Pilot Study of Rituximab for the Treatment of Acute Immune Thrombocytopenic Purpura (ITP)

Inclusion Criteria: * Non-splenectomized patients with acute ITP, where "acute ITP" is defined as a platelet count below 30 at the time that standard treatment was recommended by a physician and for which no treatment had been received for the preceding 30 days. * Must be receiving standard ITP treatment. Exclusion Criteria: * Cardiac arrhythmia. * Uncontrolled hypertension or inability to hold antihypertensive medications for 12 hours prior to and throughout study drug infusions. * Known coronary artery disease, angina pectoris or myocardial infarction within the last year. * Significant pulmonary disease within the last year. * Stroke, transient ischemic attack or venous thrombosis within the last year. * Secondary causes of thrombocytopenia (splenomegaly \[palpable spleen or radiologically confirmed \>14 cm\], drug-induced thrombocytopenia, hereditary thrombocytopenia, microangiopathic hemolytic anemia, myelodysplastic syndrome). * Chronic lymphocytic leukemia or lymphoma. * Active or metastatic cancer. * History of hepatitis B or C or HIV. * Active infection in the 4 weeks before randomization. * Inherited coagulation factor deficiency. * Aspirin, aspirin-containing compounds, salicylates, non-steroidal anti-inflammatory medications (NSAIDS) medications, clopidogrel or ticlopidine in the 7 days preceding study drug infusions; vitamin K antagonists (warfarin) in the 3 days preceding study drug infusions; unfractionated heparin or low molecular weight heparin in the 24 hours preceding study drug infusions. * Elevated INR or prolonged PTT; LDH, serum creatinine, liver function tests (AST/SGOT, ALT/SGPT, alkaline phosphatase, total bilirubin) increased more than 1.5 times upper limit of normal. * Prior rituximab treatment. * Unable to schedule 4 weekly study infusions. * Pregnancy or breastfeeding. * Known sensitivity to murine proteins, Chinese Hamster Ovary (CHO) cell proteins or to any component of rituximab. * Participation in another clinical trial. * Geographic inaccessibility. * Failure to provide written informed consent. * Any additional laboratory test result, health related illness or other diagnosis which, in the opinion of the treating physician, may put the subject's health or safety at risk.