What is the first-line treatment for anaphylaxis and route?

• A. Epinephrine intramuscular injection; ensure airway, provide oxygen and IV fluids
• B. Intravenous epinephrine infusion
• C. Subcutaneous epinephrine injection
• D. Diphenhydramine alone without airway management

Answer: (A)

Anaphylaxis must be treated first and foremost with epinephrine given by intramuscular injection. This route is preferred because it delivers a rapid, reliable dose that quickly combats the major problems: airway edema and bronchospasm as well as the distributive shock from vasodilation. Epinephrine works on multiple receptors to make a difference: alpha-1 constricts blood vessels in the airway and skin to reduce swelling and support blood pressure, beta-1 increases heart output, and beta-2 relaxes bronchial smooth muscle to relieve bronchoconstriction and helps halt further mediator release.

Intramuscular administration into the thigh provides fast absorption and a safer, more controlled response in most settings. Intravenous epinephrine, while used in severe or monitored hospital cases, carries higher risks of dangerous heart rhythms and blood pressure swings and is not the first choice in an unmonitored environment. Subcutaneous injection is slower and can result in a delayed, weaker response in rapidly evolving reactions. Although antihistamines like diphenhydramine can help with itching and hives, they do not reverse throat swelling or low blood pressure and should never be used alone as the primary treatment.

Alongside epinephrine, ensure airway management, provide oxygen, and start IV fluids to support circulation. These measures address immediate needs while epinephrine targets the underlying pathophysiology to reverse the reaction quickly.