Nausea and Antiemetic Medications

Nausea and vomiting happens when the Vomiting Center in the medulla is stimulated by one of three different neurotransmitter pathways:

• Visceral Stimulation (of intestines, stomach) – i.e. nausea from gastroenteritis
  • mediated by dopamine and serotonin
• Chemoreceptor Trigger Zone (in medulla oblongata) – i.e. nausea from chemotherapy
  • mediated by dopamine and serotonin
• Vestibular Stimulation (in inner ear) – i.e. nausea from motion sickness
  • mediated by histamine and acetylcholine

Which antiemetic medication you choose depends on the type of nausea they have. For example, nausea from motion sickness should be treated with an antihistamine or anticholinergic medication, whereas nausea from gastroenteritis should be treated with a dopamine or serotonin antagonist. Once you choose the category of drugs to use, consider price and side effect profile when selecting the specific drug.

• Antihistamine
  •  Diphenhydramine (Benadryl), Meclizine (Antivert) – both are cheap, but sedating and dry you out (constipation, dry mouth, urinary retention)
• Anticholinergic
  • Scopolamine – not as sedating, so great for travelers who want to stay awake, but is expensive. The patch takes 6-8 hrs to work and lasts 72 hrs.
• Dopamine Antagonist
  • Metoclopramide (Reglan) – cheap, but has extrapyramidal side effects, so dont use in elderly or pts on antipsychotics
  • Prochlorperazine, Promethazine (Phenergan) – no extrapyramidal side effects, but not as cheap
• Serotonin Antagonist
  • Ondansetron – effective, but expensive and has risk of QT prolongation, so limit in pts with arrhythmias or when taking other meds that prolong QT.
• Natural/Alternative therapies
  • Pyridoxine (Vitamin B6) with or without Doxylamine – first-line treatment for nausea and vomiting of pregnancy. Limited evidence of it being effective for other types of nausea.
  • Ginger – thought to antagonize serotonin and cholinergic receptors, so theoretically works for most types of nausea.

Some other tid-bits:

• Nausea from migraines is mediated by dopamine, so treat with dopamine antagonists. Evidence even shows Metoclopramide and Aspirin combo improves nausea and vomiting in migraines better and with few side effects than Sumatriptan. Triptans have lower oral bioavailability during an acute migraine attack because of decreased gastric motility.