Incidence and characteristics of biphasic reactions after allergen immunotherapy

The reported incidence of biphasic anaphylactic reactions varies from 1% to 20%. Reported risk factors for biphasic reactions include a delay in epinephrine administration and a longer interval to initial improvement. To date, only 4 cases of biphasic reactions after allergen immunotherapy have been reported.

We sought to determine the incidence, clinical characteristics, and risk factors for biphasic reactions after allergen-specific immunotherapy.

Patients who were treated with epinephrine for systemic reactions after allergen immunotherapy were prospectively enrolled. Patients were assessed initially and at 24 hours by using a 31-symptom scoring system.

Sixty systemic reactions occurred in 55 patients; 14 (23%) biphasic reactions were reported. Patients experiencing biphasic reactions were more likely to be female (P = .03) and older (P = .01) and require greater than 1 dose of epinephrine (P = .001). There was no difference between groups (biphasic vs no biphasic reaction) regarding the type of immunotherapy, current asthma, initial symptom scores, or time to symptoms, initial epinephrine, or improvement. No specific symptom predicted biphasic reactions. Biphasic reactions were significantly less severe compared with the initial reaction (P < .001), did not occur in children, and did not require additional epinephrine.

Twenty-three percent of patients requiring epinephrine for systemic reactions caused by allergen immunotherapy experienced biphasic symptoms. Patients treated promptly with epinephrine for systemic reactions should be cautioned regarding biphasic reactions; however, biphasic reactions after allergen immunotherapy were mild and did not require additional epinephrine.