BACKGROUND:
Studies assessing the use of antihistamines and corticosteroids for the treatment of anaphylaxis have not supported a conclusive effect.

OBJECTIVE:
To assess prehospital management of anaphylaxis by measuring the effect of epinephrine use compared with antihistamines and corticosteroids on negative outcomes of anaphylaxis (intensive care unit/hospital ward admission, multiple doses of epinephrine in the emergency department [ED], and intravenous fluids given in the ED).

METHODS:
The Cross-Canada Anaphylaxis Registry is a cohort study that enrolls anaphylaxis cases presenting to EDs in 5 Canadian provinces over a 6-year period. Participants were recruited prospectively and retrospectively and were excluded if the case did not meet the definition of anaphylaxis.

RESULTS:
A total of 3498 cases of anaphylaxis, of which 80.3% were children, presented to 9 EDs across Canada. Prehospital treatment with epinephrine was administered in 31% of cases, whereas antihistamines and corticosteroids were used in 46% and 2% of cases, respectively. Admission to the intensive care unit/hospital ward was associated with prehospital treatment with corticosteroids (adjusted odds ratio, 2.84; 95% confidence interval [CI], 1.55, 6.97) while adjusting for severity, treatment with epinephrine and antihistamines, asthma, sex, and age. Prehospital treatment with epinephrine (adjusted odds ratio, 0.23; 95% CI, 0.14, 0.38) and antihistamines (adjusted odds ratio, 0.61; 95% CI, 0.44, 0.85) decreased the likelihood of receiving multiple doses of epinephrine in the ED, while adjusting for severity, treatment with corticosteroids, asthma, sex, and age.

CONCLUSIONS:
Prompt epinephrine treatment is crucial. Use of antihistamines in conjunction with epinephrine may reduce the risk of uncontrolled reactions (administration of 2 or more doses of epinephrine in the ED), although our findings do not support the use of corticosteroids.