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All reference extracts that are used to measure the potency of standardized products are skin tested. |
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Periodically the FDA selects a commercial lot of each standardized extract to serve as a new reference for verifying the bioequivalent potency of all other commercially available products of that species. These updated reference extracts are not skin tested but rather calibrated back to the previous reference using relative potency assays (e.g. ELISA inhibition). Early skin testing of these original reference extracts on a relatively small population of sensitive subjects was used to establish the bioequivalent unitage (e.g. BAU/ml, AU/ml) that we use today for each of the standardized products. |
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Standardized extracts from two different suppliers are going to be essentially the same. |
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The competition ELISA that is used to confirm bioequivalence for certain standardized products relies on the assumption that all major and minor allergens can be recognized by the total IgE from a donor serum pool. However, this assay may misrepresent the contribution of certain immunologically important allergens to an extract’s total potency. For example, the major allergens for house dust mite have been shown to vary as much as 15-fold when comparing identically labeled 10,000AU/ml dust mite extracts from two different suppliers. |
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Major Allergen values are not as clinically relevant as potency values (e.g. BAU or AU). |
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Major allergens are the predominant proteins that induce an IgE-mediated immune response in most patients and thus represent the immunologically active ingredients in an allergenic extract. In fact, the amount of major allergen for some extracts has been shown to correlate strongly with extract potency. The potency values for these extracts are determined using a bioassay that directly measures the content of major allergen (e.g. Fel d 1 for cat and Amb a 1 for short ragweed). Furthermore, several studies have even suggested the importance of specific major allergens in the course of allergic disease including the development of childhood asthma. |
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Standardized extracts will perform consistently in the clinic. |
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In the US, the relative potency of standardized extracts is measured using in vitro assays. What is important to remember is that the biochemical reactions being mea-sured in a surrogate potency assay may not necessarily mirror the complex biology of an IgE-mediated immune response in all humans. In other words, despite improve-ments in the consistency of extracts due to standardization, the relative potency of any extract may vary depending on the patient being diagnosed or treated. |