49 Intravenous RhIg (WinRho SDF or Rhophylac) is effective in some patients with immune thrombocytopenia (ITP) including:
Children with acute or chronic ITP
Adults with chronic ITP
Children and adults with HIV-related ITP
Administration of IV RhIG to a Rh positive patient results in the binding of anti-D antibody to the patients’ red blood cells. In a thrombocytopenic patient, there are approximately 500 antibody-coated red cells for every antibody-coated platelet. The reticuloendothelial system phagocytizes red cells instead of platelets, allowing the platelet count to increase. This reticuloendothelial Fc receptor blockade has been referred to as a medical splenectomy. Patients must be Rh positive and have not undergone splenectomy. An initial dose of 250 IU (50 ug) per kg of body weight is recommended unless the hemoglobin level is <10 g/dL. In this situation, a smaller dose of 125 to 200 IU (25 to 40 ug) per kg is indicated. The initial dose can be administered at one time or divided into 2 doses given on separate days. Additional doses of 125 to 300 IU/kg can be given as needed. A decrease in hemoglobin levels up to 1.7 g/dL is expected because passively administered anti-D attaches to the D antigen on the patient’s RBCs and shortens their life span. Some patients experience more severe intravascular hemolysis, which may be life threatening. If a patient needs to be transfused, Rh negative red blood cells should be given to prevent further exacerbation of hemolysis. Patients treated with IV RhIG will develop a positive direct antiglobulin test and a positive antibody screen. In addition to anti-D, passively acquired anti-D, C and E antibodies may be detected. If IV RhIg is not available, ITP can be treated with intramuscular RhIg (RhoGam). Doses of 13 ug/kg can be given weekly. One to two days after treatment, the platelet count should rise to approximately 50,000/uL and gradually peak at 7-14 days.
