Managed Care - October 2008 - (Page 49) TOMORROW’S MEDICINE Platelet Production Bolstered With Romiplostim Approval A peptide fusion protein can stem the tide of abnormal, excessive bleeding Thomas Morrow, MD P latelets are amazing components of our bloodstream. Not actually cells (they lack a nucleus and major metabolic machinery) and available in large quantities, they respond in a moment’s notice to a leak in our blood vessels to prevent catastrophic bleeding. A normal platelet count has a rather wide range — from 150,000 to 450,000 platelets per microliter of blood. They are also very effective at preventing bleeding, as just a small part (10,000) of the normal amount will prevent bleeding in most people. Most of the time, people do not even know platelets are around, but occasionally an abnormality of platelets places a person at high risk for medical complications. One abnormality is a disorder called idiopathic thrombocytopenia purpura or ITP. The name describes the disorder — idiopathic for unknown cause, thrombocytopenia for low platelet count, and purpura for bruised skin. Two forms: acute and chronic The acute form often follows a viral infection and occurs in children. This form typically lasts about 6 to 12 months, often resolves spontaneously, typically does not return, and may not even require treatment. About 5 percent of children may require therapy if the condition does not resolve spontaneously. Chronic ITP has a variable presentation and its course can last for decades. It is known to be an autoimmune disease that marks platelets to be destroyed by the spleen, but the trigger is unknown. With time, most people suffering from chronic ITP are able to cease active treatment and keep a safe platelet count. Thomas Morrow, MD, is the immediate past president of the National Association of Managed Care Physicians. He has 23 years of managed care experience at the payer or health plan level. Treatment of chronic ITP depends upon the symptoms and platelet count. As long as the platelet count remains high and no bleeding occurs, there is no need to treat. If the count drops to low levels or if signs of bleeding occur, treatment is rendered. Types of bleeding include excessive bruising, prolonged bleeding from skin injuries, spontaneous bleeding from gums or nose, blood in the urine or stools, and unusually heavy menses in women. The diagnosis of ITP is based upon excluding other causes of bleeding and the low platelet count. The low count can be from another infection, other bone marrow disorders, or medication side effects. Tests that are typical of the workup for ITP include a complete blood count (CBC), blood smear, and bone marrow biopsy with microscopic examination. Once these tests exclude other causes of thrombocytopenia, ITP can be considered. Therapeutic approaches include immune system modulation with corticosteroids and intravenous immunoglobulin or surgical removal of the spleen to prevent platelet destruction. In an emergency, transfusions of platelets may be used, but due to the very short lifespan of a platelet, this therapy is not feasible for long-term use. Romiplostim In late August, the FDA announced approval of a new approach to treating ITP, romiplostim (Nplate). Romiplostim is an Fc-peptide fusion protein (also called a peptibody) that activates intracellular transcriptional pathways leading to increased platelet production via the TPO receptor. The peptibody molecule contains two single chain component subunits linked to the constant domains of antibodies. It does not contain OCTOBER 2008 / MANAGED CARE 49
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