A Study to Assess the Efficacy and Safety of Efgartigimod in Adult Patients With Primary Immune Thrombocytopenia (ITP).

Inclusion criteria: * Ability to understand the requirements of the trial, to provide written informed consent (including consent for the use and disclosure of research-related health information), and to comply with the trial protocol procedures (including required trial visits). * Male or female patient aged ≥18 years. * Confirmed ITP diagnosis, at least 3 months before randomization and according to the American Society of Hematology Criteria, and no known other etiology for thrombocytopenia. * Diagnosis supported by a response to a prior ITP therapy (other than thrombopoietin receptor agonists \[TPO-RAs\]), in the opinion of the investigator. * Mean platelet count of \<30×10E9/L from 2 counts: 1 platelet count collected during the screening period and the predose platelet count on the day of randomization. * At the start of the trial, the patient is either on concurrent ITP treatment(s) and has received at least 1 prior therapy for ITP in the past, or the patient is not on treatment for ITP but has received at least 2 prior treatments for ITP. Patients receiving permitted concurrent ITP treatment(s) at baseline, must have been stable in dose and frequency for at least 4 weeks prior to randomization. * Women of childbearing potential must have a negative serum pregnancy test at the screening visit and a negative urine pregnancy test at baseline before trial medication (infusion) can be administered. * Women of childbearing potential should use a highly effective or acceptable method of contraception during the trial and for 90 days after the last administration of the IMP. Exclusion criteria: * ITP/thrombocytopenia associated with another condition, eg, lymphoma, chronic lymphocytic leukemia, viral infection, hepatitis, induced or alloimmune thrombocytopenia, or thrombocytopenia associated with myeloid dysplasia. * Use of certain medications before the start of the studies (more details in the protocol) * Patients who have a history of malignancy, including malignant thymoma, or myeloproliferative or lymphoproliferative disorders, unless deemed cured by adequate treatment with no evidence of recurrence for ≥3 years before screening. Patients with completely excised non-melanoma skin cancer (such as basal cell carcinoma or squamous cell carcinoma) or cervical carcinoma in situ would be permitted at any time. * Uncontrolled hypertension, defined as a repeated elevated blood pressure exceeding 160 mmHg (systolic) and/or 100 mmHg (diastolic) despite appropriate treatments. * History of any major thrombotic or embolic event within 12 months prior to randomization. * History of coagulopathy or hereditary thrombocytopenia or a family history of thrombocytopenia. * History of a recent or planned major surgery (that involves major organs eg, brain, heart, lung, liver, bladder, or gastrointestinal tract) within 4 weeks of randomization. * Positive serum test at screening for an active viral infection with any of the following conditions: Hepatitis B virus (HBV), Hepatitis C virus (HCV), Human immunodeficiency virus (HIV) * Clinical evidence of significant unstable or uncontrolled acute or chronic diseases other than ITPdespite appropriate treatments which could put the patient at undue risk. * Patients with known medical history of hypersensitivity to any of the ingredients of the IMP. * Patients who previously participated in a clinical trial with efgartigimod and have received at least 1 administration of the IMP. * Pregnant or lactating females. More details in the protocol