How does epinephrine function in anaphylaxis and what is the recommended initial route of administration?

• A. Epinephrine reverses airway edema, bronchoconstriction, and hypotension via alpha- and beta-adrenergic effects; administered intramuscularly (mid-anterolateral thigh) with dosing per guidelines; repeat if needed.
• B. Only bronchodilator with inhalation route.
• C. Oral tablet that slowly releases.
• D. IV infusion as first-line.

Answer: (A)

In anaphylaxis, the rapid dose of epinephrine works on both alpha- and beta-adrenergic receptors to counter the three life-threatening features: airway swelling, bronchospasm, and low blood pressure. Alpha-1 effects cause vasoconstriction that reduces mucosal edema and helps raise blood pressure, while beta-1 effects increase heart rate and contractility to support perfusion. Beta-2 effects relax airway smooth muscle to relieve bronchospasm and also help limit further mediator release from mast cells. This combination addresses the major symptoms all at once, which is why epinephrine is the first-line therapy.

The best initial route is intramuscular injection into the mid-anterolateral thigh. This site provides the fastest and most reliable absorption in an emergency, allowing quick reversal of symptoms. Typical dosing is 0.3 mg for adults and 0.15 mg for children, with repeat doses every 5–15 minutes if symptoms persist or recur, using an auto-injector or proper syringe.

Inhaled bronchodilators can help with bronchospasm, but they don’t reverse airway edema or hypotension. An oral tablet is too slow to be useful in an acute reaction. Intravenous epinephrine is not first-line in most settings due to higher risk of severe cardiovascular side effects and requires close monitoring; it’s reserved for specific hospital situations.