What is the oral (PO) dose of Zofran (ondansetron)?

Ondansetron (Zofran) Oral Dosing Guidelines

The standard oral (PO) dose of ondansetron (Zofran) is 8 mg taken every 8-12 hours, with a maximum daily dose of 24 mg for most indications. 1

Dosing Based on Clinical Scenario

Chemotherapy-Induced Nausea and Vomiting

• Highly Emetogenic Chemotherapy:

  • 24 mg PO as a single dose 30 minutes before chemotherapy 2, 1
  • Alternative: 8 mg PO 30 minutes before chemotherapy, followed by 8 mg PO 8 hours later 1

• Moderately Emetogenic Chemotherapy:

  • 8 mg PO 30 minutes before chemotherapy, followed by 8 mg PO 8 hours later, then 8 mg PO twice daily for 1-2 days after completion of chemotherapy 2, 1
  • Alternative: 16-24 mg PO once daily 2

• Low Emetogenic Chemotherapy:

  • 8 mg PO twice daily as needed 2

Radiation-Induced Nausea and Vomiting

• 8 mg PO 1-2 hours before radiation therapy, then 8 mg PO every 8 hours as needed 1
• For total body irradiation: 8 mg PO 1.5 hours before each fraction of radiotherapy 1

Postoperative Nausea and Vomiting

• 16 mg PO as a single dose 1 hour before induction of anesthesia 1

Special Populations

Pediatric Patients (4-18 years)

• 4-8 mg PO three times daily based on weight and age 1
• Children <12 years: 4 mg PO three times daily
• Children ≥12 years: 8 mg PO three times daily

Elderly Patients

• No specific dose adjustment required despite slightly decreased clearance and increased bioavailability 3

Hepatic Impairment

• Severe impairment: Consider lower doses or less frequent dosing
• Maximum daily dose should not exceed 8 mg 1

Administration Pearls

• Oral ondansetron should be administered at least 30 minutes before the emetogenic stimulus (chemotherapy, radiation, etc.) for optimal efficacy 3
• Bioavailability of oral ondansetron is approximately 60% compared to IV administration due to first-pass metabolism 3
• Taking ondansetron with food slightly increases bioavailability but does not significantly impact clinical efficacy 3
• Ondansetron reaches peak concentration 0.5-2 hours after oral ingestion 3

Safety Considerations

• Monitor for QT prolongation, particularly with higher doses (>32 mg IV equivalent) 4
• Common side effects include headache and constipation
• Avoid in patients with congenital long QT syndrome
• Use caution when combining with other QT-prolonging medications

Clinical Pearls

• Combination therapy with dexamethasone significantly improves antiemetic efficacy compared to ondansetron alone 5
• For breakthrough nausea and vomiting, consider adding an agent from a different drug class rather than increasing ondansetron dose 2
• Effectiveness of ondansetron is maintained over multiple courses of chemotherapy 5
• Alternative formulations include IV, sublingual, and transdermal patches for patients unable to tolerate oral medications 2