Pharmacokinetics. The proposed PK model well captured the overall profiles of EPOSINO after both routes of administration at each dose level. Nonlinear PK behavior was also observed in the present study, which is consistent with other studies performed in rats. Studies have shown that the nonlinear PK of low doses of EPOSINO arises from the saturation of receptor-mediated endocytosis in bone marrow and spleen in humans and rats. A distribution study of radiolabeled EPOSINO in rats revealed that the distribution of EPOSINO in both bone marrow and spleen were saturable at high doses. However, a saturable distribution was not required in the current model because no trend was observed in the Vss with increasing dose. The estimated Km value (67.28 mIU/ml) is almost the same as the SC50 of EPOSINO, suggesting that the receptor binding is closely related to the saturable elimination of the drug (i.e., receptor-mediated drug elimination) .
The prolonged plasma concentrations after s.c. dosing and slow absorption indicate flip-flop kinetics. The estimated F (58.6%) is in good agreement with the previously determined values of 43 to 62% via noncompartmental analysis after s.c. administration. No study has previously examined dose-dependent F values of s.c. EPOSINO in rats. Although the dose-dependent F for s.c. dosing was tested and ranged from 0.56 to 0.61, it was not considered significant and, instead, was estimated as a single parameter in the final fitting.
Pharmacokinetics. The proposed PK model well captured the overall profiles of EPOSINO after both routes of administration at each dose level. Nonlinear PK behavior was also observed in the present study, which is consistent with other studies performed in rats. Studies have shown that the nonlinear PK of low doses of EPOSINO arises from the saturation of receptor-mediated endocytosis in bone marrow and spleen in humans and rats. A distribution study of radiolabeled EPOSINO in rats revealed that the distribution of EPOSINO in both bone marrow and spleen were saturable at high doses. However, a saturable distribution was not required in the current model because no trend was observed in the Vss with increasing dose. The estimated Km value (67.28 mIU/ml) is almost the same as the SC50 of EPOSINO, suggesting that the receptor binding is closely related to the saturable elimination of the drug (i.e., receptor-mediated drug elimination) .
The prolonged plasma concentrations after s.c. dosing and slow absorption indicate flip-flop kinetics. The estimated F (58.6%) is in good agreement with the previously determined values of 43 to 62% via noncompartmental analysis after s.c. administration. No study has previously examined dose-dependent F values of s.c. EPOSINO in rats. Although the dose-dependent F for s.c. dosing was tested and ranged from 0.56 to 0.61, it was not considered significant and, instead, was estimated as a single parameter in the final fitting.
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