Study to Assess the Efficacy and Safety of Rilonacept Treatment in Participants With Recurrent Pericarditis

The primary objective of this study was to assess the efficacy of rilonacept treatment in participants with recurrent pericarditis.

In the single-blind run-in (RI) period, rilonacept 320 mg (or 4.4 mg/kg in pediatric participants ≥12 and \<18 years old) subcutaneous (SC), followed by 160 mg (or 2.2 mg/kg in pediatric participants ≥12 and \<18 years old) injections once weekly.

During the Randomized-Withdrawal (RW) period, eligible participants are randomized 1:1 to double-blinded administration of study drug:

* Rilonacept 160 mg (or 2.2 mg/kg in pediatric participants ≥12 and \<18 years old) SC injections once weekly
* Matching placebo SC injections once weekly.

Participants with pericarditis recurrence who meet the protocol criteria for bailout rilonacept (report at least 1 day with pericarditis pain ≥4 on the 11-point numerical rating scale (NRS) and have 1 C-reactive protein (CRP) value ≥ 1 mg/dL \[either on the same day or separated by no more than 7 days\]) receive bailout rilonacept (2 open-label injections of 160 mg rilonacept \[or 4.4 mg/kg for pediatric subjects\]) irrespective of randomized treatment assignment and as soon as at least 5 days have passed since the last study drug injection.

Upon completion of the RW period (i.e., when the prespecified number of primary efficacy endpoints \[clinical events committee-confirmed pericarditis recurrence\] events have occurred), all participants who did not discontinue study drug have an option to continue treatment with open-label rilonacept in the Long-Term Extension (LTE) or to withdraw from the study. Participants still in the RI period at the time that the RW period has ended and the LTE is opened will have the option to enter the LTE directly when they have completed the RI period and have met the definition of clinical response or to withdraw from the study.

Eligibility Criteria:
Key Inclusion Criteria:

1. Male or female aged 12 or older
2. Has a diagnosis of recurrent pericarditis
3. Must provide Informed Consent
4. Presents with at least the third episode of pericarditis during screening.
5. Has received nonsteroidal anti-inflammatory drugs (NSAIDs) and/or colchicine and/or corticosteroids (in any combination), if used, at stable dose levels (or at least not increased) for at least 3 days prior to first study drug administration
6. Female subjects must be postmenopausal, or incapable of pregnancy or permanently sterile, or if of childbearing potential must agree to use highly-effective method of contraception.
7. Must be up-to-date with all immunizations, in agreement with current local immunization guidelines for immunosuppressed subjects, before first study drug administration.
8. Is able to adequately maintain a daily subject diary according to protocol.
9. Agrees to refrain from making any new, major lifestyle changes that may affect pericarditis symptoms (e.g., changing exercise pattern) from the time that the informed consent form (ICF) is signed through the end of the double-blind randomized withdrawal period.

Key Exclusion Criteria:

1. Has a diagnosis of pericarditis that is secondary to specific prohibited etiologies.
2. Has a history of immunosuppression, including positive human immunodeficiency virus (HIV) test results.
3. Has a history of myeloproliferative disorder.
4. Has a history of demyelinating disease or symptoms suggestive of multiple sclerosis.
5. Has a history of active or latent tuberculosis (TB) prior to screening
6. Has chest x-ray at screening or within 12 weeks before receiving first administration of study drug, with evidence of malignancy or abnormality consistent with prior or active TB infection.
7. Has a history of positive or intermediate results for hepatitis B surface antigen, hepatitis B core antibody, or hepatitis C virus antibody at screening.
8. 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).
9. Has a known or suspected current active infection or a history of chronic or recurrent infectious disease, including, but not limited to, chronic renal infection, chronic chest infection, sinusitis, recurrent urinary tract infection, or an open, draining infected skin wound.
10. Has had an organ transplant.
11. In the Investigator's opinion, has a history of alcoholism or drug/chemical abuse within 2 years before screening.
12. Has a known hypersensitivity to rilonacept or to any of its excipients.
13. Has received an investigational drug during the 30 days before screening or is planning to receive an investigational drug (other than that administered during this study) or use an investigational device at any time during the study.
14. In the Investigator's opinion, has any other medical condition that could adversely affect the subject's participation or interfere with study evaluations.