**Core Concept**
This scenario describes an acute anaphylactic reaction to penicillin, a severe Type I hypersensitivity reaction involving rapid mast cell degranulation, leading to release of histamine and other mediators. The hallmark features—urticaria, angioedema, hypotension, and bronchospasm—point to systemic anaphylaxis requiring immediate intervention.

**Why the Correct Answer is Right**
Epinephrine is the first-line treatment for anaphylaxis due to its potent, multi-system effects: it constricts blood vessels to counteract hypotension, relaxes bronchial smooth muscle to relieve bronchospasm, and reduces capillary permeability to minimize edema. It acts on α1, α2, β1, and β2 receptors, providing rapid reversal of life-threatening symptoms. Administration must be intramuscular (not intravenous) and immediate, as it is the only treatment proven to reverse mortality in anaphylaxis.

**Why Each Wrong Option is Incorrect**
Option A: Chlorpheniramine is an H1-antihistamine with limited efficacy in acute anaphylaxis. It does not improve hypotension or bronchospasm and is ineffective in reversing life-threatening symptoms.
Option C: High-dose hydrocortisone is used in the management of anaphylaxis but only as adjunctive therapy, not first-line. It has delayed onset and no effect on acute vasodilation or bronchospasm.
Option D: Nebulized salbutamol is useful for bronchospasm but lacks the ability to treat hypotension or vascular instability. It is ineffective in anaphylaxis without epinephrine.

**Clinical Pearl / High-Yield Fact**
In anaphylaxis, **epinephrine is the only treatment that improves survival**—delaying or missing its administration increases mortality. Always administer IM epinephrine first, then consider adjuncts like antihistamines and corticosteroids.

✓ Correct Answer: B. Epinephrine inj.