of whether combining TNF and IL-6 inhibitors shows a signal of activity on remission outcomes in RA and PsA. Methods: This is a single-arm, multicentre, adaptive basket trial recruiting 20 patients with RA and 20 with PsA and including 24 weeks of treatment and 10 weeks of safety follow-up. Eligible participants on TNF for ≥6 weeks will proceed with the addition of IL-6 inhibitor (tocilizumab) at 162 mg every 2 weeks for 8 weeks, increasing to weekly dosing in weeks 9-24 if well tolerated. The primary outcome is remission at 24 weeks (Clinical Disease Activity Index score ≤2.8 in RA and Disease Activity in PsA score <4). Secondary outcomes include safety, tolerability and disease activity assessments. Using Simon's two-stage design (80% power, one-sided α = 0.10), the trial aims to detect an increase in remission (10% to 30%). An interim futility analysis will occur after seven participants per basket reach 24 weeks. Conclusion: Findings from this proof-of-principle study will inform the feasibility and design of future randomised trials evaluating combination biologic therapy in inflammatory arthritis. Study registration: www.isrctn.com; ISRCTN50666516.