Inclusion Criteria:
* Signed informed consent to participate in the study.
* male or female
* Age ≥18 years
* Diagnosis of primary immune thrombocytopenia (PIT).
* Duration of PIT at the Screening Visit: for cohort 1: ≥3 months; for cohort 2: ≥6 months.
* PIT therapy with glucocorticosteroids (GCS) for cohort 1: duration of continuous therapy ≥3 months at the Screening Visit or ≥2 courses of pulse therapy during the year before the Screening Visit;
* TPO-RA therapy: for cohort 1: no history of TPO-RA use; for Cohort 2: Use of TPO-RA for ≥12 weeks at the Screening Visit;
* No increase in TPO-RA dose during the 4 weeks preceding the end of screening.
* Blood platelet count: for cohort 1: mean platelet count ≤30×10\*9/L, based on the last two measurements 7±2 days apart, each of which had a platelet count ≤35×10\*9/L OR steroid dependence, defined as the use of prednisolone at a daily dose of \>5 mg (or another corticosteroid at an equivalent dose) for ≥2 months before the Screening Visit to maintain a platelet count ≥30×10\*9/L OR to prevent bleeding; for cohort 2: platelet count ≥50×10\*9/ml for ≥6 weeks out of the last 8 weeks of follow-up with platelet counts every 7±2 days and no emergency treatment for severe hemorrhagic syndrome in the last 12 weeks before the Screening Visit.
* Consent and ability to comply with the procedures of the Protocol, as well as the prohibitions and restrictions provided for by the Research Protocol.
Exclusion Criteria:
* Hypersensitivity to romiplostim.
* History of TPO-RA use: for cohort 1: any TPO-RA; for cohort 2: any TPO-RA, with the exception of romiplostim and eltrombopag.
* Unpromising treatment with romiplostim in the opinion of the Researcher
* Splenectomy \<24 weeks prior to the Screening Visit or planned splenectomy during the study.
* Treatment with rituximab within the 14 weeks preceding the Screening Visit, or planned treatment with rituximab during the study.
* Treatment with intravenous immunoglobulin or anti-D immunoglobulin during the 2 weeks preceding the Screening Visit, or planned use during the study.
* Therapy with hematopoietic growth factors during the 4 weeks preceding the Screening Visit, or their planned use during the study.
* Therapy with alkylating chemotherapy drugs during the 8 weeks preceding the Screening Visit, or their planned use during the study.
* Use of other medicines listed in section 5.3.3. of this study protocol.
* Participation in a clinical trial of an investigational drug or investigational medical device within 4 weeks or 5 half-lives (whichever is longer) preceding the Screening Visit.
* Secondary immune thrombocytopenia in the following diseases: autoimmune thyroiditis, systemic lupus erythematosus (SLE), antiphospholipid syndrome (APLS), lymphoproliferative diseases, drug-mediated, viral origin (herpes viruses, HIV, chronic viral hepatitis).
* Hereditary thrombocytopenia.
* Diseases of the hematopoietic system accompanied by thrombocytopenia (for example, acute leukemia, aplastic anemia, myelodysplastic syndrome, lymphoproliferative diseases).
* Metastatic bone marrow lesions.
* Uncontrolled concomitant diseases of internal organs.
* Arterial thrombosis (for example, myocardial infarction, acute cerebrovascular accident) within 1 year preceding the Screening Visit.
* History of venous thrombosis.
* High risk of venous thrombosis and thromboembolism, defined as the presence of at least three of the following risk factors:
* diabetes;
* smoking;
* use of combined oral contraceptives or menopausal hormone therapy;
* positive titer of antiphospholipid antibodies;
* hypercholesterolemia (\>240 mg/dl or \>13 mmol/l);
* hypertriglyceridemia;
* arterial hypertension requiring therapy.
* HIV infection.
* Viral hepatitis B or C.
* Oncological and/or oncohematological disease beyond the stage of complete 5-year remission at the Screening Visit.
* Major surgery ("major surgery") within 8 weeks preceding the Screening Visit, or incomplete recovery from surgery at the Screening Visit.
* Pregnancy or lactation in women.
* Hospitalization for any reason planned during the patient's participation in the study.
* A history of mental disorders that do not allow you to adequately assess your behavior and follow the conditions of the study protocol.
* Alcoholism. Alcoholism or consumption of alcohol in quantities exceeding for men: 14 units. per week (on average); for women: 7 units. per week (on average).
