An 18-year-old woman develops uicaria and wheezing after an injection of intravenous contrast for an abdominal CT scan. Her blood pressure is 120/60 mm Hg, hea rate is 155 beats per minute, and respiratory rate is 30 breaths per minute. Which of the following is the most appropriate immediate therapy?

**Core Concept**
The patient is experiencing an allergic reaction to the intravenous contrast, likely anaphylaxis, characterized by a combination of urticaria, wheezing, tachycardia, tachypnea, and hypotension.

**Why the Correct Answer is Right**
The most effective treatment for anaphylaxis involves administering epinephrine (adrenaline) to rapidly reverse the symptoms. Epinephrine works by:

* Relaxing smooth muscle, thereby alleviating wheezing and bronchospasm
* Constricting blood vessels, which increases blood pressure
* Stabilizing mast cells and reducing the release of histamine, a key mediator of allergic reactions

Epinephrine is administered via intramuscular injection, typically in the mid-outer thigh.

**Why Each Wrong Option is Incorrect**

**Option A:** Antihistamines, such as diphenhydramine, may be used to alleviate symptoms of mild to moderate allergic reactions but are not effective in treating anaphylaxis.
**Option B:** Corticosteroids, such as hydrocortisone, are used to prevent or reduce the severity of allergic reactions but do not provide immediate relief in anaphylaxis.
**Option C:** Bronchodilators, such as albuterol, may be used to alleviate wheezing but do not address the underlying cause of anaphylaxis.

**Clinical Pearl / High-Yield Fact**
In anaphylaxis, epinephrine is the first-line treatment, and patients should carry an EpiPen or similar device for emergency situations. Antihistamines and corticosteroids may be used in conjunction with epinephrine, but epinephrine should always be administered first.

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

✓ Correct Answer: B. Epinephrine