Erythropoietins: a common mechanism of action.

Clinical development of erythropoiesis-stimulating agents (ESAs) revolutionized the management of anemia. The major clinical benefits of ESAs are effective treatment of anemia and avoidance of blood transfusion risks. Erythropoietin (EPO) interacts directly with the EPO receptor on the red blood cell (RBC) surface, triggering activation of several signal transduction pathways, resulting in the proliferation and terminal differentiation of erythroid precursor cells and providing protection from RBC precursor apoptosis. The magnitude of increase in RBC concentration in response to administration of recombinant human EPO products (rhEPO) is primarily controlled by the length of time EPO concentrations are maintained, not by the EPO concentration level. Subcutaneous (SC) EPO administration results in slower absorption than intravenous (IV) administration, leading to lower peak plasma levels and an apparent extended terminal half-life. However, SC administration requires additional needle-sticks and is associated with an increased risk of immunogenicity compared with IV administration. Multiple pathways may play a role in EPO clearance from the body. Epoetin alfa was the first rhEPO produced and approved for pharmaceutical use, followed by several related products and by newer ESAs with the same mechanism but more prolonged action. Darbepoetin alfa is a hyperglycosylated EPO analog with an extended terminal half-life and a greater relative potency compared with rhEPO at extended dosing intervals. PEGylation of EPO (addition of polyethylene glycol) has been used to further extend the terminal half-life. Also, new strategies are under investigation for stimulating erythropoiesis through activation of the EPO receptor.