Which of the following statements about antihistamines is true?

• A. They stimulate histamine release
• B. They block histamine from binding to its receptors
• C. They are classified as cestodes
• D. They are effective against bacterial infections

Answer: (B)

Antihistamines work by blocking histamine from binding to its receptors. Histamine is a chemical released during allergic reactions and plays a key role in the immune response. When antihistamines are administered, they compete with histamine for binding to its receptors, effectively preventing the typical symptoms associated with allergies and histamine release, such as itching, swelling, and mucus production. This mechanism of action is critical for their effectiveness in treating allergic conditions such as hay fever, urticaria, and allergic conjunctivitis.

The other statements do not accurately describe antihistamines. They do not stimulate histamine release, nor are they classified as cestodes, which are a type of parasitic worm. Additionally, antihistamines are not effective against bacterial infections, as they do not possess antimicrobial properties. Thus, the statement about blocking histamine binding accurately reflects the pharmacological function of antihistamines.