A nurse is caring for a client who has urticaria following administration of an antibiotic. Which of the following medications should the nurse prepare to administer?

A. Diphenhydramine. Urticaria (hives) is a common allergic reaction often caused by medications like antibiotics. Diphenhydramine, an antihistamine, is used to treat allergic reactions by blocking histamine receptors, reducing itching, swelling, and rash. B. Hydralazine. This is an antihypertensive medication used to treat high blood pressure, not allergic reactions. It has no effect on histamine or allergic symptoms. C. Naloxone. Naloxone is an opioid antagonist used to reverse opioid overdose. It does not treat allergic reactions like urticaria unless the cause is opioid-induced (which is not indicated here). D. Protamine. Protamine is used to reverse the effects of heparin. It has no role in treating allergic reactions to antibiotics.