The patient's symptoms (urticaria, bronchospasm, hypotension) are classic signs of an anaphylactoid reaction (severe allergic-like reaction) to iodinated contrast. The most appropriate initial management for a severe anaphylactoid reaction is intramuscular epinephrine. Epinephrine acts as an alpha- and beta-adrenergic agonist, reversing bronchospasm, increasing blood pressure, and reducing mast cell degranulation. Diphenhydramine (antihistamine) and hydrocortisone (corticosteroid) are adjunctive therapies that can help with symptoms but are not first-line for life-threatening reactions. An intravenous normal saline bolus (Option D) can help with hypotension but does not address the underlying systemic reaction as effectively as epinephrine.
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