# Impact of Treatment on Rate of Biphasic Reaction in Children with Anaphylaxis

## TL;DR

This study found that most biphasic reactions in children with anaphylaxis occur within the first four hours after treatment with epinephrine and a corticosteroid.

## Contribution

The study provides new evidence that the risk of biphasic reactions significantly decreases after four hours of treatment with epinephrine and corticosteroids.

## Key findings

- Approximately 14% of children with anaphylaxis experienced a biphasic reaction within the first four hours of treatment.
- No biphasic reactions occurred after four hours, indicating a low risk of recurrence beyond this period.
- Most biphasic reactions required only one additional dose of epinephrine for resolution.

## Abstract

Our goal was to characterize a large group of children presenting to the emergency department (ED) with acute anaphylaxis, treated with intramuscular epinephrine (IM EPI) and a corticosteroid (CS), and to determine the impact of pharmacologic intervention on the rate and timing of biphasic reactions (BPR).

We reviewed consecutive children diagnosed with acute anaphylaxis managed in three EDs during a six-year period. All received IM EPI and CS, followed by monitoring for 4–6 hours post-treatment. We analyzed the rate and timing of BPR, comparing the intervals of 0–4 vs 4–48 hours after initiating therapy.

During the study period, there were 371 cases of anaphylaxis, of which 357 (94%) received both IM EPI and CS. Of these, 49 (14%) manifested BPR [84% had received prehospital IM EPI] requiring at least one additional dose of IM EPI [14% required ≥2 additional doses]. All BPR episodes occurred within the 0–4 hour interval after initiating therapy, whereas no patient manifested a BPR requiring an additional dose of IM EPI during the 4–48 hours after initiating therapy (P = <0.001, 95% CI 0–1.3%). No patient returned to the ED with recurrence of anaphylaxis symptoms within 48 hours after discharge.

Approximately 1 in 7 children with anaphylaxis experience a biphasic reaction after receiving intramuscular epinephrine. Children with anaphylaxis who exhibit symptomatic resolution four hours following initiation of therapy have a low risk for subsequently developing BPR. Most BPR cases required only one additional dose of IM EPI to effect resolution. The rate of BPR in those receiving IM EPI and a corticosteroid is significantly lower >4 hours vs <4 hours after initiating therapy.