After administering an IV antibiotic, the client develops difficulty breathing, urticaria, and hypotension. What is the priority action?

This is anaphylactic reaction to the IV antibiotic. Anaphylaxis is a life-threatening systemic allergic reaction requiring immediate action: (1) Stop the offending agent immediately — close the IV clamp; (2) Maintain the airway — anaphylaxis can cause rapid laryngeal swelling; (3) Call for help (rapid response or code team); (4) Administer epinephrine IM (0.3-0.5 mg adult dose, 1:1000 solution, IM in vastus lateralis) — epinephrine is first-line and given immediately; (5) Position supine with legs elevated unless respiratory distress requires head elevated; (6) Apply high-flow oxygen; (7) Establish second IV; bolus fluids for hypotension; (8) Continuous monitoring; (9) Prepare for intubation. Secondary medications: diphenhydramine (antihistamine), methylprednisolone (corticosteroid), bronchodilator if wheezing. After stabilization: identify the allergen, document the reaction, update the medical record allergy list, place an allergy band, educate the client and family. Biphasic reactions can occur 8-12 hours later, so observation period is required.