**Core Concept**
Anaphylaxis is a severe, life-threatening allergic reaction that involves the release of histamine and other mediators from mast cells, leading to vasodilation, increased vascular permeability, and smooth muscle contraction. Angioedema is a related condition characterized by localized swelling of the skin and mucous membranes due to increased vascular permeability.

**Why the Correct Answer is Right**
Epinephrine (adrenaline) is the drug of choice for treating anaphylaxis and angioedema. It works by stimulating alpha-adrenergic receptors to cause vasoconstriction, which helps to reduce the increased vascular permeability and swelling associated with anaphylaxis. Additionally, epinephrine stimulates beta-2 adrenergic receptors to cause bronchodilation, which helps to alleviate respiratory distress. Epinephrine also has a direct effect on mast cells, causing them to return to their normal state and reducing the release of histamine and other mediators.

**Why Each Wrong Option is Incorrect**
**Option A:** Antihistamines, such as diphenhydramine, may be used to treat mild allergic reactions but are not effective in treating anaphylaxis or angioedema.
**Option B:** Corticosteroids, such as prednisone, may be used to prevent or treat allergic reactions but are not effective in treating acute anaphylaxis or angioedema.
**Option C:** Bronchodilators, such as albuterol, may be used to treat respiratory distress associated with anaphylaxis but are not effective in treating the underlying condition.

**Clinical Pearl / High-Yield Fact**
In anaphylaxis, epinephrine is the drug of choice because it works rapidly to alleviate symptoms and prevent progression of the reaction. It is essential to administer epinephrine via intramuscular injection as soon as possible in the event of an anaphylactic reaction.

**Correct Answer:** C. Epinephrine.