Inclusion Criteria:

1. Be aged between 18 and 82 at the time of written consent.

2. Have confirmed diagnosis of chronic ITP and fulfil all the following criteria:

   • irrelevant history except for the symptoms of bleeding,
   • pattern of bleedings associated with platelet disorders,
   • physical examination irrelevant for the ITP, except for the signs of bleeding,
   • isolated thrombocytopenia in the blood count; apart from thrombocytopenia, the blood count is normal for the patient's age, or if abnormal, readily explained,
   • peripheral blood smear consistent with ITP: thrombocytopenia with platelets of normal size or slightly larger than normal, with absence of platelet clumps and giant platelets; normal red blood cell and white blood cell morphology,
   • confirmed diagnosis of immune thrombocytopenic purpura or, when any abnormal finding is present, additional diagnostic evaluation excludes other causes of thrombocytopenia.
   • Previous known diagnosis of ITP for at least 3 months.
3. To show a platelet count platelet count < 30,000/µl at the moment of the first infusion with the study product.
4. Have read the patient information and consent sheet, agreed to participate in the trial, and signed the consent sheet.
5. Be expected to receive treatment over 5 days and follow-up for 3 months.
6. For women of childbearing age, use adequate contraceptive method such as oral contraceptives, intrauterine device (IUD) or tubal ligation during one-month period after the first infusion in the study.

Exclusion Criteria:

1. Have immune thrombocytopenia secondary to other pathologies or drug mediated thrombocytopenia.
2. Have a known diagnosis of other autoimmune diseases, established in the medical history and laboratory findings with positive results for the determination of antinuclear antibodies, anti-cardiolipin antibodies, lupus anticoagulant or direct Coombs test.
3. Present important active bleeding due to other reasons apart from the ITP.
4. Exhibit an identifiable alternative cause of their thrombocytopenia, such as splenomegaly, family thrombocytopenia, bacteraemia, sepsis or active infection requiring or not therapy.
5. Are presenting renal dysfunction.
6. Have non-controlled arterial hypertension.
7. Have documented liver cirrhosis or any hepatic disorder with ALT levels 2.5 times or more than the normal upper limit or bilirubin greater than 2 mg/dl.
8. Are presenting a cardiac disease including a history of coronary artery disease, angina pectoris or congestive heart failure.
9. Present known infection due to HIV or HCV.
10. Have been previously treated with IVIG or anti-D immunoglobulin being unresponsive.
11. Have a history of serious adverse reactions or non-serious but frequent adverse reactions to IVIG preparations or other products derived from blood.
12. Have known allergies to any IGIV3I Grifols components, such as D-sorbitol.
13. Are simultaneously participating in other clinical studies or have received an investigational drug in the 3 months prior to the start of the study.
14. Have been involved in the present study and being treated with the formulation at 5% (IGIV3I Grifols 5%).
15. Have conditions that might affect patient compliance.
16. Are unable to provide a storage serum sample just before the first dose of IGIV3I Grifols.
17. Are pregnant or nursing an infant child or unwilling to practice adequate birth control in 1-month period after the first infusion in the study.