This Phase 3 study is designed to evaluate the efficacy and safety of romiplostim in combination with predniso(lo)ne compared with predniso(lo)ne alone in adults with 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.

De-identified individual patient data for variables necessary to address the specific research question in an approved data sharing request.

Data sharing requests relating to this study will be considered beginning 18 months after the study has ended and either 1) the product and indication have been granted marketing authorization in both the US and Europe or 2) clinical development for the product and/or indication discontinues and the data will not be submitted to regulatory authorities. There is no end date for eligibility to submit a data sharing request for this study.

Qualified researchers may submit a request containing the research objectives, the Amgen product(s) and Amgen study/studies in scope, endpoints/outcomes of interest, statistical analysis plan, data requirements, publication plan, and qualifications of the researcher(s). In general, Amgen does not grant external requests for individual patient data for the purpose of re-evaluating safety and efficacy issues already addressed in the product labelling. Requests are reviewed by a committee of internal advisors. If not approved, a Data Sharing Independent Review Panel will arbitrate and make the final decision. Upon approval, information necessary to address the research question will be provided under the terms of a data sharing agreement. This may include anonymized individual patient data and/or available supporting documents, containing fragments of analysis code where provided in analysis specifications. Further details are available at the URL below.