Thrombopoietin Receptor Agonists for Thrombocytopenia

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Both romiplostim and eltrombopag are approved for the treatment of thrombocytopenia in patients with chronic immune (idiopathic) thrombocytopenic purpura (ITP). The FDA approved both treatments in 2008 for patients with thrombocytopenia following an insufficient response to corticosteroids, immunoglobulins, or splenectomy. Treatment with eltrombopag 50 mg improved platelet counts by ≥ 50,000/mcL for 60% to 70% of patients enrolled across two clinical trials. Similarly, platelet counts were improved by ≥ 50,000/mcL in 60% of patients treated with romiplostim.

Romiplostim and eltrombopag are receptor agonists that mimic the effects of thrombopoietin on megakaryocytes and increase platelet production, explains Keith McCrae, MD. While both agents interact with the thrombopoietin receptor, they differ structurally and chemically from each other. Their toxicity profiles are similar, although eltrombopag has an additional toxicity of elevating liver function tests in some individuals.

There are differences in the way each medication is administered, Ivy Altomare, MD, notes. Romiplostim is given as a once-weekly subcutaneous injection that is titrated according to platelet counts whereas eltrombopag is an oral drug that can be taken at home and is slightly easier to titrate, since 3 established doses levels are available. Both medications are thought to be maintenance treatments, and responses appear to continue for as long as the drug is administered, Altomare suggests.

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