A Study of Romiplostim Plus Predniso(lo)ne vs. Predniso(lo)ne Alone for the Treatment of Previously Untreated Primary Immune Thrombocytopenia (ITP)

Inclusion Criteria: * Age ≥18 years or adult legal age within country if older than 18 years. * Diagnosis of primary ITP according to the 2019 International Consensus (ICR) that is previously untreated and requires treatment. * Note: The investigator should ensure that the diagnosis of primary ITP is established by excluding other causes of isolated thrombocytopenia, as outlined in the 2019 ICR, which states that the diagnosis of primary ITP is principally based on the exclusion of other causes of isolated thrombocytopenia. * Note: If emergency treatment is necessary, platelet count performed before emergency can be used for study inclusion. * Note: Emergency ITP treatment with any thrombopoietin receptor agonists (TPO-RAs), or splenectomy is not allowed. * Platelet count \< 30 × 10\^9/L or Platelet count \< 50× 10\^9/L with clinically significant bleeding before any medical intervention. Exclusion Criteria: * Life-threatening bleeding at randomization. * Known sensitivity or intolerance to any of the products to be administered during study (eg, uncontrolled diabetes) or to any Escherichia coli-derived product (eg, filgrastim, pegfilgrastim, certain insulins). * Uncontrolled hypertension before randomization. * Abnormal hepatic or renal function at screening. * History of total splenectomy. * Use of concurrent anticoagulation therapy and/or antiplatelet therapy. * Need for nonsteroidal anti-inflammatory drugs (NSAIDs) use and use of NSAIDs within 7 days before randomization. * Venous or arterial thrombotic event within 3 or 6 months, respectively, before randomization. * Other protocol-defined Inclusion/Exclusion may apply.