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);~scheduled treatment period - 24-60 weeks (depends on the duration of treatment with RPH-104 during the main study CL04018068);~safety follow-up period - 72 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).~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, such patients should attend a safety follow-up visit 6 weeks after the screening period (i.e. 8 weeks after the last injection of the study drug or placebo during the main study CL04018068) with all procedures performed in accordance with the last planned safety follow-up visit (corresponds to Safety Follow-up Visit (SFV)), after which their participation in the study will be considered completed. 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.~The duration of the open-label scheduled therapy with the test drug (prior to transition to the follow-up safety period) will be 24 to 60 weeks depending on the duration of RPH-104 use during the main study (CL04018068).~After the patients receive the last dose of the study drug the treatment period will be considered completed and a 72 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).~In case of a suspected recurrence of pericarditis (for example, fever, characteristic pain), 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:~the chest pain intensity score according to the numeric rating scale (NRS) > 3 (in the absence of other possible reasons for the increase in the pain intensity);~C-reactive protein (CRP) level > 5 mg/L (in the absence of other possible reasons for an increase in CRP levels);~development of a new pericardial effusion or progression of the existing one in diastole according to echocardiography (EchoCG).~If recurrence of the disease is confirmed during the treatment period as well as if any of the above-described signs of relapse of pericarditis and its persistence (two consecutive visits) or a tendency to increase the values of the sign (estimated at two consecutive visits) are are detected, therapy with the study drug could be canceled ahead of schedule or continued at a dose of 80 mg every 2 weeks with the addition of NSAIDs and / or colchicine at the discretion of the Investigator.~If the patient develops a pericarditis recurrence during the safety follow-up period, at the discretion of the investigator treatment with the study drug might be re-initiated in this patient or therapy with alternative drugs of the researcher's choice might be prescribed (in this case, the patient will have to come to two follow-up visits - 4 and 8 weeks after the last dose of the study drug. After that the patient will be considered to have completed the study). In case of study drug re-initiation, the drug will be administered according to the following regimen: a single dose of 160 mg (first injection) followed by a dose of 80 mg 7 days and 14 days after the first injection and at doses of 80 mg every two weeks thereafter (at the discretion of the investigator). At the discretion of the investigator, NSAIDs and/or colchicine might be used for the treatment of recurrences in these patients. The duration of re-initiated therapy will be 60 weeks. The use of RPH-104, as well as Non-steroidal anti-inflammatory drugs (NSAIDs) and/or colchicine (if they have been used for the treatment of the disease recurrence) may be continued or discontinued at the discretion of the investigator if deemed necessary.~The assessment of the patient's condition will be carried out 3 days, 7 and 14 days, as well as 12 weeks after the continuation of the study therapy with the addition of NSAIDs and / or colchicine during the therapy period or after the study drug re-initiation during the safety monitoring period. The criterion for the resolution of the relapse is the presence of all the following signs simultaneously:~the chest pain intensity score according to the numeric rating scale (NRS) ≤ 3 AND~CRP level ≤ 5 mg/L AND~absence or small (<10 mm) pericardial effusion or progression of the existing one in diastole according to echocardiography (EchoCG).~If the recurrence of the disease is resolved by the week 12, the patient will continue to use RPH-104 80 mg every 2 weeks and will conduct efficacy and safety assessments every 2 weeks for 12 weeks and thereafter every 4 weeks until the end of the scheduled treatment period or re-initiated therapy, depending on the period the study when the recurrence occurred. If glucocorticoid prescription is required by week 12 to resolve a recurrence, the investigated therapy will be canceled to the patient ahead of schedule.~If the patient develops a pericarditis recurrence after the study drug re-initiation (the patient already receives RPH-104 80 mg every 2 weeks during the safety monitoring period), as well as if any of the signs of a relapse of pericarditis and its persistence or a tendency to increase the values of the sign (as described above for the period of planned therapy), the use of RPH-104 might be canceled ahead of schedule or continued until the end of the period of re-initiated therapy at a dose of 80 mg every 2 weeks with the addition of NSAIDs and/or colchicine at the discretion of the investigator.~After the end of the re-initiated therapy, the patient will have to come to two follow-up visits - 4 or 8 weeks after the last dose of the study drug.~No decrease or increase in the doses of the study drug (other than those described in this study) are envisaged in this study.~Patients who have discontinued the open-label therapy with the study drug early for any reason, should perform two safety follow-up visits at Week 4 and Week 8 after the last dose of the study drug.~The duration of one patient participation in this open study is from 96 to 200 weeks, depends on the duration of the therapy period, which will be calculated for each patient, taking into account the duration of the RPH-104 use during the main study (CL04018068), as well as on the absence or presence of a pericarditis recurrence and the decision to resume the studied therapy in the safety follow-up period of the study.
The goal of this clinical trial is to evaluate the safety and efficacy of RPH-104 for long-term use in a population of patients with idiopathic recurrent pericarditis who completed the main study CL04018068.~The primary objective of the study is to evaluate the safety of RPH-104 80 mg once every 2 weeks in patients with idiopathic recurrent pericarditis who completed the main study.