Pharmacokinetics of Recombinant Factor VIIa in the Rat – A Comparison of Bio-, Immuno- and Isotope Assays

Recombinant human factor VIIa (rFVIIa) is an activated coagulation factor for intravenous use as a haemostatic agent in haemophiliacs who generate antibodies against factor VIII or IX. Plasma kinetic studies are important for the understanding of the action of rFVIIa which is exerted in the vascular compartment of the body, more specifically on the vessel walls at the site of injury. In the present study, rats were dosed 100 or 500 μg/kg 125 I-rFVIIa i.v., without any side effects being observed, and the plasma profile of rFVIIa was studied by 3 different assays that were shown to correlate well at early times post-dose: trichloroacetic acid (TCA)-precipitable drug-related radioactivity, rFVIIa antigen determination by ELISA technique, and the assay of clot activity which is the only clinically applicable assay