• Is at least 18 years of age and the local legal age of consent for clinical studies when signing the informed consent form (ICF).

• Has documented baseline mean platelet count of \<30 x 10\^9/L before randomization

• Has a documented duration of primary immune thrombocytopenia (ITP) of more than 12 months on the date of informed consent form (ICF) signature.

• Has documented prior ITP treatment with at least 1 of the following treatments: corticosteroids, intravenous immunoglobulin (IVIg), anti-D immunoglobulin, thrombopoietin receptor agonist (TPO-RAs), or rituximab.

• Has documented insufficient response to a prior ITP treatment (the specific criteria can be found in the protocol).

• Has documented prior response defined as 1 platelet count of ≥50 × 109/L to at least 1 of the following ITP treatments in the 3 years before the date of ICF signature: prednisone, dexamethasone, other or nonspecified corticosteroids, IVIg, or anti-D immunoglobulin