Interleukin-1 has been implicated as a mediator of recurrent pericarditis. The efficacy and safety of rilonacept, an interleukin-1α and interleukin-1β cytokine trap, were studied previously in a phase 2 trial involving patients with recurrent pericarditis.

We conducted a phase 3 multicenter, double-blind, event-driven, randomized-withdrawal trial of rilonacept in patients with acute symptoms of recurrent pericarditis (as assessed on a patient-reported scale) and systemic inflammation (as shown by an elevated C-reactive protein [CRP] level). Patients presenting with pericarditis recurrence while receiving standard therapy were enrolled in a 12-week run-in period, during which rilonacept was initiated and background medications were discontinued. Patients who had a clinical response (i.e., met prespecified response criteria) were randomly assigned in a 1:1 ratio to receive continued rilonacept monotherapy or placebo, administered subcutaneously once weekly. The primary efficacy end point, assessed with a Cox proportional-hazards model, was the time to the first pericarditis recurrence. Safety was also assessed.

A total of 86 patients with pericarditis pain and an elevated CRP level were enrolled in the run-in period. During the run-in period, the median time to resolution or near-resolution of pain was 5 days, and the median time to normalization of the CRP level was 7 days. A total of 61 patients underwent randomization. During the randomized-withdrawal period, there were too few recurrence events in the rilonacept group to allow for the median time to the first adjudicated recurrence to be calculated; the median time to the first adjudicated recurrence in the placebo group was 8.6 weeks (95% confidence interval [CI], 4.0 to 11.7; hazard ratio in a Cox proportional-hazards model, 0.04; 95% CI, 0.01 to 0.18; P<0.001 by the log-rank test). During this period, 2 of 30 patients (7%) in the rilonacept group had a pericarditis recurrence, as compared with 23 of 31 patients (74%) in the placebo group. In the run-in period, 4 patients had adverse events leading to the discontinuation of rilonacept therapy. The most common adverse events with rilonacept were injection-site reactions and upper respiratory tract infections.

Among patients with recurrent pericarditis, rilonacept led to rapid resolution of recurrent pericarditis episodes and to a significantly lower risk of pericarditis recurrence than placebo. (Funded by Kiniksa Pharmaceuticals; RHAPSODY ClinicalTrials.gov number, NCT03737110.).