New Drug of the day : Romiplostim

New Pharmacological Drug Classes Introduced in 2008 

Romiplostim is an fusion protein (peptibody) that contains two identical single-chain subunits, each consisting of a human immunoglobulin IgG1 Fc domain covalently linked to a peptide containing two TPO receptor-binding domains. 

The drug is licensed for the treatment of thrombocytopenia in patients with refractory chronic immune thrombocytopenic purpura and acts as a thrombopoietin (TPO) receptor agonist to activate intracellular transcriptional pathways leading to increased platelet production.

As a class, TPO receptor agonists are thought to increase the risk for development of bone marrow fibrosis and may increase the risk for hematologic malignancies. 

Romiplostim is administered as a subcutaneous injection with the dose adjusted to the lowest dose necessary to reduce the risk of bleeding and achieve a platelet count ≥50 x 109/L. A maximum weekly dose of 10 mcg/kg is recommended with therapy discontinued if the platelet count does not increase sufficiently within 4 weeks of therapy. Hyporesponsiveness or failure to maintain a platelet response may signal the development of neutralizing antibodies. 

Discontinuation of therapy poses a risk for worsening of thrombocytopenia below baseline, with subsequent hemorrhage. Patients receiving romiplostim must be monitored prior to initiation of therapy, frequently during treatment, and for 2 weeks following cessation of therapy.