What is the practical conversion dose when changing from epoetin alfa to darbepoetin outside of clinical trials?

BACKGROUND

The recommended conversion dose for changing from epoetin alfa to darbepoetin alfa is 200 units to 1 microg. However, this may result in the over treatment of uraemic anaemia.

METHODS

All in-centre haemodialysis patients (n = 60) were converted from an existing subcutaneous epoetin alfa regimen to weekly intravenous darbepoetin alfa. The protocol for anaemia management included a target haemoglobin (Hb) concentration of 120-130 g/L and a ferritin of 300-600 microg/L. Patient treatments were converted from subcutaneous epoetin alfa to weekly, intravenous darbepoetin alfa at month 0, at a conversion dose of 200 units epoetin alfa to 1 microg darbepoetin.

RESULTS

Both Hb and ferritin concentrations remained within the target range, but darbepoetin dosages fell from 50.8 to 42.3 microg/week by month 3 (P = 0.02). The initial conversion factor of 210 units/microg rose to 275 units/microg (P = 0.01) at month 4. No difference in conversion dosage could be determined between patients who were epoetin sensitive (<200 units/kg per week) or resistant (>200 units/kg per week, P = NS). Patients were then switched to fortnightly darbepoetin alfa dosing treatments; the existing weekly dose being doubled and Hb levels fell from 125 to 110 g/L (P < 0.0001), despite an increase in the mean dose from 44.9 to 47.5 microg/week (P = 0.02).

CONCLUSION

The original dosage reduction after the switch from epoetin alfa to weekly intravenous darbepoetin alfa may offset the increased relative cost of the latter. When administered weekly and intravenously, darbepoetin alfa maintains Hb at a more favourable conversion rate than is currently recommended.