First-line treatment for anaphylaxis.

• A. Intramuscular epinephrine 0.3–0.5 mg of 1:1000 solution
• B. Intravenous epinephrine infusion
• C. Diphenhydramine
• D. Albuterol inhalation

Answer: (A)

Epinephrine given intramuscularly is the first-line treatment for anaphylaxis because it rapidly counteracts the major life-threatening features by working on multiple receptor pathways. Alpha-1 effects cause vasoconstriction that reduces airway and facial swelling and helps raise blood pressure. Beta-1 effects increase heart rate and contractility, supporting perfusion during shock. Beta-2 effects promote bronchodilation and help stabilize the airway, while also dampening further mediator release from mast cells. The standard adult dose is 0.3–0.5 mg of a 1:1000 epinephrine solution, injected into the mid-outer thigh for quick absorption. If symptoms persist or recur, a second dose can be given after several minutes. IV epinephrine infusion is reserved for severe, refractory cases under close monitoring because it carries a higher risk of dangerous cardiovascular effects. Antihistamines and inhaled beta-agonists may help with symptoms but do not reverse the underlying pathophysiology of anaphylaxis and are not sufficient as the primary treatment.