title: Auto-injector needle length may be inadequate to deliver epinephrine intramuscularly in women with confirmed food allergy.
abstract: BACKGROUND
  Epinephrine auto-injectors are the standard first aid treatment for anaphylaxis. Intramuscular delivery into the anterolateral aspect of the thigh is recommended for optimal onset of action of epinephrine. The most frequently prescribed auto-injector in North America and Canada is the EpiPen(®), which has a needle length of 15.2 mm. Currently, it is unknown whether this needle length is adequate for intramuscular delivery of epinephrine in adult patients at risk of anaphylaxis.
  
  
  METHODS
  One hundred consecutive adult patients with confirmed food allergy requiring an epinephrine auto-injector were recruited. Skin to muscle depth (STMD) at the right mid-anterolateral thigh was measured using ultrasound under minimal (min) and maximum (max) pressure. The EpiPen(®) needle length was considered adequate if STMDmax was ≤15.2 mm. Baseline characteristics including age, gender, ethnicity, and body mass index (BMI) were compared in patients with STMDmax ≤15.2 mm vs. >15.2 mm.
  
  
  RESULTS
  The EpiPen(®) needle length of 15.2 mm was inadequate for intramuscular delivery in 19 of the 100 enrolled patients (19%), all of whom were female; 28% of women had a STMDmax >15.2 mm. The mean STMDmax in the ≤15.2-mm and >15.2-mm groups were 9 ± 4 mm and 20 ± 4 mm, respectively (p = 0.0001). Linear regression analysis found BMI to be significantly associated with STMDmax after adjusting for age (p < 0.001).
  
  
  CONCLUSIONS
  The needle length of the epinephrine auto-injectors may not be adequate for intramuscular delivery of epinephrine in a large proportion of women with food allergy; this may impact morbidity and mortality from anaphylaxis in this patient population.
authors: Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada.
authors: Gina
authors: G
authors: Tsai
authors: Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada.
authors: Laura
authors: L
authors: Kim
authors: Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada ; Michael D. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada.
authors: Immaculate Fp
authors: IF
authors: Nevis
authors: Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada.
authors: Arunmozhi
authors: A
authors: Dominic
authors: Department of Biology, University of Waterloo, Waterloo, Ontario, Canada.
authors: Ryan
authors: R
authors: Potts
authors: Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada.
authors: Jack
authors: J
authors: Chiu
authors: Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada ; Michael D. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada ; 525 Belmont Avenue West, Suite 205, Kitchener, Ontario N2M 5E2, Canada.
authors: Harold L
authors: HL
authors: Kim
keywords: Anaphylaxis; Auto-injector; Epinephrine; Food allergy; Needle length; Skin-to-muscle depth