Epinephrine auto-injector needle length: what is the ideal length?
The purpose of this manuscript is to review the literature on the clinical effects of the needle length of epinephrine (adrenaline) auto-injectors.



Epinephrine has maximal pharmacodynamic effect within 10 min of intramuscular administration into the thigh. Prefilled epinephrine auto-injectors are designed for simplicity of use and safety. Auto-injectors are primarily used by patients in an unsupervised setting in cases of anaphylaxis. There are weight-appropriate doses of epinephrine available with auto-injectors that are prefilled, to prevent dosing errors, with 0.15, 0.30, and 0.50 mg amounts. In addition, needle lengths vary from 1.17 to 2.50 cm. The recommended needle lengths differ between adults and pediatric patients. In addition, the needle lengths differ between devices as well. There are concerns that the needle length may be too short in select obese patients. Yet, there are also concerns that the needle length may be too long in some patients. Factors that affect the depth of the injection, and therefore the pharmacokinetics of the drug, include not only the needle length but also the BMI, obesity, compression of soft tissue, and propulsion.



Epinephrine auto-injectors have different needle lengths. Using the right device with appropriate needle length based on BMI, obesity, and employing the proper technique can improve the outcome in an anaphylactic event.
aUniversity of Washington, Department of Medicine, Division of Allergy and Infectious Diseases, Seattle, Washington bDepartment of Medicine and Pediatrics, University of Tennessee College of Medicine, Memphis, Tennessee, USA.
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D000328:Adult; D000707:Anaphylaxis / Q000188:drug therapy*; D000818:Animals; D002648:Child; D004837:Epinephrine / Q000627:therapeutic use*; D006801:Humans; D007273:Injections, Intramuscular; D009339:Needles; D012646:Self Administration
D004837:Epinephrine