Importance of biologic follow-ons: experience with EPO.

The importance of recombinant human erythropoietin (epoetin) therapy has been clearly demonstrated in patients with anemia due to chronic kidney disease. The use of biopharmaceuticals to replace endogenous proteins, which may be inadequately low, carries the risk of stimulating the immune system to develop autoantibodies. Although these proteins are designed to closely mimic the endogenous proteins, they may have potential immunogenic properties. Erythropoietin produced by recombinant DNA technology is the most successful and efficacious agent for treating anemia. It was initially used in treating anemia in chronic kidney disease patients. Pure red cell aplasia (PRCA) ensuing from production of neutralizing anti-erythropoietin antibodies occurred very rarely with epoetin treatment. This agent was initially administered intravenously, but the mode of administration was progressively altered to subcutaneous without apparent increase in immune reaction. However, between 1998 and 2001, a sharp increase in the number of PRCA cases was seen. PRCA had been a very rare complication until this time. All of these patients had high affinity neutralizing anti-erythropoietin antibodies. This observation was made primarily in cases where one brand of epoetin, Eprex, was administered subcutaneously to patients with chronic kidney disease treated outside the United States, although a small number of cases among chronic kidney disease patients treated solely with epoetin beta were also identified. The marked increase in the number of Eprex cases was attributed to a change in the stabilizers, storage, and route of administration of Eprex to patients with chronic kidney disease. Since then changes have been made to the route of administration, storage, and handling of Eprex, and more recently to the rubber stoppers used in the prefilled syringes. Eprex was administered intravenously to chronic kidney disease patients and, with improved storage and handling, there was a subsequent dramatic reduction in the number of cases. More recently, the rubber stoppers have been replaced by Teflon-coated ones to prevent interactions with stabilizers and release of chemicals that have adjuvant properties. However, this concern is still relevant in the new generation of epoetin agents and generic formulations of epoetins. Epoetin treatment for anemia requires regular follow-up of hemoglobin levels but also of reticulocyte counts in chronic kidney disease patients.