Antiemetics and Laxatives Quiz

See Antimuscarinics. Option E is correct because hyoscine hydrobromide is an antimuscarinic drug that crosses the blood-brain barrier, the tightly sealed lining of the brain's blood vessels, and blocks muscarinic receptors in the vestibular nuclei and the chemoreceptor trigger zone. Motion sickness arises when the vestibular system, the balance organs of the inner ear and the brainstem nuclei that receive their signals, is overstimulated and sends excessive signals to the vomiting centre in the medulla. The dominant receptors on this pathway are muscarinic (M) and histamine H1 receptors, so blocking muscarinic receptors reduces cholinergic (acetylcholine) transmission from the vestibular apparatus and prevents nausea and vomiting. Hyoscine hydrobromide is the standard treatment for motion sickness and is available as tablets or as a transdermal patch, which gives steady release for a long voyage. Its side effects are the typical antimuscarinic ones: dry mouth, blurred vision, urinary retention, constipation, drowsiness and confusion in older people, and it should be avoided in glaucoma and prostatic hyperplasia. A memory aid: hyoscine hydrobromide goes to the brain for travel sickness, whereas hyoscine butylbromide stays in the gut for cramps.

• Drug class: hyoscine hydrobromide is an antimuscarinic that crosses the blood-brain barrier.
• Site of action: it blocks muscarinic receptors in the vestibular nuclei and the chemoreceptor trigger zone.
• Use: standard treatment for motion sickness, as tablets or a transdermal patch.
• Cautions: dry mouth, blurred vision and urinary retention are typical, and avoid it in glaucoma and prostatic hyperplasia.