Quantitative assessment of minimal effective concentration of erythropoiesis-stimulating agents

Minimal effective concentration (MEC) was proposed to explain why subcutaneous (SC) administration of erythropoietin (EPO) induces a higher hemoglobin (HGB) increase than intravenous (IV) administration. It has been further used to explain the paradox that erythropoiesis-stimulating agent (ESA) with lower receptor binding affinity may have higher in vivo activity. We have developed a pharmacokinetic and pharmacodynamic (PK/PD) model with incorporation of the operational model of agonism to characterize the data from two clinical trials. By using model-based simulations, we demonstrate that SC route is more efficacious than IV route and explain the paradoxical behavior of ESAs. We determined that MEC can be quantified by C50, which represents the concentration of an ESA producing its half-maximal effect of stimulating the proliferation of erythroid precursor cells. The model used may allow joint PK/PD modeling of data from different ESAs, and provide a platform for dosing regimen optimizations and future clinical study designs.