The Glycerin Associated Pain (GAP) Study

Fifty percent glycerin is often used in allergen immunotherapy (AIT) extracts to preserve extract potency.1 However, glycerin is also an irritant and it is recommended to dilute glycerin to reduce pain and inflammation associated with immunotherapy.2, 3 The 2011 allergen immunotherapy practice parameter warns that "higher glycerin concentrations are associated with injection pain, which correlates with the total amount of glycerin injected."4 To date, two studies evaluating the role of glycerin during allergen immunotherapy differed regarding their methods and conclusions.

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