Stability of allergen extracts used in skin testing and immunotherapy

Purpose of review The present article reviews allergen extract stability applied to US manufactured products. Methods used to measure potency of extract concentrates, patient prescription dilute extracts, and mixes containing degrading enzymes will be discussed. Recent findings Information about the allergen extract active ingredient components contributing to potency is increasing. Pertinent stability issues include the type of diluent used for extraction and mixing. Fifty percent glycerin greatly extends the time over which extracts remain potent, including in mixes with fungal and insect extracts known to contain protein-degrading enzymes. Diluents that contain additional protein content such as human serum albumin increase stability of dilute solutions. Many of the most rigorous studies on allergen stability have been performed by allergenic extract manufacturers in support of Food and Drug Administration approved dating for standardized products and are not published. Summary Studies addressing how antigens in extracts change under various storage conditions have provided general guidance for expiration dating, but the diversity of extracts and testing methods have been less than complete. Additional findings that are increasing our knowledge of extract shelf life will be discussed.