Epinephrine injection, preferably by the intramuscular (IM) route, is the standard of care initial treatment for anaphylaxis. EpiPen® (Dey, Napa, CA) is the only commercially marketed epinephrine auto-injector in the US. This study was designed to test whether EpiPen® auto-injector for adults, with a needle length of 1.43cm, is of sufficient length for IM administration in both males and females.

We measured the anterolateral thigh subcutaneous tissue depth (SCTD) of a representative group of adult males and females using computed tomography images. Body Mass Index (BMI) was also measured for stratification according to commonly accepted definitions: underweight (below 18.5), normal (18.5–24.9), overweight (25.0–29.9) and obese (30.0 and above).

Based on data from 42 total subjects (22 male, 20 female), the mean SCTD for males was 0.74cm (range 0.29–3.47) and for females was 1.74cm (range 0.24–3.13). One obese male subject (4.5%) had a SCTD greater than 1.43cm compared to 12 (60%) female subjects (2 normal, 4 overweight and 6 obese BMI). These 13 individuals would not receive an injection by the preferred intramuscular route with a needle length of 1.43cm.

The anterolateral thigh subcutaneous tissue depth differs between males and females and does not appear to be explained by BMI. SCTD differences between males and females may necessitate a need for gender-specific epinephrine auto-injectors with different needle lengths.