Transition to KPL-387 Monotherapy Dosing & Administration Study

Key Inclusion Criteria: * Has well-controlled recurrent pericarditis (i.e., including having CRP \< 0.5 mg/dL within 14 days of Baseline and a pericarditis pain NRS score ≤ 3 at Baseline) * Has a documented history of CRP elevation (\> 1 mg/dL) associated with at least one prior acute pericarditis episode, whether the incident event or any pericarditis recurrence * Has received treatment for RP for at least 3 months prior to Baseline with standard therapy(ies) and is currently on a stable dosing regimen including NSAIDs and/or colchicine, and/or glucocorticoids or an IL-1 pathway inhibitor (anakinra or rilonacept). Key Exclusion Criteria: * Has a diagnosis of pericarditis that is secondary to specific prohibited etiologies * Has had a pericarditis recurrence in the last 3 months prior to Baseline * Has received an investigational drug during the 4 weeks before study drug administration or is planning to receive an investigational drug at any time during the study. * Has a history of active or untreated, latent tuberculosis (TB) prior to screening. * Has a history of immunodeficiency. * Has a history of immunosuppression, including positive human immunodeficiency virus (HIV) test results. * Has chest x-ray at Screening or within 12 weeks before first study drug administration, with evidence of malignancy, abnormality consistent with prior or active TB infection or active infection. * Has a history of malignancy of any organ system within the past 5 years before Screening (other than a successfully treated non-metastatic cutaneous squamous cell carcinoma or basal cell carcinoma and/or localized carcinoma in situ of the cervix). * Has a known or suspected current active infection or a history of chronic or recurrent infectious disease (\> 3 episodes in prior 12 months), including but not limited to, genitourinary infection, chest infection, sinusitis, or skin/soft tissue infection. * Has had a serious infection, has been admitted to the hospital for an infection, or has been treated for a documented infection requiring antibiotics for a documented infection within 2 weeks prior to first study drug administration. * Has had an organ transplant (except corneal transplant performed more than 3 months prior to first study drug administration). * In the Investigator's opinion, has any other medical condition that could adversely affect the subject's participation or interfere with study evaluations.