Dose Dense Rituximab for High Risk Newly Diagnosed Acute Immune Thrombocytopenic Purpura

Inclusion Criteria: * Age: Subjects must be ≥ 1 year and ≤ 21 years of age. * Diagnosis: Patients must have newly diagnosed ITP and a platelet count of ≤ 20 x 109 per Liter. Bone marrow aspirate and biopsy should be performed to rule out malignancy in the bone marrow. * High-risk features : In addition, patients must have one of more of the following high-risk criteria: * Age ≥ 10 years * Grade II-IV bleeding at diagnosis * ANA positivity * No history of preceding infection within 2 weeks prior to ITP diagnosis * Performance Status: Patients must have a performance status ≥ 50%. Use Karnofsky for patients \> 16 years of age and Lansky for patients less than or equal to 16 years of age. See Appendix I for performance score. * Prior Therapy * Patients may not have received any treatment for ITP prior to start of therapy. * Patients may not receive systemic steroids ≥ 0.5 mg/kg prednisone (or equivalent) within 2 weeks prior to diagnosis. * Concomitant Medications Restrictions: * Steroids are only warranted as premedication prior to rituximab. * Patients who receive thrombopoetic agonists, eltrombopag or romiplostim will be taken off protocol. * Organ Function Requirements * Adequate Renal Function Defined As: estimated CrCl \> 60 mL/min or \>30% of GFR for age based on the Schwartz formula * Adequate Liver Function Defined As: AST and/or ALT less than 5 times the upper limit of normal, and/or direct bilirubin less than the 2 times of the upper limit of normal Exclusion Criteria * Patients with a history of Grade III-IV allergic reaction to rituximab * Patients with bone marrow neoplastic infiltration * Patients with a history of hepatitis B infection * Pregnancy and Breast Feeding * Female patients who are pregnant are ineligible (insert the reason: "due to risks of fetal and teratogenic adverse events as seen in animal/human studies" or "since there is yet no available information regarding human fetal or teratogenic toxicities"). * Lactating females are not eligible unless they have agreed not to breastfeed their infants. * Female patients of childbearing potential are not eligible unless a negative pregnancy test result has been obtained.