GI

Antiemetics

Gastrointestinal

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Examples

ondansetronpromethazinemetoclopramidescopolamine

Prefix / Suffix: -setron (5-HT3 antagonists)

Physiology

Vomiting is triggered by the chemoreceptor trigger zone (CTZ) and vestibular system via multiple receptors (serotonin, dopamine, histamine, muscarinic).

Mechanism of Action

Different classes block specific receptors: 5-HT3 antagonists (ondansetron) block serotonin; dopamine antagonists (metoclopramide, promethazine) block D2; antihistamines/anticholinergics (scopolamine) block H1/muscarinic.

Indications

  • Chemotherapy-induced nausea/vomiting
  • Postoperative nausea/vomiting
  • Motion sickness
  • Pregnancy nausea (selected agents)

Side Effects / Adverse Effects

  • Headache (ondansetron)
  • QT prolongation (ondansetron — risk of arrhythmias)
  • Sedation (promethazine, scopolamine)
  • Extrapyramidal symptoms (metoclopramide, promethazine)
  • Dry mouth (scopolamine)

Contraindications

  • Long QT syndrome (ondansetron)
  • Bowel obstruction (metoclopramide)

Nursing Considerations

  • Monitor ECG with ondansetron (QT prolongation risk)
  • Assess for extrapyramidal symptoms with metoclopramide (tremor, rigidity)
  • Give 30 minutes before chemo or meals (preventive use)
  • Monitor hydration (vomiting causes fluid loss)
  • Caution with sedating types (driving / falls in elderly)

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Disclaimer: PharmPal Nurse is for education only and is not medical advice. Do not use it to diagnose, treat, prescribe, or make patient-care decisions; always verify with current drug references, your instructor, facility policy, and a licensed provider. In emergencies, call local emergency services.