A Study to Find How Safe and Effective GAMMAPLEX® is in Subjects With Chronic Idiopathic Thrombocytopenic Purpura (ITP)

Inclusion Criteria: 1. Males and females aged between 18 and 70 years. 2. Confirmed diagnosis of chronic ITP of at least 6 months duration. 3. Platelet count of less than or equal to 20 x 10 9/L at enrollment. 4. Absence of other conditions that, in the opinion of the investigator, could cause thrombocytopenia. 5. If subjects were treated with corticosteroids the treatment regimen/dose must have been stable (for a minimum of 2 weeks before screening). The dose of corticosteriod or other immunosuppressant should have remained constant until Day 32. 6) If subjects were being treated with cyclophosphamide, azathioprine or attenuated androgens, the treatment regimen and dose must have been stable for a minimum of 2 months before Day 1. The dose of corticosteriod or other immunosuppressant should have remained constant until Day 32. 7) Splenectomized subjects and both Rh(D)+ and Rh(D)- subjects may be included. 8\) The subject has signed an informed consent form (subjects must be at least 18 years old), and/or the subject's legal guardian has signed the informed consent form if indicated 9) If a subject is a female of child-bearing potential, she must have a negative result on a urine-based HCG pregnancy test. 10\) If a subject is a female who is or becomes sexually active, she must practice contraception by using a method of proven reliability for the duration of the study. Exclusion Criteria: 1. A history of any severe or anaphylactic reaction to blood or any blood-derived product, or any severe reaction to IGIV or any other IgG preparation. 2. Intolerance to any component of the investigational product. 3. Received any live virus vaccine within the last 3 months prior to Day1. 4. Received an IGIV preparation within 1 month prior to Day 1. 5. Were currently receiving, or has received, any investigational agent within the 1 month prior to Day 1. 6. Received any blood, blood product, or blood derivative within the 1 month prior to Day 1. 7. Received Rituximab within the 3 months before Day 1. 8. Pregnant or nursing. 9. Tested positive for any of the following at screening: HBsAg, NAT for HCV, NAT for HIV, Antibodies to HCV or HIV 1 or 2. 10. Had levels greater than 2.5 times the upper limit of normal at screening, as defined by the central laboratory, of alanine aminotransferase or aspartate aminotransferase. 11. Had severe renal impairment (defined as serum creatinine greater than 2 times the upper limit of normal or BUN greater than 2.5 times the upper limit of normal for the range of the laboratory doing the analysis); on dialysis; a history of acute renal failure. 12. Known to have abused alcohol, opiates, psychotropic agents, or other chemicals or drugs within the past 12 months. 13. History of deep vein thrombosis (DVT) or thrombotic complications of IGIV therapy. 14. Any history or sign of hyperviscosity, transient ischemic attack (TIA), stroke, other thromboembolic event, or unstable angina. 15. Suffered from any acute or chronic medical conditions (e.g., renal disease or predisposing conditions for renal disease, coronary artery disease, or protein losing enteropathy) that, in the opinion of the investigator, may interfere with the conduct of the study. 16. An acquired medical condition, such as chronic lymphocytic leukemia, lymphoma, multiple myeloma, chronic or recurrent neutropenia (defined as an absolute neutrophil count (ANC) \< 1 x 109/L). 17. Non-controlled arterial hypertension (systolic blood pressure \>160 mmHg and/or diastolic blood pressure \>90 mmHg). 18. Anemic (hemoglobin \<10 g/dL) at screening. 19. Unlikely to adhere to the protocol requirements of the study or is likely to be uncooperative.