Which of the following is given to prevent hypersensitivity reactions?

• A. ondansetron
• B. lorazepam
• C. ibuprofen
• D. diphenhydramine

Answer: (D)

Preventing hypersensitivity reactions relies on blocking histamine effects. Hypersensitivity during therapy is often driven by histamine release from mast cells, causing symptoms like itching, hives, flushing, and sometimes bronchospasm. Diphenhydramine is an H1 antihistamine that blocks these receptors, reducing histamine’s effects and helping prevent the reaction when a triggering agent is given. The other drugs serve different roles: ondansetron prevents nausea and vomiting; lorazepam is used for anxiety or sedation; ibuprofen is an anti-inflammatory drug that isn’t used to prevent histamine-mediated reactions. So, diphenhydramine is the appropriate choice to prevent hypersensitivity reactions.