Thrombocytopenia
An abnormally low platelet count that increases bleeding risk. Immune thrombocytopenia (ITP) is an autoimmune condition where antibodies destroy platelets. Romiplostim is a peptide-Fc fusion protein that stimulates platelet production by activating the thrombopoietin receptor to treat chronic ITP.
Technical Context
Platelet count <150,000/μL; clinically significant bleeding risk at <50,000; spontaneous bleeding risk at <20,000; life-threatening risk at <10,000. Immune thrombocytopenia (ITP) pathophysiology: autoantibodies (primarily anti-GPIIb/IIIa and anti-GPIb/IX) → platelet opsonisation → Fc receptor-mediated splenic destruction AND megakaryocyte dysfunction → reduced platelet production. Romiplostim (Nplate) is a peptide-Fc fusion (AMG 531): two copies of a 14 amino acid peptide (with no sequence homology to endogenous thrombopoietin/TPO) bind and activate the TPO receptor (c-Mpl) on megakaryocytes → JAK2/STAT5 signalling → megakaryocyte proliferation and differentiation → increased platelet production. Romiplostim's Fc fusion design extends half-life through FcRn recycling. Dosing: weekly SC injection titrated to maintain platelet count ≥50,000/μL. Key safety concern: potential for bone marrow reticulin fibrosis with long-term use (monitored by CBC with peripheral smear).