Calibration of human coagulation factor VII concentrate Ph. Eur. BRP batch 2

The potency assay of human coagulation factor VII concentrate preparations as described in the European Pharmacopoeia (Ph. Eur.) requires a reference preparation calibrated in International Units (IU). The current Ph. Eur. Biological Reference Preparation (BRP) batch 1 was established in 2005 during an international collaborative study. It has an assigned potency of 8.2 IU/vial for the chromogenic assay method. Stocks of this BRP are dwindling and a replacement batch needs to be established. A candidate material was produced by a manufacturer from a plasma-derived concentrate preparation, with the same formulation and approximately the same potency, in the interest of continuity. The candidate material fulfilled the requirements of a BRP with regard to precision and homogeneity of fill, residual water content and stability. The potency of the candidate BRP (cBRP) was determined using chromogenic assays as required by the Ph. Eur. and in-house clotting assays in an attempt to assign a potency for both methods, as is the case for the current batch. The statistical model used for most laboratories was the maximum likelihood of the parallel line model using a logarithmic transformation of the responses. In the chromogenic assay, a potency of 9.9 IU/vial (+/- 1.8 %) was obtained for the cBRP with a very good consistency between laboratories. The results from the clotting assay, however, were less homogenous and yielded consistently higher results (13 IU/vial +/- 12 %), probably due to a higher activated factor VII (FVIIa) content than in the current BRP (3 % as compared to 0.3 %). Due to the large difference between the values obtained with the 2 different methods, it was not possible to reconcile the outcomes with each other. On the other hand, the uncertainty observed with the clotting assay method was quite large and seemed questionable for a reference preparation. Therefore the use of BRP batch 2 as a reference for the clotting assay method is not recommended. Nevertheless, the results of the study showed that the candidate BRP (cBRP) is suitable as a reference standard for the chromogenic assay according to the Ph. Eur. general chapter 2.7.10 Assay of human coagulation factor VII. It was adopted by the Ph. Eur. Commission in December 2009 as an official Ph. Eur. BRP for human coagulation factor VII concentrate with an assigned potency of 9.9 IU/vial.