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Abstract
Background:
Epoetin alfa (EPO) and darbepoetin alfa are erythropoiesis-stimulating agents (ESAs) used to treat anemia in patients with chronic kidney disease. EPO and darbepoetin alfa have a non-proportional dose conversion relationship across the dosing spectrum. However, reports comparing the dose relationship between the two ESAs do not adjust for the non-proportional dose relationship or for population differences. Because drug cost is directly related to dosage, appropriate methods to assess the dose relationship between the two ESAs are important to understand the economic implications of converting patient populations from one ESA treatment to another.
Objective:
To describe dose conversion methods that take into account the non-proportional dose relationship between EPO and darbepoetin alfa, and calculate the dose conversion ratio (DCR) between the two ESAs in a hospital-based dialysis patient population.
Methods:
This was a retrospective observational study where longitudinal data from medical charts were collected for chronic hemodialysis patients being treated at hospital-based dialysis centers. Mean maintenance DCRs were calculated at the population level for hemodialysis patients converted from EPO to darbepoetin alfa treatment and subsequently maintained on darbepoetin alfa. Two methods were used to determine the DCRs: a regression-based method using ordinary least squares regression, and ratio-based method using an arithmetic mean.
Results:
The estimated population mean maintenance DCR for the population in this analysis was 320:1 (Units EPO:µg darbepoetin alfa) using the regression-based method, and 350:1 using the ratio-based method. Sensitivity analysis yielded DCRs ranging from 311 to 333:1.
Conclusions:
The two methods in estimating the DCR presented here provide payers with an empirical way of comparing ESA utilization for pharmacoeconomic evaluation. DCR results may vary according to patient characteristics; however, mean DCRs of greater than 300:1 were obtained in this analysis. Exclusion of other patient-related factors that may influence ESA dose is a possible limitation of the study.
Transparency
Declaration of funding
This research was supported by Amgen Inc.
Declaration of financial/other relationships
A.S. has disclosed that he is a consultant for, and is on the speakers bureau for, AMAG, Watson Pharmaceuticals and Amgen. J.Y. has disclosed that he is a consultant for Takeda, Affymax, AMAG, Merck and Amgen; and is on the speakers bureau for Takeda, Merck, Genzyme, Otsuka and Amgen. He has also disclosed that he has received research funding from Fresenius Corp., North America; and holds stocks of Merck. S.R.G., I.K. and J.P. have disclosed that they are employees and stockholders of Amgen.
Acknowledgments
The authors thank Yeshi Mikyas, Amgen, for assistance in writing this manuscript and Santosh Sastry, Amgen, for his help with data access and SAS programming.
The results of this study were presented at the American Society of Health-System Pharmacists, Las Vegas, NV, USA, December 2009; and at the National Kidney Foundation Spring Clinical Meetings, Orlando, FL, USA, April 2010.