Long-term efficacy of venom immunotherapy.

Background: The long-term efficacy of venom immunotherapy (VIT) in patients who either prematurely discontinue VIT or who experience subsequent stings after discontinuation of VIT remains uncertain. Objective: To survey sting reaction patterns in patients who had previously discontinued VIT. Methods: Patients who had received VIT between January 1, 1984, and December 31, 2004 were sent a questionnaire inquiring whether they had been stung by an insect to which the VIT had been directed. Symptoms that developed were assessed. The patients were subsequently contacted by telephone to clarify their responses. Results: Of 227 patients who responded to the questionnaire, 181 (79.7%) received VIT for more than 3 years; 100 of these 181 patients (55.2%) were stung after discontinuing VIT. At the time of the first sting after stopping VIT, 92 patients had a local reaction and 8 had a systemic reaction. Of 40 patients who were Stung more than once after ending VIT, 7 (17.5%) experienced reactions of greater severity with the subsequent stings. All the patients reported that their reactions after ending VIT were milder than before treatment. The likelihood of systemic reactions to stings was almost identical in patients treated for either longer or shorter than 3 years with VIT. Conclusions: In most patients, VIT provides long-term protection from severe systemic reactions. Risk of systemic reactions increases with subsequent stings after ending VIT. All the patients reported that symptoms experienced with stings after stopping VIT were milder than symptoms before VIT.