Biphasic reactions can occur 2 to 72 hours after resolution of the initial anaphylactic episode. Therefore, many experts advocate for 8 to 24 hours’ observation after an anaphylactic reaction, a recommendation with significant social and economic impact on patients, families, and our healthcare system. Previous investigations in adults had reported that between 5% and 20% of anaphylactic episodes were complicated by a biphasic reaction, but this topic had not been studied in pediatrics.

Retrospective, unblinded chart review of all children admitted to a large US urban children’s hospital from 1985 to 1999.