From the Guidelines
The fastest route of epinephrine administration for anaphylaxis is intramuscular (IM) injection into the anterolateral thigh (vastus lateralis muscle). The recommended dose is 0.01 mg/kg of 1:1000 (1 mg/mL) epinephrine solution, with a maximum of 0.5 mg for adults and 0.3 mg for children, as stated in the most recent guideline update 1. This dose can be repeated every 5-15 minutes if symptoms persist.
Key Considerations
- The thigh muscle has excellent blood supply, allowing for quick absorption into circulation 1.
- In the setting of hypotension during anaphylaxis, peripheral vasoconstriction may make IV access difficult to obtain and delay treatment.
- Epinephrine works by constricting blood vessels, increasing blood pressure, relaxing bronchial smooth muscles to improve breathing, and reducing inflammation by preventing the release of mediators from mast cells and basophils 1.
Administration Details
- The IM dose should be given in the anterolateral thigh in the vastus lateralis muscle, as recommended by the guidelines 1.
- The availability of newer auto-injector dose formulations allows greater epinephrine dosing accuracy, but a 0.15-mg auto-injector dose is also widely prescribed for infants at risk for anaphylaxis 1.
- Depending on response to the initial injection, additional doses or alternative administration methods may be considered, such as adding epinephrine to a saline infusion 1.
Evidence Support
The most recent and highest quality study, published in 2020, supports the use of IM epinephrine injection in the thigh as the first-line treatment for anaphylaxis 1. This recommendation is based on the understanding of the pathophysiology of anaphylaxis and the mechanisms of action of epinephrine, as well as the available evidence on the effectiveness and safety of different administration routes and doses.
From the FDA Drug Label
DOSAGE AND ADMINISTRATION Anaphylaxis: Adults and Children 30 kg (66 lbs) or more: 0.3 to 0.5 mg (0.3 to 0.5 mL) intramuscularly or subcutaneously into anterolateral aspect of the thigh every 5 to 10 minutes as necessary Children 30 kg (66 lbs) or less: 0.01 mg/kg (0.01 mL/kg), up to 0.3 mg (0.3 mL), intramuscularly or subcutaneously into anterolateral aspect of the thigh every 5 to 10 minutes as necessary
The fastest route of epinephrine for anaphylaxis is intramuscularly into the anterolateral aspect of the thigh, as it is specified in the dosage administration section of the label 2.
- Key points:
- Intramuscular injection is the preferred route.
- Injection site is the anterolateral aspect of the thigh.
- Subcutaneous injection is also acceptable, but intramuscular is specified as an option, implying it may be faster.
From the Research
Fastest Route of Epinephrine Administration for Anaphylaxis
- The fastest and most effective route of epinephrine administration for anaphylaxis is intramuscularly, specifically in the anterolateral aspect of the mid-thigh 3, 4, 5, 6, 7.
- This route is preferred due to its rapid onset of action and superior therapeutic window compared to other routes such as subcutaneous or intravenous administration 3, 5.
- The use of epinephrine autoinjectors is also recommended for outpatient treatment, as they can control anaphylaxis quickly and effectively 6.
- In cases where patients are unresponsive to repeated intramuscular injections, a continuous infusion of epinephrine may be necessary 4.
- Intravenous epinephrine may be used in patients in shock, either as a bolus or infusion, along with fluid resuscitation 7.
Key Considerations
- Prompt administration of epinephrine is critical for survival in anaphylaxis, and any delays can result in increased morbidity and mortality 3, 4.
- Antihistamines and corticosteroids are second-line medications and should not be given in lieu of, or prior to, epinephrine 4.
- Aggressive fluid resuscitation should also be used to treat the intravascular volume depletion characteristic of anaphylaxis 4.