Biphasic Reactions After Anaphylaxis Are Rare

Biphasic reactions are defined as a recurrence of symptoms after a symptom-free period following anaphylaxis. In older studies, as many as 25% of patients experienced biphasic reactions, but more recent studies suggest a much lower rate.

In a retrospective chart review, 83 cases of anaphylaxis in adults and children admitted to an intensive care unit in Denmark were examined for biphasic reactions. The most common triggers were antibiotics, radiocontrast, and chemotherapy. One probable and three possible cases of biphasic reactions were identified, for an incidence of 4.8%. All cases were mild cutaneous reactions with mean onset of 14 hours.