Which of the following is a first-generation H1 blocker?

Which of the following is a first-generation H1 blocker?

• A. Promethazine
• B. Cetirizine
• C. Loratadine
• D. Fexofenadine

Answer: (A)

First-generation H1 antagonists are known for their ability to cross the blood–brain barrier and cause central nervous system effects like sedation, along with anticholinergic side effects. Promethazine fits this profile: it is a classic H1 blocker with strong sedative and antiemetic properties because it readily enters the CNS and has anticholinergic actions. The other listed drugs are second-generation antihistamines designed to minimize CNS penetration, so they are much less sedating and have fewer anticholinergic effects. Thus, Promethazine is the first-generation H1 blocker.

First-generation H1 antagonists are known for their ability to cross the blood–brain barrier and cause central nervous system effects like sedation, along with anticholinergic side effects. Promethazine fits this profile: it is a classic H1 blocker with strong sedative and antiemetic properties because it readily enters the CNS and has anticholinergic actions. The other listed drugs are second-generation antihistamines designed to minimize CNS penetration, so they are much less sedating and have fewer anticholinergic effects. Thus, Promethazine is the first-generation H1 blocker.