OBJECTIVES: To evaluate evolving epoetin alfa (EPO) and darbepoetin alfa (DARB) dosing patterns from 2002–2004 in patients with pre-dialysis chronic kidney disease (CKD) receiving care in nephrology clinics. METHODS: A random panel of approximately 250 nephrologists was requested bimonthly to review the medical records of their last two anemic pre-dialysis CKD patients seen currently receiving an erythropoiesis-stimulating therapy (EST). Data on patient demographics, co-morbid conditions, CKD status, EST dose, and frequency of administration were collected every two months to evaluate changes over time. RESULTS: A yotal of 1585 patient charts were reviewed from November, 2002 to May, 2004 (EPO: 1047; DARB: 538). Patient demographics, comorbid conditions, baseline hemoglobin, and renal function were similar between groups. Weekly and extended (> Q2W) dosing patterns were seen in both groups (May, 2004 – EPO: QW, 62%; Q2W, 24%; Other, 14%; DARB: QW, 32%; Q2W, 51%; Other, 19%). A decrease in the dose only ratio (units EPO: mcg DARB) from 276:1 in November, 2002 (average weekly dose – EPO: 10,481 units; DARB: 38 mcg) to 217:1 (average weighted weekly dose – EPO: 9,981 units; DARB: 46 mcg) in May, 2004 was observed. The average weekly dose over the course of the study (EPO: 10,172 units; DARB: 41 mcg) corresponded to weekly costs of $113 and $164 for EPO and DARB (based on 2003 wholesale acquisition cost), respectively. CONCLUSIONS: Increasing DARB doses have been seen from November, 2002 through May, 2004, resulting in a lower dose only conversion ratio and greater average weekly drug costs compared to EPO. These analyses will assist clinicians and formulary decision makers in identifying real-world equivalent dosing and subsequent cost of treatment of these agents.