What is the recommended dosage of Zofran (ondansetron) for treating nausea and vomiting?

Ondansetron (Zofran) Dosage Recommendations

For treating nausea and vomiting, ondansetron should be administered at 8 mg orally twice daily for most indications, with specific dosing adjustments based on the clinical scenario. 1, 2

Oral Dosing by Clinical Scenario

Chemotherapy-Induced Nausea and Vomiting

• For highly emetogenic chemotherapy: 24 mg as a single oral dose 30 minutes before chemotherapy 3
• For moderately emetogenic chemotherapy: 8 mg orally 30 minutes before chemotherapy, followed by 8 mg 8 hours later, then 8 mg twice daily for 1-2 days after completion of chemotherapy 3, 4
• For breakthrough nausea/vomiting: 8 mg orally every 12 hours as needed 2

Radiation-Induced Nausea and Vomiting

• For radiation to upper abdomen or total body irradiation: 8 mg orally 2-3 times daily during treatment 5
• For single high-dose fraction radiotherapy: 8 mg orally 1-2 hours before radiotherapy, then in late afternoon and at bedtime, continuing three times daily for 3 days 3
• For daily fractionated radiotherapy: 8 mg orally 1-2 hours before first daily fraction, with subsequent 8 mg doses approximately every 8 hours on each day of radiotherapy 3, 6

Postoperative Nausea and Vomiting

• For prevention: 16 mg as a single oral dose one hour before induction of anesthesia 3
• For treatment of established postoperative nausea/vomiting: 8 mg orally every 8-12 hours as needed 7

Intravenous Dosing

• Standard IV dose: 8 mg administered over 15 minutes 1
• For chemotherapy-induced nausea/vomiting: 8 mg IV 30 minutes before chemotherapy, with potential additional doses 8 hours after the first dose 1
• For breakthrough nausea in hospitalized patients: 8 mg IV bolus followed by 1 mg/hour continuous infusion may be considered 5

Special Considerations

Efficacy Considerations

• Ondansetron has shown superior efficacy compared to placebo, with 61% of patients having no emetic episodes compared to only 6% with placebo in moderately emetogenic chemotherapy 4
• For radiation therapy, ondansetron provided complete control of emesis in 67% of patients compared with 45% receiving placebo 5

Safety Considerations

• QT interval prolongation is a concern with high-dose ondansetron (32 mg IV), but this is less of a concern with standard doses 1
• Common side effects include headache (23% of patients), constipation, and diarrhea 4, 8
• The elimination half-life is approximately 3.5 hours in healthy volunteers but extended to about 7.9 hours in elderly patients 8

Refractory Cases

• For patients with inadequate response, consider:
  • Adding medications from different classes (e.g., dexamethasone, metoclopramide) 1, 2
  • Switching to a different 5-HT3 antagonist such as granisetron or palonosetron 1
  • Adding lorazepam for anticipatory nausea/vomiting 5

Pitfalls and Caveats

• The 32 mg once-daily oral dose is not recommended for prevention of nausea and vomiting associated with highly emetogenic chemotherapy due to QT prolongation risk 3
• Ondansetron 8 mg three times daily is not a recommended regimen for moderately emetogenic chemotherapy 3
• Before initiating treatment for breakthrough emesis, assess for non-chemotherapy causes such as electrolyte abnormalities, brain metastases, or GI abnormalities 5
• Antacid therapy (proton pump inhibitors, H2 blockers) should be considered if patients have dyspepsia, as patients sometimes have difficulty distinguishing heartburn from nausea 5