Allergenic extracts that are considered non-standardized do not undergo additional laboratory testing to verify relative biologic strength. Instead, non-standardized extracts are assigned potency values based on either the product’s extraction ratio (source material-to-extracting solution) or on an estimated measure of total protein.
This is simply a ratio of grams of dry raw material (e.g. pollen) to volume of extraction solution. For example, 1:10 w/v means there is 1 gram of pollen per 10 mL of solution. Generally an extract will be more potent if it is extracted in a lower volume of solution (i.e. is less dilute). 1:10 w/v of a specific product can be assumed to be more potent than 1:20 w/v of the same product since it is twice as concentrated. The potency of an extract, however, also depends on the quality of the raw material, which naturally varies between lots and manufacturers.
Care should be taken when administering these products. ALK recommends a dose reduction of 50% when beginning any new vial of w/v extract to compensate for a potential jump in potency. Certain highly sensitive patients may require a greater dose adjustment depending on their tolerance.
Protein Nitrogen Units (PNU):
This is a measure of nitrogen found in solution. Since nitrogen is an integral part of all proteins its concentration can be used as a surrogate for protein concentration. There may be more consistency in these products since the extracts are measured quantitatively and are adjusted to match the lot’s intended PNU. However, it should be noted that PNU is a non-specific measure that may not necessarily capture the concentration of relevant allergenic proteins. Since lot-to-lot variability must be assumed, the same caution should be used when starting a new PNU vial as with a w/v vial.
Potency Labels for Non-Standard Extracts
|Extract Value||Units||Potency Determination||Example Concentrations|
|Weight-to-Volume||Units||Ratio of dry source material to volume of extraction||1:10w/v, 1:20w/v|
|Protein Nitrogen Units||PNU||Measure of nitrogen content||10,000PNU, 20,000PNU|