Snapshot A 30-year-old woman prepares to fly over 12 hours on a business trip. She is expected to give a very important presentation upon arrival and is nervous about her history of motion sickness with long flights. She has tried dimenhydrinate and meclizine in the past without much help. Her physician suggests trying scopolamine patches but warns her of the most common side effect of dry mouth. Pirenzepine Drugs scopolamine aprepitant dimenhydrinate meclizine promethazine Anti-Emetics Scopolamine Aprepitant Anti-Histamines Mechanism of action Muscarinic antagonist in the central nervous system Substance P antagonist Blocks neurokinin-1 receptors in the central nervous system Dimenhydrinate First generation anti-histamine Meclizine Anti-histamine Also has mild anti-cholinergic effects Promethazine Anti-histamine Also has dopamine receptor angatonism Clinical use Motion sickness Anti-emetic, in the setting of chemotherapy Motion sickness Nausea and vomiting (promethazine) - Adverse effects Dry mouth Drowsiness Dizziness Blurry vision Induces CYP3A4 Headache Constipation Drowsiness Anti-cholinergic effects Acute glaucoma Dry mouth Extrapyramidal symptoms (promethazine) -