Rh Immune Globulin for ITP
Primary immune thrombocytopenia, formerly called idiopathic thrombocytopenic purpura (ITP), is an autoimmune disease that affects children and adults. Thrombocytopenia is caused by platelet autoantibodies. Treatment depends on clinical status, bleeding risk, and lifestyle of the patient. Treatment is usually not indicated for platelet counts higher than 50,000/uL in the absence of bleeding. Therapies include intravenous immunoglobulin (IVIG), corticosteroids, and intravenous Rh(D) immunoglobulin (IV RhIG).
Intravenous RhIg (WinRho SDF or Rhophylac) is FDA approved for treatment of acute and chronic ITP in Rh-positive pediatric and adult patients who have not been splenectomized. Administration of IV RhIG to an 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 large excess of antibody-coated red blood cells competes with antibody-coated platelets for clearance by the reticuloendothelial system, resulting in decreased phagocytosis of platelets and increased platelet count. This reticuloendothelial Fc receptor blockade has been referred to as a medical splenectomy.
Patients must be Rh positive and have not undergone splenectomy. They should not be IgA deficient and should not have any evidence of hemolytic anemia. WinRho contains a small amount of IgA and may cause severe allergic reactions in patients who are IgA deficient and have antibodies to IgA. Evaluation for preexisting hemolysis should include a complete blood count, reticulocyte count, direct antiglobulin test and urinalysis. Serum creatinine should also be checked, because of the risk of renal complications in patients who experience exacerbated hemolysis after treatment.
An initial dose of 50 to 75ug per kg of body weight is recommended unless the hemoglobin level is <10 g/dL. In this situation, a smaller dose of 25 to 40 ug per kg is indicated to reduce the risk of anemia. 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. WinRho is administered IV not IM. The entire dose should be given in a single IV injection over 3 to 5 minutes. After injection, patients should be monitored for at least 8 hours for adverse reactions. Hemoglobin level should be checked approximately 8 hours after injection.
A decrease in hemoglobin levels of 1 to 2 g/dL over the next 7 days is expected because passively administering anti-D to Rh positive patients results in extravascular hemolysis. FDA has required a black box warning on WinRho when used for treatment of ITP because 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 E, Fya and Jka 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.
Stotler BA and Schwartz J. How we use WinRho in patients with idiopathic thrombocytopenic purpura. Transfusion 2015;55:2547-2550.
