What is the first-line treatment for an allergic hypersensitivity reaction?

• A. Epinephrine
• B. Oxygen
• C. Antihistamines
• D. Basic Life Support

Answer: (A)

In an allergic reaction that becomes anaphylaxis, the fastest way to reverse danger from airway swelling and shock is intramuscular epinephrine. Epinephrine acts on multiple receptors to counteract the reaction: alpha-adrenergic effects cause vasoconstriction that raises blood pressure and reduces facial and airway edema; beta-1 effects support heart function; and beta-2 effects relax bronchial smooth muscle to improve breathing and help curb mediator release from immune cells. This combination directly addresses the life-threatening features of anaphylaxis—airway obstruction, wheezing, swelling, and hypotension—making it the immediate, first-line treatment. Supplemental oxygen can help with oxygen levels but does not stop the underlying reaction; antihistamines may ease itching and hives but won’t prevent airway collapse or shock; Basic Life Support is reserved for situations where breathing or a pulse is absent. In practice, deliver the standard intramuscular dose promptly (adult typically 0.3 mg; pediatric dosing is weight-based, commonly 0.01 mg/kg up to 0.3 mg), reassess quickly, and seek emergency help for further management.