Late systemic-allergic reactions to inhalant allergen immunotherapy.

Late systemic-allergic reactions (defined as occurring between 30 minutes and 6 hours after injection) to inhalant allergen immunotherapy were prospectively studied in four allergy treatment centers; 35,674 injections were administered to 712 patients. Twenty-nine patients (4% of all patients) experienced 33 late reactions. Fifty-six injections (0.16% of all injections) were associated with the 33 late reactions. The most common clinical manifestation of a late reaction was urticaria. However, objective respiratory airway involvement, as manifested by wheezing and/or stridor, occurred in 10 (27%) of the late reactions. Delayed reactions involving wheezing and/or stridor were only related to injections from maintenance vials, and all these more severe reactions occurred no later than 60 minutes after injection. We conclude that late systemic-allergic reactions account for a significant percent of the total number of systemic-allergic reactions to inhalant allergen immunotherapy. It is our belief that a 60-minute postinjection waiting period for injections administered from maintenance vials of extract would enhance the safety of inhalant allergen immunotherapy.