BAY 81-8973, a Full-Length Recombinant Factor VIII: Results from Assay Field Study

Background: BAY 81-8973 is a full-length unmodified recombinant factor VIII (rFVIII) in development for the treatment of hemophilia A. BAY 81-8973 has the same amino acid sequence as Bayer's sucrose-formulated rFVIII but is manufactured using the latest technologies. Potency labeling is based on the chromogenic assay. BAY 81-8973 has demonstrated an excellent safety and efficacy profile in the clinical development program. This field study was conducted to evaluate assay variability in BAY 81-8973 measurements compared with a marketed rFVIII (Advate^®, Baxter, Westlake Village, CA) using the methods, reference standards, and reagents typically used in clinical laboratories.

Methods: Clinical laboratories in North America, Europe, Israel, and South Africa were invited to participate in the study. Each laboratory was provided with 21 blinded samples to analyze using their routine assay (one-stage, chromogenic, or both), reagents, and standards. The 21 samples consisted of 3 aliquots each of spiked hemophilia plasma containing normal von Willebrand factor levels with BAY 81-8973 at 3 different levels: <10 IU/dL (low), 10-50 IU/dL (medium), >50 IU/dL (high); 3 aliquots each of spiked hemophilia plasma with Advate at the same levels (low, medium, high); and 3 aliquots of commercially available positive control sample (normal human plasma). Samples were identified by unique numbers and by target FVIII levels (low, medium, high). The nominal spiked target levels of FVIII concentration were 0.043 IU/mL (low), 0.375 IU/mL (medium), and 0.865 IU/mL (high) for BAY 81-8973 and Advate and 0.960 IU/mL for the plasma control. Results were analyzed statistically for intra- and interlaboratory variability.

Results: Of 82 laboratories contacted, 41 in 11 countries participated. Thirty-one laboratories used the one-stage assay only, 1 used the chromogenic assay only, and 9 used both assays. Intralaboratory variability was <11% for both assays at all FVIII levels and was similar for BAY 81-8973, Advate, and the plasma control. Interlaboratory variability was highest for the lowest concentration using the chromogenic assay (percent coefficient of variation: 60% for BAY 81-8973, 51% for Advate) and decreased to 14% for BAY 81-8973 (Advate, 12%; plasma control, 10%) with the one-stage assay and 5% (Advate, 6%; plasma control, 7%) with the chromogenic assay at the highest concentration. For the 9 laboratories that used both the one-stage and chromogenic assays, the chromogenic:one-stage ratio for mean values for BAY 81-8973 at low, medium, and high concentrations was 1.04, 1.04, and 1.14, respectively; for Advate, the ratios were 1.02, 1.07, and 1.21.

Conclusions: The laboratories participating in this field study used a wide range of methods and reagents for FVIII measurements. The variability of the results was similar for both BAY 81-8973 and Advate and highest for low concentrations. There was no relevant difference in the results between the one-stage and chromogenic assays.