Venom immunotherapy reduces large local reactions to insect stings

Background: Large local reactions to insect stings cause significant morbidity and impair quality of life. Venom immunotherapy is not recommended because of a low risk for future systemic reaction and unproven efficacy in preventing large local reactions. Objective: To determine the feasibility of performing a controlled trial to examine the efficacy of venom immunotherapy in reducing the size and duration of large local reactions. Methods: Sting challenge in 41 patients with previous large local reactions and positive venom skin tests caused large local reactions 16 cm or larger in 34 patients, and 29 consented to treatment. Venom immunotherapy was initiated in 19, and 10 were untreated controls. Sting challenge was repeated after 7 to 11 weeks (control patients then began venom immunotherapy), and annually for as long as 4 years. Results: After 7 to 11 weeks of treatment, the size and duration of large local reactions decreased 42% and 53%, respectively, in treated patients and 18% in controls (P < .01 for both). The response was similar after 1 year, and improved after 2 to 4 years to 60% and 70%, respectively. Conclusions: Venom immunotherapy significantly reduced the size and duration of the large local reactions, and the efficacy improved over a period of 2 to 4 years of treatment. Further studies are needed to establish the safety and efficacy of venom immunotherapy for large local reactions, the optimal duration of treatment, and the mechanism for the differences in degree and rate of clinical response compared with venom immunotherapy in systemic reactors.