Which drug is an antihistamine?

• A. Miconzol 1%
• B. Galliprant
• C. Carprofen
• D. Diphenhydramine

Answer: (D)

Antihistamines work by blocking histamine at H1 receptors, which helps prevent the typical allergy symptoms such as itching, swelling, and sneezing. Diphenhydramine is a classic H1 blocker used in veterinary medicine to treat allergic reactions, pruritus, and urticaria, and it can also serve as an antiemetic in some cases because of its central effects. It often causes drowsiness since it crosses the blood–brain barrier, and some animals may experience dry mouth or urinary retention as side effects. The other drugs listed do not act as antihistamines: one is a topical antifungal, another is a prostaglandin E2 receptor antagonist used for osteoarthritis pain, and the last is a nonsteroidal anti-inflammatory drug for pain and inflammation. Therefore, diphenhydramine is the antihistamine among these options.