A World Without Ondansetron

Nausea and vomiting are not one syndrome: GI, vestibular, chemoreceptor-trigger-zone, and brain-gut axis patterns respond to different receptor targets. When ondansetron is unavailable or not ideal, matching the antiemetic to the physiology is often more useful than reflexively reaching for a single drug.

Cause-Directed Antiemetic Selection

• Four emesis phenotypes: A practical four-bucket model—gastrointestinal, vestibular, brainstem, and brain-gut axis—helps match antiemetics to the dominant receptor biology instead of treating all vomiting as the same problem.
• Gastrointestinal pathway targeting: GI vomiting reflects vagal activation plus serotonin and dopamine signaling, so ondansetron and metoclopramide are common first-line choices, with prochlorperazine as another option.
• Vestibular mechanism focus: Vertigo-driven nausea is a histamine and muscarinic problem, making meclizine, diphenhydramine, and scopolamine better fits than serotonin-first strategies.
• Brainstem trigger zone: Chemoreceptor trigger zone nausea from toxins, medications, DKA, or hyperemesis gravidarum involves mixed dopamine, serotonin, histamine, and muscarinic input; trimethobenzamide is a useful alternative with less QT concern.
• Brain-gut axis syndromes: Cyclic vomiting and related syndromes behave more like central sensitization states, where haloperidol, droperidol, or olanzapine may outperform routine ondansetron. We get into the bedside pattern recognition in the episode.
• Bridge therapy pearl: Isopropyl alcohol swabs can provide fast bedside relief while IV access is being obtained, a low-tech move that is easy to forget in busy ED nausea care.

Safety Pearls and QT Risk

• No routine pre-dose EKG: Routine EKG screening before antiemetics is unnecessary in low-risk patients; a quick chart review for long QT history, electrolyte problems, or interacting drugs is usually enough.
• Medication risk review: Antipsychotics, antiarrhythmics, macrolides, fluoroquinolones, antidepressants, methadone, and other antiemetics are the medication classes most likely to compound QT risk.
• Condition-based QT flags: Long QT syndrome, hypocalcemia, hypokalemia, hypomagnesemia, hypothyroidism, and hypothermia are the major clinical red flags that should change how casually you give QT-active agents.
• Prior EKG value: An old EKG is often more informative than reflexive new testing, especially when it shows the patient's baseline QT before the current illness and medication stack.
• Repeat-dose caution: Risk rises when patients need multiple antiemetic doses or several agents from different classes. We walk through when that should push you toward more monitoring in the chapter.

References:

1. Farkas J. Nausea, emesis, and antiemetics. EMCrit Project. Published August 17, 2020. Accessed July 6, 2023. https://emcrit.org/ibcc/antiemetic/
2. Furyk JS, et al. Drugs for the treatment of nausea and vomiting in adults in the emergency department setting. Cochrane Database Syst Rev. 2015;2015(9):CD010106. Published 2015 Sep 28. PMID: 26411330
3. Repanshek Z. Vomiting in a World Without Ondansetron Zachary Repanshek, MD FAAEM. www.youtube.com. Published 2018. Accessed July 6, 2023. https://www.youtube.com/watch?v=cewLtoKRzb0
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9. Shahsavari D, et al. Haloperidol Use in the Emergency Department for Gastrointestinal Symptoms: Nausea, Vomiting, and Abdominal Pain. Clin Transl Gastroenterol. 2021;12(6):e00362. Published 2021 Jun 1.  PMID: 34060494
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