Key Inclusion Criteria:

• Diagnosis of chronic ITP defined by: Failure to find other causes of thrombocytopenia; Platelet count ≤ 150 x 10^9/L over 6 months or response to a previous treatment with subsequent decrease in platelet count even if duration of chronic ITP is less than 6 months
• Platelet counts ≤ 20 x 10^9/L

Key Exclusion Criteria:

• Planned splenectomy throughout the study period
• Treatment with IVIG or anti-D immunoglobulin within 3 weeks prior to screening
• Treatment with immunosuppressive or other immunomodulatory drugs within 3 weeks prior to screening
• Treatment with intravenous steroids within 10 days prior to screening
• Change of oral steroid treatment within 15 days prior to screening
• Patients with known or suspected hypersensitivity to immunoglobulins or previous severe side effects to immunoglobulin therapy
• Abnormal results in the following laboratory parameters: Hemoglobin < 10 g/dL; Total bilirubin > 1.5 x upper normal limit; ALAT > 2.5 x upper normal limit; ASAT > 2.5 x upper normal limit; Creatinine > 1.5 x upper normal limit; Urea > 1.5 x upper normal limit
• Positive direct Coombs test
• Patients with one of the following concomitant diseases Clinical active SLE Known or suspected HIV infection Acute hepatitis Clinically active chronic hepatitis Lymphoproliferative disease Heart failure Grade III or IV according to the New York Heart Association classification
• Any other concomitant disease that has influence on the clotting system (i.e. hemophilia)