Ondansetron

Brand Names: Zofran

Drug Class: Serotonin 5-HT3 receptor antagonist / Antiemetic

Overview

Ondansetron is a selective serotonin 5-HT3 receptor antagonist used to prevent nausea and vomiting associated with chemotherapy, radiotherapy, and postoperative recovery. It works by blocking serotonin receptors in the gastrointestinal tract and central nervous system that trigger the vomiting reflex.

Mechanism of Action

Selective serotonin 5-HT3 receptor antagonist that blocks serotonin binding at receptors in the gastrointestinal tract and chemoreceptor trigger zone, inhibiting the vomiting reflex.

Indications

  • Prevention of nausea and vomiting associated with highly emetogenic cancer chemotherapy (e.g., cisplatin ≥50 mg/m²)
  • Prevention of nausea and vomiting associated with moderately emetogenic cancer chemotherapy
  • Prevention of nausea and vomiting associated with radiotherapy (total body irradiation, single high-dose abdominal fraction, or daily abdominal fractions)
  • Prevention of postoperative nausea and/or vomiting

Common Doses

  • 4 mg
  • 8 mg
  • 24 mg

Dosage

Dosage varies by indication: Typically 8-24 mg orally in divided doses for chemotherapy-induced nausea/vomiting, 8 mg before anesthesia for postoperative prevention, and 8 mg 1-2 hours before radiotherapy. Maximum single IV dose should not exceed 16 mg due to QT prolongation risk.

Contraindications

  • Hypersensitivity to ondansetron or any component of the formulation
  • Concomitant use with apomorphine (risk of profound hypotension and loss of consciousness)

Side Effects

  • Headache
  • Constipation
  • Diarrhea
  • Fatigue
  • Dizziness
  • QT prolongation (especially with IV doses)
  • Serotonin syndrome (agitation, confusion, tachycardia, hyperreflexia)
  • Hypersensitivity reactions
  • Extrapyramidal symptoms

Interactions

  • Apomorphine: Contraindicated due to hypotension risk
  • Other QT-prolonging drugs (antiarrhythmics, antipsychotics, antibiotics): Increased risk of torsades de pointes
  • Serotonergic drugs (SSRIs, SNRIs, tramadol, MAOIs): Increased serotonin syndrome risk

Counseling Points

  • Take as prescribed before chemotherapy, radiation, or surgery
  • Report severe constipation, irregular heartbeat, or signs of allergic reaction
  • Avoid driving if experiencing dizziness or fatigue
  • Inform healthcare provider of all medications, especially heart medications or antidepressants
  • Do not take with apomorphine