Children under 15 kg with food allergy may be at risk of having epinephrine auto-injectors administered into bone.

Background: The Epipen® Jr and Allerject® 0.15 mg are currently the most commonly prescribed epinephrine auto-injectors (EAIs) for the management of anaphylaxis in pediatric patients in North America and Canada. To ensure rapid absorption, it should be administered intramuscularly into the anterolateral aspect of the thigh. We examined whether the 12.7-mm needle length of the Epipen® Jr and Allerject® 0.15 mg is adequate for delivering epinephrine intramuscularly in pediatric patients who weighed <15 kg.

Methods: Consecutive pediatric patients with food allergy weighing <15 kg who required an EAI were included. Ultrasounds of the mid-anterolateral thigh were performed under minimal (min) and maximal (max) pressure. Skin-to-muscle depth (STMD) and skin-to-bone depth (STBD) measurements were completed. Baseline characteristics were compared between patients with a STBDmax <12.7 mm vs. ≥12.7 mm. Linear regression including variables such as age, sex, body mass index (BMI) and race was performed. The proportion of patients with a STBDmax <12.7 mm was compared in those weighing <10 kg vs. 10-14.9 kg.

Results: One hundred patients were included; 29 (29%) had STBDmax <12.7 mm. Height (p = 0.02) and weight (p = 0.0002) differed significantly between the two groups. Approximately 19% of those weighing 10-14.9 kg and 60% of those <10 kg had a STBDmax <12.7 mm. In the multivariable regression analysis, BMI was found to be a significant predictor of STBDmax.

Conclusions: A large proportion of children <15 kg prescribed an EAI is at risk of having the auto-injector administered into bone. Since alternative EAIs with shorter needle lengths are not currently available, EAIs should be prescribed with appropriate counselling in this population.