Within 5 minutes after a bee sting, a 15-year-old girl suddenly has difficulty breathing, with marked inspiratory stridor from laryngeal edema. She experiences marked urticaria and notes swelling of the hand that was stung. Which of the following is the best pharmacologic agent to treat her signs and symptoms?

**Core Concept**
The patient is experiencing anaphylaxis, a severe, life-threatening allergic reaction characterized by airway edema, urticaria, and cardiovascular collapse. The goal of treatment is to rapidly alleviate airway obstruction and restore circulation.

**Why the Correct Answer is Right**
Epinephrine (adrenaline) is the first-line treatment for anaphylaxis due to its ability to rapidly relax smooth muscle, improve airway patency, and increase vascular tone. It acts by stimulating beta-2 adrenergic receptors, causing bronchodilation, and alpha-1 adrenergic receptors, causing vasoconstriction. This helps to alleviate inspiratory stridor, urticaria, and swelling associated with anaphylaxis.

**Why Each Wrong Option is Incorrect**
**Option A:** Antihistamines, such as diphenhydramine, may provide some relief from urticaria and itching but are not sufficient to treat anaphylaxis due to their delayed onset of action and limited ability to alleviate airway obstruction.

**Option B:** Corticosteroids, such as prednisone, may help to reduce inflammation and prevent late-phase reactions but are not effective in rapidly alleviating the acute symptoms of anaphylaxis.

**Option C:** Bronchodilators, such as albuterol, may help to alleviate bronchospasm but do not address the underlying cause of anaphylaxis and may not be sufficient to treat laryngeal edema.

**Option D:** Vasopressors, such as norepinephrine, may be used to treat hypotension associated with anaphylaxis but are not the first-line treatment for anaphylaxis due to their potential to worsen airway obstruction.

**Clinical Pearl / High-Yield Fact**
Mnemonics such as "Epinephrine is the first line" or "AEIOU" (Allergy, Enlarged face, Intense anxiety, Onset after sting, Urticaria) can help students remember the key features of anaphylaxis and the importance of prompt epinephrine administration.

**Correct Answer:** C. Epinephrine (adrenaline).

✓ Correct Answer: B. Epinephrine