Snapshot A 45-year-old woman with a history of metastatic sarcoma presents to the infusion center for chemotherapy infusion. She has experienced nausea and vomiting in the past with each infusion, which did not improve with ondansetron. Today, she is told that she can try another medication, aprepitant, which has worked for some patients who could not tolerate ondansetron. This could be given intravenously or by pill. She opts for the intravenous option as her nausea is often debilitating. 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 Promethazine: Anti-histamine Also has dopamine receptor angatonism Meclizine: Anti-histamine Also has mild anti-cholinergic effects Clinical Use Motion sickness Anti-emetic, in the setting of chemotherapy Motion sickness Nausea and vomiting (Promoethazone) Adverse effects Dry mouth Drowsiness Dizziness Blurry vision Induces CYP3A4 Headache Constipation Drowsiness Anti-cholinergic effects Acute Glaucoma Dry mouth Extrapyramidal symptoms (promethazine)