Estimate of maintenance EPO to darbepoetin alfa dose conversion ratio in a hospital-based dialysis patient population.

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.