TPO and Thrombocytopenia: Although it is believed that romiplostim has lower affinity than native Tpo, it produces an immediate activation cascade starting with phosphorylation of the receptor and initiation of the JAK2 and STAT5 pathways stimulating CFU-Mk growth and increased megakaryocyte ploidy in a dose-dependent fashion.116 It was approved by the FDA in 2008 for ITP and administered weekly as a subcutaneous injection at a dose of 1 to 10 mcg/kg and also approved for patients with radiation injury-related thrombocytopenia.