In-hospital sting challenge in insect venom-allergic patients after stopping venom immunotherapy.

Immunotherapy (IT) in venom-allergic patients has been demonstrated to provide a highly efficient protection from severe reactions to a re-sting. It is not known whether this protection will persist after IT is stopped in patients with remaining venom sensitivity. In 25 adult patients with a previous severe systemic reaction to a Hymenoptera insect sting, 28 in-hospital sting challenges after stopping IT resulted in no systemic reactions. The mean duration of venom IT was 42.8 months (range, 36 to 83 months), and the mean time interval from the time IT was stopped until sting challenge was, in mean, 25.2 months (range, 12 to 36 months). The mean venom-specific IgE after stopping IT was 2.4 PRU/ml (range, 0 to 16.9 PRU/ml), at the day of sting challenge, 2.7 PRU/ml (range, 0 to 22 PRU/ml), and 2 weeks later, 2.4 PRU/ml (range, 0.02 to 27.8 PRU/ml). These changes in IgE were not significant. Venom-specific IgG concentration when IT was stopped was 64 PU/ml (range, 20 to 144 PU/ml), decreasing significantly to the day of sting challenge to 41.1 PU/ml (range, 13 to 84 PU/ml), and 2 weeks later, a significant increase to a mean of 53.5 PU/ml (range, 12 to 117 PU/ml) was found. Our results suggest that venom IT may be stopped after 3 years, regardless of the level of specific antibodies. To confirm this finding, a larger number of patients should be studied.