Formulation Concern - Phenol
Many extracts contain phenol (0.4%) as a preservative. There have been some reports that phenol can impact the stability of allergenic extracts. However, more recent data has shown that phenol does not appear to have a significant impact on the long term potency of bulk concentrates stored under appropriate conditions. This is especially true of glycerinated extracts.
Use of phenol in allergenic extracts has been standard practice for many years. Currently the FDA requires that all aqueous extracts or diluents contain 0.4% phenol in order to maintain sterility. Because of this all diluted patient vials will ultimately be exposed to phenol, even if the bulk vials are phenol free. However, even under these conditions, it is unlikely that phenol will have a negative impact on extract stability since diluted vials are consumed quickly during a typical build up schedule.
For more information on why phenol is an essential component of allergen extracts, see the section on Aseptic Procedures & Sterility.