Pharmacokinetics, tissue distribution and excretion of 40 kDa PEG and PEGylated rFVIII (N8-GP) in rats

The biologic fate of the [3H]PEG-moiety incorporated into N8-GP was evaluated based on single i.v. bolus doses to rats. Furthermore, the 40 kDa [3H]PEG-moiety was given separately to rats by single i.v. bolus doses, to investigate if the pharmacokinetics were dose-dependent. For both compounds, plasma pharmacokinetics, distribution and excretion pathways were investigated, based on total radioactivity measurements ([3H]N8-GP: 0.17-4.1 mg/kg;~1300-30,000 U/kg, PEG load of ~ 0.03-0.7 mg/kg); ([3H]PEG: 0.6, 1, 12, 100 and 200 mg/kg). The plasma concentration of the intact N8-GP conjugate was also measured by ELISA. After single i.v. administration to rats, both [3H]N8-GP and [3H]PEG were shown to be widely distributed, mainly in highly vascularized tissues, with the lowest levels of radioactivity found in the CNS. Though a slow elimination of radioactivity was observed over the 12-week study period, approximately half of the radioactive dose of either compound was removed from the body 1 week post-dose. The radioactivity was eliminated mainly via the kidney into urine but also via the liver into feces, with a larger fraction found in the feces for [3H]N8-GP. Elimination of the 40 kDa PEG-moiety was shown to be dose-dependent with faster elimination at lower dose levels. The clinical dose of N8-GP provides a substantially lower PEG exposure (50-75 U/kg; PEG load of < 0.002 mg/kg) when compared to the PEG doses investigated in this paper (0.03-200 mg/kg). This may imply an even faster clearance of the PEG-moiety after N8-GP administration of clinically relevant doses.

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