HealthDay News — Administering epinephrine auto-injectors in the lower half of the thigh in overweight and obese children experiencing serious life-threatening anaphylaxis may help insure the therapy is effective, according to researchers at the American Academy of Allergy, Asthma & Immunology 2013 meeting.

Peter Arkwright, MD, PhD, from the University of Manchester in the United Kingdom, and colleagues used ultrasound to measure skin-surface-to-muscle depth at three defined distances down the thigh and leg in 93 children seen at pediatric allergy clinics. Body mass index (BMI) and waist circumference were also measured.

The researchers observed a significant association between higher weight (area under the receiver operating char a skin-surface-to-muscle depth greater than auto-injector needle lengthcteristic curve, 0.68), BMI (0.84) and waist circumference (0.72). Age and gender were not significantly associated with skin-surface-to-muscle depth greater than auto-injector needle length.

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At a distance of one-quarter down the thigh, 82% of obese children and 25% of non-obese children had skin-surface-to-muscle depth greater than needle length. Moving the injection site to three-quarters of the way down the thigh, improved this ratio — 17% of obese children and 2% of non-obese children had a skin-surface-to-muscle depth greater than the needle depth.

Moving the injection site even further down the leg, to the half way point on the calf insured that skin-surface-to-muscle depth was less then auto-injector needle in all children.

“Based on our study, injecting epinephrine into the lower rather than upper thigh would be advised in overweight or obese children,” Arkwright said in a press release. “If a child is experiencing anaphylaxis, this information would be important for a caregiver to know so that epinephrine can be administered into the child’s muscle in the most effective way.”


  1. Arkwright P et al. #713. Anatomical and anthropometric determinants of intramuscular versus subcutaneous administration in children with epinephrine auto-injectors. Presented at: American Academy of Allergy, Asthma and Immunology 2013 Meeting. Feb. 22-26, 2013. San Antonio.