What is the recommended dosage and frequency of ondansetron (Zofran) for preventing nausea and vomiting in adults and children undergoing chemotherapy?

Ondansetron Dosage and Frequency for Chemotherapy-Induced Nausea and Vomiting

For adults undergoing chemotherapy, ondansetron should be administered at 8 mg intravenously or 16-24 mg orally once daily, given 30 minutes before chemotherapy starts, with subsequent doses based on the emetogenic potential of the chemotherapy regimen. 1, 2

Adult Dosing Recommendations

Highly Emetogenic Chemotherapy

• A single 24 mg oral dose administered 30 minutes before the start of single-day highly emetogenic chemotherapy, including cisplatin ≥50 mg/m² 2
• Alternatively, 8 mg IV dose can be administered 30-60 minutes before chemotherapy 1

Moderately Emetogenic Chemotherapy

• 8 mg administered 30 minutes before the start of chemotherapy, with a subsequent 8 mg dose 8 hours after the first dose, then 8 mg twice daily (every 12 hours) for 1-2 days after completion of chemotherapy 2
• For oral administration, total daily dose of 16-24 mg is recommended 1

Pediatric Dosing Recommendations

Moderately Emetogenic Chemotherapy

• 12-17 years of age: 8 mg administered 30 minutes before chemotherapy, with a subsequent 8 mg dose 8 hours after the first dose, then 8 mg twice daily for 1-2 days after completion of chemotherapy 2
• 4-11 years of age: 4 mg administered 30 minutes before chemotherapy, with subsequent 4 mg doses at 4 and 8 hours after the first dose, then 4 mg three times daily for 1-2 days after completion of chemotherapy 2

Route of Administration

• For routine use, oral doses are recommended (Level of Evidence: I, Grade of Recommendation: A) 1
• If a patient has active nausea and vomiting, treatment should be given intravenously 1
• Standard IV dose of ondansetron is 8 mg 1

Special Considerations

Hepatic Impairment

• In patients with severe hepatic impairment (Child-Pugh score of 10 or greater), do not exceed a total daily dose of 8 mg 2

Combination Therapy

• Ondansetron is often combined with dexamethasone for enhanced antiemetic effect 1, 3
• For refractory nausea and vomiting, adding dopamine antagonists to serotonin antagonists and corticosteroids is recommended (Level of Evidence: V, Grade of Recommendation: D) 1

Timing of Administration

• Antiemetics should be given prophylactically 30-60 minutes before the start of chemotherapy 1
• For delayed emesis (1-2 days after chemotherapy), continuing ondansetron administration may be necessary 1

Common Pitfalls and Caveats

• Ondansetron alone may be insufficient for highly emetogenic chemotherapy regimens; combination therapy with dexamethasone and/or aprepitant is often required 1
• Headache and constipation are common side effects of ondansetron 4, 5
• The efficacy of ondansetron may decrease with repeated chemotherapy cycles; alternative or additional antiemetics may be needed 5
• For patients with breakthrough nausea and vomiting despite prophylaxis, rescue antiemetics from a different class should be considered 6

Evidence Quality

• The recommendations for ondansetron dosing are supported by high-quality evidence (Level I, Grade A) from multiple clinical guidelines 1
• Clinical trials have demonstrated that once-daily dosing of 24 mg is as effective as, if not more effective than, multiple daily doses for highly emetogenic chemotherapy 7
• The 8 mg twice-daily regimen has shown efficacy in preventing nausea and vomiting associated with moderately emetogenic chemotherapy 8