How often should Zofran (ondansetron) be taken?

Zofran (Ondansetron) Dosing Frequency

For chemotherapy-induced nausea and vomiting, ondansetron 8 mg should be taken twice daily (every 12 hours), with the first dose given 30 minutes before chemotherapy. 1, 2

Dosing by Clinical Indication

Chemotherapy-Induced Nausea/Vomiting

Moderate Emetic Risk Chemotherapy:

• 8 mg orally twice daily (every 12 hours), starting 30 minutes before chemotherapy 1, 2
• Continue for 1-2 days after chemotherapy completion 3
• Alternative: 8 mg IV (0.15 mg/kg) if oral route unavailable 1

High Emetic Risk Chemotherapy:

• 8 mg orally twice daily (every 12 hours), starting 30 minutes before chemotherapy 1
• Should be combined with dexamethasone and NK1 receptor antagonists for optimal control 1
• For cisplatin-containing regimens, some protocols used 8 mg every 8 hours for 7 doses, though this is not the current standard 3

Low Emetic Risk Chemotherapy:

• 8 mg orally twice daily on day of chemotherapy only 1
• No subsequent day dosing typically required 1

Radiation-Induced Nausea/Vomiting

High-Risk Radiation Therapy:

• 8 mg orally or IV before radiation, then every 8 hours 1
• Continue for 1-2 days after completion of radiation therapy 1

Total Body Irradiation or Upper Abdomen Radiation:

• 8 mg twice daily to three times daily depending on radiation schedule 3
• For single high-dose fraction: 8 mg 1-2 hours before radiation, then every 8 hours for 3 days 2

Postoperative Nausea/Vomiting

• 16 mg as a single dose given 1 hour before induction of anesthesia 2
• This is not a repeated dosing regimen 2

Important Dosing Considerations

Maximum Daily Dose:

• Do not exceed 32 mg per day 2
• For breakthrough nausea, can titrate up to 16 mg oral or IV daily maximum 1

Timing is Critical:

• First dose must be given at least 30 minutes before chemotherapy to allow for absorption (peak concentration occurs 0.5-2 hours after oral ingestion) 4

Duration of Therapy:

• For moderately emetogenic chemotherapy: Continue for 1-2 days after chemotherapy 3
• For highly emetogenic chemotherapy: May continue for 2-3 days after chemotherapy 3

Common Pitfalls to Avoid

Do Not Use Three Times Daily Dosing for Moderate Emetic Risk:

• The FDA label explicitly states that 8 mg three times daily is NOT a recommended regimen for moderately emetogenic chemotherapy 2
• Studies showed twice daily dosing (8 mg every 12 hours) was equally effective as three times daily for cyclophosphamide-based regimens 2

Refractory Nausea:

• If nausea persists despite scheduled ondansetron, add a dopamine antagonist (metoclopramide 10-20 mg every 6-8 hours or prochlorperazine 10 mg every 6 hours) rather than increasing ondansetron frequency 3
• Consider switching to a different 5-HT3 antagonist or adding dexamethasone if not already prescribed 3

Combination Therapy:

• Ondansetron is significantly more effective when combined with dexamethasone 1
• For highly emetogenic chemotherapy, triple therapy (ondansetron + dexamethasone + NK1 antagonist) provides superior control 1

Special Populations

Elderly Patients:

• No dosage adjustment required despite decreased clearance and increased bioavailability with aging 4
• Use standard adult dosing 4

Hepatic Impairment:

• Dosage adjustments only necessary in severe hepatic impairment 4
• Since 95% is eliminated by hepatic metabolism, monitor closely in severe liver disease 4

Pediatric Patients:

• Dosing ranges from 4 mg to 8 mg three times daily depending on age (4 mg for <12 years, 8 mg for ≥12 years) 2

Administration Tips

Food Effects:

• Bioavailability is slightly increased when taken with food, but this is not clinically significant 4
• Can be taken with or without food 4

Alternative Formulations:

• Oral dissolving tablets, oral soluble film, and IV formulations all use 8 mg as standard dose 1
• Rectal, subcutaneous, and intramuscular routes have been studied but are not FDA-approved 4