Transition to KPL-387 Monotherapy Dosing & Administration Study

During the Posology (Dosing and Administration) Study, participants on oral pericarditis therapies alone (i.e., non-steroidal anti-inflammatory drugs \[NSAIDs\], colchicine, and/or glucocorticoids) and participants on Interleukin-1 (IL-1) pathway inhibition drugs will transition to KPL-387 per protocol guidelines. Participants will receive KPL-387 for up to 16 weeks in the Posology Study. At study visits throughout the Posology Study, participants will be queried for symptoms of chest pain (and participants will fill out pericarditis pain numerical rating scale \[NRS\] scores) and will be assessed for physical signs (e.g., pericardial friction rub) and laboratory evidence of pericarditis activity (e.g., C-reactive protein \[CRP\]) as well as treatment tolerability and pharmacokinetics (PK). Participants experiencing new or worsening symptoms consistent with pericarditis will be managed per study protocol. All active, enrolled participants in the Posology Study who have not completed an End of Treatment (EOT) Visit may be eligible to transition into the Long-Term Extension (LTE) following completion of the Week 16 Visit. The Week 16 Visit will serve as both a Posology Study End of Study Visit and a Baseline Visit for the LTE. Participants who choose not to participate in the LTE will complete an EOT Visit followed by a Safety Follow-Up until 8 weeks after the last KPL-387 dose administration. The open-label LTE is designed to evaluate the long-term efficacy and safety of KPL-387 in recurrent pericarditis (RP). Treatment in the LTE may continue until the participant has received up to 24 months of treatment in the LTE or until KPL-387 is approved for commercial use in that region to treat pericarditis, whichever occurs first. At study visits throughout the LTE, participants will be queried for symptoms of chest pain (and participants will fill out pericarditis pain NRS scores) and will be assessed for physical signs (e.g., pericardial friction rub) and laboratory evidence of pericarditis activity (e.g., CRP) as well as treatment tolerability and PK. Participants experiencing new or worsening symptoms consistent with pericarditis will be managed as described in the protocol.