Epinephrine IM for Anaphylaxis

Epinephrine dosing and administration for anaphylaxis can be a tricky situation. In a strange, non-conformist type of stubbornness, the concentration parenteral epinephrine products are listed as a ratio (1:1000 vs 1:10,000 vs 1:100,000), rather than a percentage. There have been numerous reports, and personal experiences, where patients end up getting a significant overdose, or underdose of epi from miscommunication, dosing error or picking the wrong ampule/vial/syringe.

An often-overlooked administration (won’t call it an error) issue is administering epinephrine for anaphylaxis SubQ. When epi is administered SubQ, its alpha agonist properties (vasoconstriction) predominate, limiting blood flow to the area and therefore absorption into systemic circulation.

When administered IM, on the other hand, the beta-2 agonist properties (vasodilation) predominate in skeletal muscle, allowing for rapid absorption.  Importantly, the site of IM administration plays a large role: the preferred site for IM administration being the vastus lateralis.

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