Long-term safety and efficacy of rilonacept in patients with systemic juvenile idiopathic arthritis

Objective: To determine the long-term safety and efficacy of rilonacept, an anti-interleukin-1 fusion protein, in patients with active systemic juvenile idiopathic arthritis (JIA).

Methods: In patients with systemic JIA, ages 4-20 years, the efficacy of rilonacept was evaluated using 30%, 50%, and 70% levels of improvement according to the adapted American College of Rheumatology (ACR) Pediatric 30, 50, and 70 response criteria, respectively. Efficacy and safety were evaluated during 23 months of open-label treatment (3 phases) after a 4-week, double-blind, placebo-controlled phase. Following double-blind treatment with 2.2 mg/kg or 4.4 mg/kg of rilonacept, patients were eligible to receive open-label treatment at their prior dose, with adjustments. Reductions in the median daily dose of oral prednisone and improvements in laboratory parameters of disease activity (i.e., decreased levels of D-dimer and myeloid-related proteins [MRPs]) were also evaluated.

Results: Twenty-four patients entered the double-blind study and 23 entered the open-label period. Patients were predominantly white and female, and had a median age of 14.0 years at baseline. No significant differences in efficacy were observed between the rilonacept- and placebo-treated patients during the double-blind phase, but fever and rash completely resolved by month 3 in all patients during the open-label treatment period and did not recur. Adapted ACR Pediatric 30, 50, and 70 response rates at 3 months from the start of the study were 78.3%, 60.9%, and 34.8%, respectively; these responses were generally maintained over the study duration. Levels of D-dimer and MRP-8/MRP-14 dramatically improved during the study, and in 22 of 23 patients, the prednisone dose was decreased or prednisone therapy was discontinued. No serious treatment-related adverse events were observed.

Conclusion: Sustained improvements in clinical and laboratory measures of the articular and systemic manifestations of systemic JIA were achieved in >50% of rilonacept-treated patients over 2 years. Treatment with rilonacept had a substantial steroid-sparing effect and was generally well-tolerated.