SCIT Probable Effective Doses

Allergen immunotherapy: A practice parameter third update (2010)


  • Nonstandardized pollen extracts - when analyzed, the nonstandardized pollen extracts demonstrate potency that is similar to that of grass and ragweed, although with a wider range. A target dose of 0.5 mL of a 1:100 or 1:200wt/vol of nonstandardized extract is reasonable.
    • 1:100= 1000 mg/100 mL (or 10 mg/mL)
      • 0.5 mL of 10 mg/mL = 5 mg of allergen source material per maintenance injection
    • 1:200= 1000 mg/200 mL (or 5 mg/mL)
      • 0.5 mL of 5 mg/mL = 2.5 mg of allergen source material per maintenance injection



Allergen Extract Units

Concentration units - amount of allergen source material (e.g. pollen or dander) in a certain volume; used to describe "unstardardized" allergen extracts. Note that two extracts of the same allergen, labeled as the same concentration (in PNU or w/v), may not be of the same potency if produced by different manufacturers.
  • Protein nitrogen units (PNU): PNU is a measure of total protein content. Does not distinguish between allergenic and non-allergenic proteins. 1 PNU is equivalent to 0.01 mcg of protein nitrogen.
  • Weight to volume ratio (w/v): w/v is the ratio of the weight (in grams) of the source material to the volume (in mL) of extraction fluid used to produce the extract
    • E.g. a 1:100 extract of oak pollen is produced by adding 1 gram of oak pollen to 100 mL of diluent.

Potency units - Based upon tests performed on the skin or serum of patients allergic to the antigen.
  • Bioequivalent allergy unit (BAU)
    • Units endorsed by FDA for standardized extracts in the US.
    • Determined by the ID50EAL method (Intradermal Dilution for 50 mm sum of Erythema diameters determines bioequivalent Allergy units) which involves preparing a series of threefold dilutions of an extract and administering 0.5 mL intradermally to 15-20 highly allergic individuals. The dilution that induces an area of erythema with the sum of the longest diameter and midpoint (orthogonal) diameter equaling 50 mm is the D50. The mean D50 for the group is then assigned a potency in BAUs.
  • Biological unit (BU)
    • In Europe, the potency unit is based on the dose of allergen extract resulting in a wheal comparable in size to the wheal produced by a given concentration of histamine, in a group of patients allergic to the substance in question. This unit was originally called histamine equivalent potency (HEP).
    • The BU is not used commercially, as each manufacturer uses company-specific units based on its own in-house reference preparations.