What is the dosing frequency of Zofran (ondansetron) 8mg for preventing nausea and vomiting?

Ondansetron 8mg Dosing Frequency

Ondansetron 8mg should be administered twice daily (every 12 hours) for moderately emetogenic chemotherapy, with the first dose given 30 minutes before chemotherapy and continued for 1-2 days after completion. 1, 2

Standard Dosing by Clinical Context

Moderately Emetogenic Chemotherapy

• Administer 8mg orally twice daily, with the first dose 30 minutes before chemotherapy, followed by a second dose 8 hours later, then 8mg twice daily for 2 days after chemotherapy completion 2
• This twice-daily regimen demonstrated 61% complete response (no emetic episodes) in placebo-controlled trials 2, 3
• Combination with dexamethasone 12mg significantly enhances efficacy compared to ondansetron monotherapy 1

Highly Emetogenic Chemotherapy (Cisplatin ≥50mg/m²)

• A single 24mg oral dose once daily is superior to 8mg twice daily for highly emetogenic regimens 2, 4
• The 24mg once-daily regimen achieved 66% complete response versus 55% with 8mg twice daily 2, 4
• The 8mg twice-daily regimen is not recommended for highly emetogenic chemotherapy 2
• Triple therapy (ondansetron + NK1 antagonist + dexamethasone) is mandatory for optimal control 1

Low Emetogenic Chemotherapy

• 8mg orally twice daily on the day of chemotherapy only, with no subsequent day dosing required 1

Radiation-Induced Nausea and Vomiting

• 8mg orally or IV every 8 hours for high-risk radiation therapy, starting before each radiation fraction 1
• Continue for 1-2 days after completion of radiation therapy 1
• For moderate-risk radiation, 8mg once daily before radiation on treatment days only 1

Intravenous Dosing

• 8mg IV (or 0.15mg/kg) is the standard intravenous dose, given as a single dose 30 minutes before chemotherapy 5, 1
• Maximum single IV dose is 16mg due to cardiac safety concerns (QT prolongation risk) 1

Key Clinical Considerations

Timing and Duration

• Always administer the first dose 30 minutes before the emetogenic stimulus (chemotherapy or radiation) 1, 2
• For moderately emetogenic chemotherapy, continue for 1-2 days post-treatment 1, 2
• For highly emetogenic chemotherapy, continue for 2-3 days post-treatment when using the 24mg once-daily regimen 1

Refractory Nausea Management

• If nausea persists despite scheduled ondansetron, add a dopamine antagonist (metoclopramide 20-30mg three to four times daily or prochlorperazine) to the regimen 5, 1
• Consider titrating ondansetron up to a maximum of 16mg oral or IV daily for breakthrough symptoms 1
• Switching to a different 5-HT3 antagonist or adding dexamethasone (if not already prescribed) are alternative strategies 1

Common Pitfalls to Avoid

• Do not use 8mg twice daily for highly emetogenic chemotherapy—this is inadequate; use 24mg once daily instead 2, 4
• Do not use 8mg three times daily—this regimen is not recommended and offers no advantage over twice-daily dosing 2
• Do not exceed 16mg as a single IV dose due to cardiac arrhythmia risk 1
• Do not use ondansetron monotherapy for moderate-to-high emetogenic risk—always combine with dexamethasone for superior efficacy 1

Special Populations

• In severe hepatic impairment (Child-Pugh ≥10), ondansetron clearance is reduced 2-3 fold with half-life increasing to 20 hours; dose adjustment may be necessary 2