Comparison of coagulant activity of factor VII and activated factor VII activity assays when used for determination of recombinant activated factor VII levels in plasma.
Two assays [coagulant activity of factor VII (FVII:C) and activated factor VII (FVIIa) activity] are currently available for the assessment of factor VII and FVIIa pharmacokinetics. This article presents the results of a comparison of the two assays when applied both in vitro as well as during clinical pharmacokinetic trials of recombinant FVIIa (rFVIIa) administered to healthy individuals and haemophilia patients. The in-vitro data showed that, for the FVII:C assay, plasma samples do not dilute in parallel. For the FVIIa activity assay, dilutions of samples are both parallel and linear with different dilutions of the calibrator. Moreover, intra-assay variation was found to be smaller for the FVIIa activity assay than for the FVII:C assay. When adding different amounts of rFVIIa (0-6 microg/ml) to normal plasma, a mean specific activity of rFVIIa of 48.6 U/mug was observed on applying the FVII:C assay; however, the specific activity decreased with increasing levels of rFVIIa. For the FVIIa activity assay, the mean specific activity was 45.4 IU/mug. Direct comparison of the two activity assays showed that no simple conversion between FVII:C and FVIIa activity measurements are possible. When applying the two assays for pharmacokinetic assessments in two clinical trials, statistically significant different estimates for the area under the curve, half-life, clearance and volume of distribution were obtained. In conclusion, for evaluation of rFVIIa pharmacokinetic properties, activity should be measured with the FVIIa activity assay - which is a more specific and reliable assay of the two available factor VII activity assays, especially when assessing low activity levels.
Scharling
Birgitte
B
Novo Nordisk A/S, Bagsvaerd, Denmark. Bish@novonordisk.com
Nielsen
Gert G
GG
Klitgaard
Thomas
T
Skovsted
Thor Aa
TA
Møss
Judi
J
Segel
Stine
S
Larsen
Lone Frost
LF
D000293:Adolescent; D000328:Adult; D001777:Blood Coagulation / Q000187:drug effects / Q000502:physiology; D001780:Blood Coagulation Tests / Q000379:methods*; D002648:Child; D002675:Child, Preschool; D003029:Coagulants / Q000378:metabolism; D005167:Factor VII / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D005168:Factor VII Deficiency / Q000097:blood* / Q000188:drug therapy*; D015942:Factor VIIa; D006467:Hemophilia A / Q000188:drug therapy / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D010949:Plasma / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000097:blood / Q000737:chemistry / Q000494:pharmacology; D012016:Reference Values; D013925:Thromboplastin / Q000378:metabolism
D003029:Coagulants; D011994:Recombinant Proteins; D005167:Factor VII; D013925:Thromboplastin; C103587:recombinant FVIIa; D015942:Factor VIIa