- Stable rhEPO dose for rhEPO users: Group 2 subjects must be using the same rhEPO (epoetins or their biosimilars, or darbepoetin) with total weekly doses that varied by no more than 50% during the 4 weeks prior to Week -4. At Day 1 (randomization), confirm that total weekly doses varied by no more than 50% during the screening period.