What is the prescribed dose of ondansetron (Zofran) for nausea and vomiting?

Ondansetron Dosing for Nausea and Vomiting

The standard dosage of ondansetron for nausea and vomiting is 8 mg orally administered once to three times daily, with alternative IV administration of 8 mg when oral administration is not feasible. 1

Dosing Guidelines by Route of Administration

Oral Administration

• Standard dosing: 8 mg orally 1-3 times daily 1
• For chemotherapy-induced nausea and vomiting:
  • Highly emetogenic chemotherapy: 24 mg as a single dose 30 minutes before chemotherapy 2
  • Moderately emetogenic chemotherapy: 8 mg twice daily for 3 days 2, 3
  • First dose should be given 30 minutes before chemotherapy, with subsequent dose 8 hours later 2

Intravenous Administration

• Standard IV dose: 8 mg 4, 1
• Administration timing: 30-60 minutes before start of chemotherapy 4
• For breakthrough symptoms: IV administration is preferred when a patient already has nausea and vomiting 4

Dosing for Specific Clinical Scenarios

Chemotherapy-Induced Nausea and Vomiting

• Highly emetogenic chemotherapy: 24 mg oral single dose or 8 mg IV 1, 2
• Moderately emetogenic chemotherapy: 8 mg twice daily for 3 days 2, 3
• Radiation therapy: 8 mg oral twice daily 1
• Total body irradiation: 8 mg oral 2-3 times daily 1

Postoperative Nausea and Vomiting

• Optimal dose: 4 mg IV for treatment of established postoperative nausea and vomiting 5

General Nausea and Vomiting

• As needed dosing: 8 mg oral or IV every 8-12 hours 1

Special Considerations

Combination Therapy

• For enhanced efficacy in highly emetogenic chemotherapy, combine ondansetron with:
  • Dexamethasone (20 mg IV/PO) 1
  • NK1 receptor antagonists (e.g., aprepitant) 1

Dosage Adjustments

• Hepatic dysfunction: Consider dose reduction in severe hepatic impairment 1
• Renal dysfunction: No specific dose adjustment mentioned in guidelines

Administration Tips

• For oral administration, medication can be taken with or without food
• For IV administration, administer over 2-5 minutes
• For breakthrough symptoms, IV administration is preferred 4

Common Pitfalls to Avoid

1. Inadequate dosing: Ensure appropriate dose based on severity of nausea/vomiting and emetogenic potential of treatment
2. Inappropriate timing: Administer 30-60 minutes before chemotherapy for prophylaxis 4
3. Monotherapy for highly emetogenic stimuli: Combine with dexamethasone and/or NK1 antagonists for highly emetogenic chemotherapy 1
4. Excessive dosing: FDA has concerns about doses of 32 mg IV due to potential QT interval prolongation 6

Ondansetron is highly effective for nausea and vomiting with a favorable safety profile when used at appropriate doses. The efficacy is comparable to other 5-HT3 receptor antagonists such as granisetron and tropisetron 7.