Which antihistamines are listed as H-1 receptor agonists used in this context?

• A. Phenergan and Vistaril
• B. Promethazine and Hydroxyzine
• C. Diphenhydramine and Cetirizine
• D. Loratadine and Fexofenadine

Answer: (A)

These drugs are H1 receptor antagonists, meaning they block histamine at the H1 site to provide antiemetic, sedative, and pruritus-relief effects often needed in inpatient antepartum care. Phenergan (promethazine) and Vistaril (hydroxyzine) are classic first‑generation antihistamines known for crossing into the central nervous system and delivering these effects. They’re commonly listed for this context because of their sedative and antiemetic properties. By contrast, second‑generation antihistamines like cetirizine, loratadine, and fexofenadine have less CNS penetration and are typically not used for antiemetic or sedation indications in this setting. Diphenhydramine is also a first‑generation option, but the pairing presented corresponds to promethazine and hydroxyzine, which is why this choice is the best fit.