Collaborative study for the establishment of the Ph. Eur. BRP batch 1 for anti-vaccinia immunoglobulin

Upon suggestion of the French Official Medicines Control Laboratory, a collaborative study was initiated by the European Directorate for the Quality of Medicines with the goal of calibrating the candidate European Pharmacopoeia biological reference preparation (Ph. Eur. BRP) for anti-vaccinia immunoglobulin batch 1 in International Units (IU) against the 1(st) British standard (anti-smallpox serum). The candidate BRP batch 1 was obtained by lyophilising a pool of four plasma samples obtained from one donor who was multi-vaccinated with smallpox vaccine (Lister strain) and who had relatively high titres of neutralising anti-vaccinia antibodies. The plasma complied with the requirements of the Ph. Eur. monograph Human plasma for fractionation. For the candidate BRP the precision of fill and the residual moisture after lyophilisation comply with the requirements for biological reference preparations. The stability of the material was shown to be satisfactory for the intended purpose in an accelerated degradation test. Eight laboratories participated in the study. Two samples had to be assayed (candidate BRP batch 1 and 1(st) British standard). All participants were requested to test the samples using a common method (plaque reduction neutralisation) that had been validated beforehand, and their own in-house anti-vaccinia immunoglobulin titration method. From the raw data returned, the potency of the candidate BRP was calculated in IU/ml using the parallel lines method. The precision (intra-assay variation), repeatability (intra-laboratory variation) and reproducibility (inter-laboratory variation) were assessed. All laboratories used the Lister strain of vaccinia virus for the plaque reduction neutralisation assay. For laboratories using cell-adapted vaccinia virus, the results were satisfactory regarding intra-assay variability, intra-laboratory variability and inter-laboratory variability. For laboratories using vaccinia virus produced on animals, results were less satisfactory. The study suggests that the candidate BRP batch 1 is suitable as a reference preparation for the potency assay of vaccinia immunoglobulin by the plaque reduction neutralisation method, using cell-adapted vaccinia virus. For this purpose, a potency of 23 IU/vial could be assigned to the candidate BRP. Based on the results of the stability testing, storage of the reference material at -20 degrees C and shipment on ice is recommended. Furthermore, it is recommended to monitor the potency of the reference material once per year. The candidate material was adopted as Ph. Eur. BRP at the Ph. Eur. Commission session in March 2005.