BACKGROUND: Darbepoetin alfa (Aranesp; Amgen, Thousand Oaks, CA) is a new erythropoiesis-stimulating protein with a threefold longer terminal half-life than recombinant human erythropoietin (epoetin) in patients with chronic kidney disease (CKD). The purpose of this randomized, double-blind, noninferiority study is to determine whether darbepoetin alfa is as effective as epoetin for the treatment of anemia in hemodialysis patients when administered at a reduced dosing frequency. METHODS: Patients receiving epoetin therapy were randomized to continue epoetin administered intravenously (IV) three times weekly (n = 338) or change to darbepoetin alfa administered IV once weekly (n = 169). The dose of darbepoetin alfa or epoetin was individually titrated to maintain hemoglobin concentrations within -1.0 to +1.5 g/dL (-10 to +15 g/L) of patients' baseline values and within a range of 9.0 to 13.0 g/dL (90 to 130 g/L) for up to 28 weeks (20-week dose-titration period followed by an 8-week evaluation period). The primary end point was change in hemoglobin level between baseline and the evaluation period (weeks 21 to 28). RESULTS: Mean changes in hemoglobin levels from baseline to the evaluation period were 0.24 +/- 0.10 (SE) g/dL (2.4 +/- 1.0 g/L) in the darbepoetin alfa group and 0.11 +/- 0.07 g/dL (1.1 +/- 0.7 g/L) in the epoetin group, a difference of 0.13 g/dL (95% confidence interval [CI], -0.08 +/- 0.33 [1.3 g/L; 95% CI, -0.8 to 3.3]). This difference was not statistically significant or clinically relevant despite the reduced frequency of darbepoetin alfa administration. The safety profile of darbepoetin alfa was similar to that of epoetin, and no antibody formation to either treatment was detected. CONCLUSION: These results show that darbepoetin alfa maintains hemoglobin concentrations as effectively and safely as epoetin in patients with CKD, but with a reduced dosing frequency. Copyright 2002 by the National Kidney Foundation, Inc.