BIOPOTENCY ASSAYS: QUALITY ATTRIBUTES: ALTERNATE ZONE UNIFORMITY (AZU)

Uniformity of zones (AZU) is an important factor contributing to assay accuracy. Variable zones resulting from variation in lawn density, variance in cylinder fill volumes, temperature of incubation etc. can take an assay into a possible error zone. The 21-CFR/ USP assay has a built in sub routine to correct for sample zone variance based on its adjacent reference zone (RF) i.e., relative to the cumulative average of all the standard midpoint (RF) values. An important consideration is that as the distance increases between sample and its corresponding RF zone, the effectiveness of this correction becomes diminished (especially true for points A and B of the standard). Accordingly, our approach has always opted for RF zones within a range of at least 18 mm. Correction for zone variance is more effective among zones that are in closer proximity. When running bioassays, a better approach is to aim for elimination of zone variance altogether and limit the reliance on corrections. This is possible by using newer technology applicable to each segment of the assay. During the reading process, our site, monitors zone uniformity to assure adherence to pre-specified restrictions in variability.