The GILL study: Glycerin-induced local reactions in immunotherapy

Background: The mechanism of local reactions is not well defined. Glycerin, an excellent preservative used commonly in immunotherapy extracts, is a recognized irritant. Objective: This study was undertaken to examine whether higher glycerin concentration in immunotherapy extracts is associated with an increase in local reaction rates during immunotherapy. Methods: A retrospective analysis of electronic immunotherapy records over a 12-month period was performed from a single site. A small local reaction was defined as induration and/or erythema at the injection site smaller than or equal to the size of the patient's palm. A large local reaction was defined as a reaction larger than the patient's palm. Results: Over the 12-month period, 360 patients received a total of 9678 immunotherapy injections. For all injections, the total local reaction rate was 16.3% (1574/9678), the small local reaction rate was 15.9% (1536/9678), and the large local reaction rate was 0.4% (38/9678). For aeroallergens, small local reaction rates increased significantly with increasing allergen concentrations, from 7.3% (1:1000 vol/vol) to 23.0% (1:1 vol/ vol; P < .001). The small local reaction rate was higher with increasing allergen content but not higher glycerin concentration. Large local reactions were infrequent and did not significantly increase with allergen or glycerin concentration. Conclusions: Small local, but not large local, reaction rates increase with higher allergen concentration, number, and volume. Higher glycerin concentrations (even 50%) are not associated with significantly higher small or large local reaction rates.