Study of the Safety and Efficacy of RPH-104 in Preventing Recurrences in Patients With Idiopathic Recurrent Pericarditis

This long-term open-label study is an extension of the main double-blind, randomized, placebo-controlled study, CL04018068. This study will include the following periods:

* screening period - carried out on Day 0 (where Day 182, Week 26 from randomization in the main study CL04018068 will be considered as Day 0 of this study); * re-screening period - up to 28 days (for patients who have completed the CL04018077 study); * scheduled treatment period - 24-60 weeks (depends on the duration of treatment with RPH-104 during the main study CL04018068); * safety follow-up period - 168 weeks. 60-week treatment re-initiation is possible in case of a disease recurrence reported during this period (with follow-up assessments 4 and 8 weeks after the last dosing of the investigational drug and telephone visits after 20, 32, 44, 56, 68, 80, 92 and 104 weeks after the administration of the final dose of the investigational drug, respectively).

It is planned that this study will include no more than 25 patients who completed the main study.

During the screening period, patients will be evaluated for eligibility for inclusion/non-inclusion in this study. Patients who do not meet these criteria will not receive treatment with the study drug.

Patients who meet the criteria for inclusion/non-inclusion in the study will enter the treatment period, where they will start open-label treatment with RPH-104 80 mg once every 2 weeks subcutaneously (SC).

The study drug to patients will be administered by qualified medical personnel every 2 weeks when the patient visits the study site, or at the patient's home by the patient him/herself. Safety and efficacy assessments are performed at Visit 1, Visit 2 (after 2 weeks) and then every 4 weeks according to the visits schedule.

After the patients receive the last dose of the study drug the treatment period will be considered completed and a 168 week period of safety follow-up will start. During this period, the patients will have to visit the study site after 4 weeks, then - after 8 weeks, and thereafter - every 12 weeks if in the Investigator's opinion it is considered safe and acceptable for a particular patient (it is possible to conduct the visits every 4 weeks until the completion of the study, if necessary in the Investigator's opinion and in agreement with Sponsor). There will also be eight telephone visits.

In case of a suspected recurrence of pericarditis, the patient will need to contact the study physician and come to the study site for an unscheduled visit. Recurrence of pericarditis is defined as the presence of at least two of the following symptoms in a patient: