Officials with the U.S. Food and Drug Administration (FDA) officially confirmed the anemia drug Eprex's link to pure red cell aplasia (PRCA) in a letter published in this week's issue of The New England Journal of Medicine. Eprex's link to PRCA, a condition characterized by a near absence of red blood cell precursors, has been a concern in the medical community for months. Last fall, Johnson and Johnson, Eprex's maker, issued a warning letter to physicians concerning the potential for the side effect. In February, The New England Journal published a report regarding Eprex's link to an increase in PRCA cases. The FDA letter, which responded to the Journal's February report, cited 82 cases of PRCA in patient's taking Eprex.

Eprex is a man-made version of human erythropoietin (EPO). EPO is produced naturally in the body, mostly by the kidneys. It stimulates the bone marrow to produce red blood cells. If the body does not produce enough EPO, anemia can occur. This often occurs in people whose kidneys do not function properly. PRCA is estimated to affect less than one in 10,000 people.