Adequacy of the epinephrine autoinjector needle length in delivering epinephrine to the intramuscular tissues.
BACKGROUND
Epinephrine injected by an autoinjector in the anterolateral aspect of the thigh is the standard of care in the emergency self-treatment of anaphylaxis. In the United States, the autoinjector EpiPen is widely used for the self-treatment of anaphylaxis.


OBJECTIVE
To investigate whether EpiPen autoinjector, with a needle length of 1.43 cm, is sufficient for intramuscular delivery of epinephrine in men and women.


METHODS
The distance from skin to muscle in the anterolateral aspect of the thigh was measured in 50 men and 50 women who had undergone computed tomography of the thighs for other medical reasons. For each individual, body mass index (BMI; a measure of weight in kilograms divided by the square of height in meters) was also calculated, and the individuals were classified as underweight (BMI, < 18.5), normal (BMI, 18.5-24.9), overweight (BMI, 25.0-29.9), and obese (BMI, > or = 30.0) using standard definition.


RESULTS
In the study participants the mean +/- SD distance from skin to muscle was 0.66 +/- 0.47 cm for men and 1.48 +/- 0.72 cm for women (P < .001). One man (obese at a BMI of 42.2) and 21 women (11 obese with a mean BMI of 35.2, 6 overweight with a mean BMI of 30.1, and 4 normal with a mean BMI of 24.5) had a greater distance from skin to muscle than the EpiPen needle length of 1.43 cm.


CONCLUSIONS
The distance from skin to muscle for the anterolateral aspect of the thigh is higher in women compared with men. This difference suggests that EpiPen may not deliver epinephrine to the intramuscular tissue in many women.
Song
Ted T
TT
Department of Allergy and Immunology, Walter Reed Army Medical Center, Washington, DC 20307-5001, USA.
Nelson
Michael R
MR
Chang
James H
JH
Engler
Renata J M
RJ
Chowdhury
Badrul A
BA
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000707:Anaphylaxis / Q000188:drug therapy; D004837:Epinephrine / Q000008:administration & dosage* / Q000627:therapeutic use; D005260:Female; D006801:Humans; D007273:Injections, Intramuscular / Q000295:instrumentation; D008297:Male; D008875:Middle Aged; D009339:Needles / Q000592:standards*; D012737:Sex Factors; D013594:Syringes / Q000592:standards*; D013848:Thigh / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed
D004837:Epinephrine