Retrospective comparison between 0.3 mg and 0.5 mg dosing of intramuscular epinephrine for anaphylaxis

Anaphylaxis is an acute and life-threatening reaction. Intramuscular (IM) epinephrine is the first line agent for management. The World Allergy Organization recommends IM epinephrine 0.01 mg/kg, with a maximum dose of 0.5 mg. However, 0.3 mg is commonly used which may increase the risk of poor outcomes in adults greater than 50 kg. This study aims to investigate the incidence of escalating care after initial epinephrine dosing in management of anaphylaxis.

This retrospective study included patients who received IM epinephrine 0.3 or 0.5 mg for anaphylaxis within a single health system. The primary outcome was the incidence of escalating care after an initial dose of IM epinephrine, defined as an additional dose of IM epinephrine, epinephrine infusion initiation, or intubation. Secondary outcomes, including adverse effects, were compared between groups.

Of 338 meeting inclusion criteria, 254 and 84 patients were in the 0.3 mg and 0.5 mg groups, respectively. The primary composite outcome was significantly higher in the 0.3 mg group compared to the 0.5 mg group (29.5 % vs. 7.1 %, p < 0.001). Individual outcomes of an additional IM dose and infusion initiation were significantly higher in the 0.3 mg group. A multivariate logistic regression confirmed an initial dose of 0.5 mg epinephrine was independently associated with a lower incidence of the primary outcome.

Significantly fewer patients receiving an initial 0.5 mg IM epinephrine dose required escalation of care compared to those who received 0.3 mg. Future prospective studies are needed to confirm the results of this study.