A randomized, phase IIa treatment delayed-start trial of the oral JAK 1/2 inhibitor, baricitinib, in adult idiopathic inflammatory myopathy

Objectives To assess the effects of 24 weeks active treatment with baricitinib, a JAK1/2 inhibitor, in adult idiopathic inflammatory myopathy (IIM). Methods Patients with active dermatomyositis (DM) or polymyositis (PM) were enrolled into a 1:1 randomized treatment delayed-start design clinical trial (NCT04208464). Participants received 24 weeks baricitinib plus 12 weeks follow-up (Immediate-start), or 12 weeks standard of care plus 24 weeks baricitinib (Delayed-start). The primary outcome was clinical response after 24 weeks active treatment, defined as minimal improvement (Total Improvement Score >20 [TIS20]). Secondary outcomes included: TIS40 (moderate), TIS60 (major) response, between-arm comparison, time to achieve response, change in clinical outcome measures. steroid-sparing and cumulative adverse events. Results 14/15 (93%) randomized participants (mean age 43.2 years [11.6 SD]; 13 DM, 2 PM; 11 female) completed the study (baseline to 36 weeks) and all achieved TIS20 at 24 weeks post-active treatment (95% exact CI 0.68-1.00). 9/15 (60%) achieved TIS40 response and 2/15 (13%) TIS60 response. At 12 weeks post-randomization, 11/15 (73%) patients achieved at least TIS20 (95%CI 0.45-0.92), including all Immediate-start arm patients and four Delayed-start arm patients. At the same time point, evidence of a difference was noted for patient global, extramuscular, CDASI skin activity, pain, fatigue and SF-36 mental/physical health scores. Two hospitalisation serious adverse events were documented, neither related to study drug. Conclusions Treatment of IIM with baricitinib resulted in improved clinical outcome after 24 weeks. Significant improvement after 12 weeks treatment was also evident. No significant safety concerns were raised. A randomized placebo-controlled trial is needed to confirm the efficacy in patients with IIM.