Objective To study the pharmacokinetics of a novel recombinant human granulocyte colonystimulating factor (rhG-CSFa) in rats and to determine the proteolytic rates of rhG-CSFa in the whole blood and serum of rats in vitro. Methods The pharmacokinetics of rhG-CSFa and conventional (wild type

WT) granulocyte colonystimulating factor (G-CSF) were investigated in Sprague-Dawley rats which received either intravenous or subcutaneous injection of rhG-CSFa or WT G-CSF at three different doses (20

50

or 100 μg/kg). The blood samples of rats were collected at multiple time points (from 0.08 to 12 h) and the concentrations of rhG-CSFa and WT G-CSF in serum were determined with a sandwich enzyme-linked immunosorbent assay (ELISA). For the study of proteolytic rates in vitro

the concentrations of rhG-CSFa or WT G-CSF were determined at 3-minute intervals after addition of the respective drug to rat’s whole blood or serum. Results Pharmacokinetic analysis of serum rhG-CSFa or WT G-CSF levels indicated that

at each dose tested

for either route of drug administration

the area under concentration-time curve values and the maximum serum concentration of rhG-CSFa were higher than those of WT G-CSF

and the serum half life of rhG-CSFa was longer than that of WT G-CSF. Subsequent in vitro whole blood and serum stability study showed that the rates of drug degradation in WT G-CSF were 1.8 folds and 1.5 folds higher than those in rhG-CSFa

respectively. Conclusion rhG-CSFa has better serum and whole blood stability in vitro and higher bioavailability in vivo as compared to WT G-CSF.