Which class blocks parasympathetic nerve impulses and decreases oral and respiratory secretions?

• A. Antihistamine
• B. Anticholinergic
• C. Cholinergic agonist
• D. Adrenergic agent

Answer: (B)

Blocking parasympathetic nerve impulses reduces secretions because the parasympathetic system uses acetylcholine to stimulate salivary and bronchial glands via muscarinic receptors. Anticholinergic drugs are muscarinic receptor antagonists; by blocking acetylcholine at these receptors, they prevent gland stimulation, leading to decreased oral and respiratory secretions. This mechanism explains why these drugs are often used to produce a dry mouth and reduce airway secretions during procedures. Common examples include atropine and glycopyrrolate.

Antihistamines target histamine receptors and mainly address allergic symptoms; they don’t primarily block parasympathetic impulses. Cholinergic agonists, in contrast, mimic acetylcholine and increase parasympathetic activity, which would raise secretions rather than decrease them. Adrenergic agents stimulate the sympathetic system and can alter secretions indirectly, but they do not block parasympathetic signals in the same way as anticholinergics.