Abstract: Objective To investigate the pharmacodynamics of long-acting erythropoietin (EPO) in mice and explore a proper method for an in vivo biological activity detection of long-acting EPO. Methods According to the reticulocyte assay method for determining the biological activity of EPO specified in the Chinese Pharmacopoeia, mice were subcutaneously injected with different doses of long-acting EPO or short-acting EPO. The percentage of reticulocytes in the mouse blood was observed for ten consecutive days after administration. A well-conceived dosing regimen and blood sampling schedule were designed to establish an in vivo method for determining the biological activity of long-acting EPO and to conduct the biological activity assay of long-acting EPO. Results According the bio-statistical model using the (3. 3) parallel line method, the in vivo biological activities of three batches of long-acting EPO were 94% (FL% 23%), 94% (FL% 17%) and 92% (FL% 15%) respectively when mice were given low, medium and high doses of 0.2, 0.4 and 0.8 IU per mouse, and day 4 was the optimal blood sampling time, as with short-acting EPO. Conclusion The blood-sampling time for in vivo biological activity assay of long-acting EPO is on day 4. A method should be established based on clinical dosage and product instructions and verified by tests on its applicability.

Key words: Long-Acting Erythropoietin, Reticulocyte Method, Biological Activity Assay, Blood Sampling Time, Mice