Inclusion Criteria:  Written Informed Consent Form to participate in the study; Men and women aged 18-75 years inclusive at the time of signing the Informed Consent Form; Documented diagnosis of ITP with a disease duration of more than 12 months from the moment of confirmation of the diagnosis by bone marrow aspirate or biopsy results;  A. For patients who have not had splenectomy:  established absence/loss of response to therapy with at least one drug of fist-line treatment for chronic ITP (which include GCs an IVIG); OR the occurrence of side effects during the course of therapy with the drug of the fist-line, making it impossible to use it further;  B. For patients who underwent splenectomy:  • loss/lack of response to splenectomy;  Thrombocytopenia ≥30.0 x 109/L - <50.0 x 109/L with severe hemorrhagic syndrome or thrombocytopenia <30.0 x 109/l, regardless of the presence of hemorrhagic syndrome, according to the results of platelet count conducted in a local laboratory for 7 days before the start of therapy with investigational or reference drug; Patients receiving GCs, azathioprine and danazole should receive these drugs in a maintenance dose for at least 4 weeks before starting therapy with investigational or reference drug; Consent of study participants with preserved childbearing function to use reliable methods of contraception (a combination of at least two methods, including 1 barrier method, for example, the use of a condom and spermicide) from the moment of signing the Informed Consent Form and 3 months after the last administration of investigational or reference drug.  Exclusion Criteria:  Hypersensitivity to the components of investigational or reference drug or E. coli proteins ; Unresolved severe hemorrhagic syndrome requiring emergency treatment at the time of initiation of study or reference drug therapy ; Fisher-Evans Syndrome; Conditions with a high risk of thromboembolic complications ; Myelodysplastic syndrome and/or bone marrow transplantation in anamnesis; Deviations of clinical and laboratory parameters according to the results of studies of blood samples taken during the screening period; Positive test results for hepatitis B, hepatitis C, or human immunodeficiency virus (HIV); Pregnancy or breastfeeding;  Use of drugs:  romiplostim used less than 3 weeks before treatment with study or reference drug; IVIG - less than 2 weeks prior to initiation of study or reference drug therapy; eltrombopag - used less than 2 weeks before treatment with study or reference drug, or planned to use eltrombopag while the patient is participating in this study; rituximab - used less than 14 weeks before treatment with study or reference drug, or planned to use rituximab while the patient is enrolled in this study; cyclophosphamide, cyclosporine, vincristine, vinblastine and other drugs used to treat chronic ITP not listed above and not included in the list of drugs approved for use during the study - use less than 8 weeks before the start of therapy with the study or reference drug or the use of any of these drugs is planned during the patient's participation in this study; preparations of any hematopoietic growth factors - use less than 8 weeks before the start of therapy with an investigational or reference drug; Influenza vaccines - less than 21 days prior to start of treatment with study or reference drug; vaccines to prevent novel coronavirus disease (COVID-19) - completion of the vaccination program less than 21 days prior to the start of study or reference drug therapy; other vaccines - less than 8 weeks prior to start of treatment with study or reference drug; Splenectomy within 12 weeks prior to screening; Participation in any clinical trials and/or use of unregistered drugs within 4 weeks prior to screening or 5 drug half-lives (whichever is greater); Any other disease or condition that, in the opinion of the investigator, may preclude the patient from participating in the study.