Ending Insect-Sting Treatments Too Soon May Be Dangerous

BUFFALO, N.Y. -- Close encounters with certain summertime insects can be painful, sometimes fatal, for people allergic to their stings.

Venom immunotherapy, a treatment in which patients, over a number of years, receive small amounts of the stinging insect’s venom until they become immune to its effects, has been a boon to these sufferers.

Questions remain, however, about how long the treatment should be continued. Some allergists recommend a set time period of three to five years; others prescribe therapy until a skin test indicates the sting sensitivity is gone.

Since venom immunotherapy can be costly and quite time-consuming, requiring weekly visits to a specialist, patients sometimes grow weary of the commitment and decide to stop therapy, thinking they have acquired sufficient immunity already.

Robert E. Reisman, M.D., an allergist/immunologist with more than 20 years of research in the field of insect stings, says this is ill-advised and can be dangerous, particularly for people who had a severe reaction initially.

His most recent study shows that patients who experienced a severe initial reaction were at risk of having an equally severe reaction when re-stung, if venom immunotherapy is stopped before skin tests are negative.

"Although this risk may still be considered relatively low -- 15 percent in this study -- and could diminish with further therapy, it seems prudent to recommend continuing therapy as long as the venom skin test remains positive," Reisman said.

A professor of medicine at the University at Buffalo and former chair of the American Board of Allergy and Immunology, Reisman studied 113 patients who: a) had an allergic reaction to a sting; b) underwent venom immunotherapy; c) stopped therapy and d) were stung again.

He reported in the Journal of Allergy and Clinical Immunology that only 4 percent of patients with a mild initial allergic response had a reaction to a re-sting, compared to 15 percent of patients with a severe initial reaction.

The reactions were not influenced by the length of immunotherapy or the time between stopping therapy and the re-sting, the results showed.

Eighteen patients who had negative skin tests before stopping venom immunotherapy had no reactions when re-stung.

"Two to three years is sufficient for patients who had mild to moderate anaphylaxis," he concluded. "Longer duration is advisable for patients who had severe symptoms and continue to have positive venom skin test results."