Biphasic Reactions Are Rare Among Patients with Allergic Reactions

Patients with allergic reactions are often observed in the emergency department (ED) or hospital for 6 to 24 hours, even after stabilization. Investigators reviewed charts for visits for allergy or anaphylaxis at two Canadian EDs, to determine the incidence of clinically important biphasic reactions.

During the 5-year study period, there were 496 visits for anaphylaxis and 2323 for nonanaphylactic allergic reactions; in 54% and 21% of these visits, respectively, patients received epinephrine. Five clinically important biphasic reactions were identified: Two occurred in the anaphylaxis group (0.4%) during the ED visit, and three occurred in the allergic-reaction group (0.1%) between 1 and 6 days after discharge. There were no fatalities withi…