We read with interest the cost-effectiveness analysis by Del Rio et al.,1 which compared epoetin alpha and darbepoetin alfa therapy for anemia in patients receiving pegylated interferon and ribavirin combination therapy for HCV. The authors concluded that use of darbepoetin alfa is cost-effective because the cost of darbepoetin per additional quality-adjusted life-year (QALY) was below a cost per QALY threshold of $50,000, whereas epoetin alfa was above the threshold value. We believe this conclusion was incorrect because of a major calculation error in the costs of erythropoietic treatments made by the authors.
The authors report calculating the weekly drug costs for epoetin ($596.50) and darbepoetin ($278.44) based on the average wholesale prices (AWP) published in the 2005 Red Book for the base case analysis (table 4 in Del Rio et al.). However, a correct calculation would have nearly doubled the darbepoetin weekly costs and resulted in comparable weekly drug costs between epoetin and darbepoetin, drastically changing the authors' conclusions.
The doses of growth factors used in the model were 40,000 Units epoetin once a week and 3.0 μg/kg body weight darbepoetin once every 2 weeks (∼200 μg for a 70-kg patient, or about 100 μg weekly; see page 1600 in Del Rio et al.1). The published Red Book AWP prices in 20052 are $572.64 per one 40,000 Unit vial for epoetin alfa, and $1025.28 per one 200 μg vial for darbepoetin alfa. Therefore, weekly doses of 40,000 Units epoetin and 100 μg darbepoetin valued at the 2005 AWP translate into weekly drug costs of $572.64 and $512.64, respectively. The weekly costs for these selected regimens are actually much more comparable than the 2-fold difference reported by the authors. Using the correct weekly darbepoetin alfa cost in the base case of the authors' model, the incremental cost-effectiveness ratios for darbepoetin and epoetin should become very similar, and may both be above the $50,000 threshold.