(HealthDay News) – In obese and overweight children, epinephrine auto-injectors need to be administered in the lower half of the thigh, according to a study presented at the annual meeting of the American Academy of Allergy, Asthma & Immunology, held from Feb. 22–26 in San Antonio.

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 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 characteristic curve, 0.68), BMI (0.84), and waist circumference (0.72) and a skin-surface-to-muscle depth greater than auto-injector needle length. Age and gender were not significantly associated with skin-surface-to-muscle depth greater than auto-injector needle length. 82% of obese children and 25% of non-obese children had skin-surface-to-muscle depth greater than needle length at a distance of one-quarter down the thigh, while at a distance of three-quarters of the way down the thigh, skin-surface-to-muscle depth was greater than needle depth in 17% of obese children and 2% of non-obese children. Half way down the calf, all children’s skin-surface-to-muscle depth was less than auto-injector needle.

“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 statement. “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.”

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