Primary Immune Thrombocytopenia

Posted by Graham McMahon • August 26th, 2011

In the latest article in our Clinical Therapeutics review series, a young woman with immune thrombocytopenia (ITP) who has been treated with a thrombopoietin-receptor agonist presents for advice regarding long-term treatment. The agents in this therapeutic class, romiplostim and eltrombopag, are effective in increasing platelet counts.      

Immune thrombocytopenia is a disorder that is characterized by immune-mediated platelet destruction and impaired platelet production resulting in a platelet count of less than 100,000 per cubic millimeter and varying degrees of bleeding risk.     

Clinical Pearls

 Does platelet count correlate with bleeding risk in patients with primary immune thrombocytopenia?   

Bleeding in immune thrombocytopenia is rare in patients who have a platelet count of more than 50,000 per cubic millimeter. The bleeding risk at lower platelet counts varies greatly from none to very severe, although spontaneous, life-threatening or fatal bleeding is generally confined to patients with a platelet count of less than 10,000 to 20,000 per cubic millimeter.   

 What is the initial approach to managing patients with primary immune thrombocytopenia?

Initial treatment for immune thrombocytopenia is generally a course of glucocorticoids, intravenous immune globulin, or both. The only second-line treatment that has been shown to produce sustained increases in the platelet count is splenectomy. Rituximab is widely used as a second-line agent, although the median duration of response with this agent is only 10.5 months.     

Figure 1. Structure of Romiplostim and Eltrombopag and the Cellular Mechanisms of Action.  

Morning Report Questions

     

Q: What is the efficacy of the thrombopoietin-receptor agonists, romiplostim?     

A: Romiplostim is administered subcutaneously once weekly. In an ongoing open-label extension study involving 292 patients treated with romiplostim, 94.5% achieved a platelet count of at least 50,000 per cubic millimeter during the study. 

Q: What is the efficacy of the thrombopoietin-receptor agonist, eltrombopag?     

A: Eltrombopag is given orally daily. In an ongoing open-label extension study involving 299 patients who completed a previous eltrombopag study, 87% of patients achieved a platelet count of at least 50,000 per cubic millimeter during treatment.

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