**Core Concept**
The patient is experiencing anaphylaxis, a severe, life-threatening allergic reaction that requires immediate medical attention. Anaphylaxis is caused by the release of histamine and other mediators from mast cells, leading to increased vascular permeability, smooth muscle contraction, and bronchospasm.

**Why the Correct Answer is Right**
Epinephrine (adrenaline) is the first-line treatment for anaphylaxis. It works by binding to alpha-1 receptors on smooth muscle cells, causing vasoconstriction and reducing vascular permeability. Epinephrine also binds to beta-2 receptors on bronchial smooth muscle cells, causing bronchodilation and relieving bronchospasm. Additionally, epinephrine inhibits the release of histamine from mast cells, further reducing the severity of the allergic reaction.

**Why Each Wrong Option is Incorrect**
**Option A:** Antihistamines, such as diphenhydramine, can provide symptomatic relief for mild allergic reactions, but they are not sufficient to treat anaphylaxis.
**Option B:** Corticosteroids, such as prednisone, can help reduce inflammation and prevent further allergic reactions, but they do not provide immediate relief for anaphylaxis.
**Option C:** Bronchodilators, such as albuterol, can help relieve bronchospasm, but they do not address the underlying cause of anaphylaxis.

**Clinical Pearl / High-Yield Fact**
In cases of anaphylaxis, epinephrine should be administered via intramuscular injection (IM) in the mid-outer thigh, as this allows for rapid absorption and onset of action. It is essential to note that epinephrine is the primary treatment for anaphylaxis, and antihistamines and corticosteroids may be used as adjunctive therapies.

**Correct Answer:** C. Epinephrine (adrenaline) via intramuscular injection.