Ondansetron (Zofran) Dosing and Use Guidelines
For prevention of nausea and vomiting, ondansetron should be dosed at 24 mg PO once daily for highly emetogenic chemotherapy and 8 mg PO twice daily for moderately emetogenic chemotherapy, with the first dose given 30 minutes before treatment. 1, 2
Dosing Recommendations by Clinical Scenario
Highly Emetogenic Chemotherapy
- Dose: 24 mg PO as a single dose 2
- Timing: Administer 30 minutes before start of chemotherapy 2
- Efficacy: 66% of patients achieve complete response (no emesis, no rescue medication) 2
- Note: 8 mg twice daily and 32 mg once daily regimens are NOT recommended for highly emetogenic chemotherapy 2
Moderately Emetogenic Chemotherapy
- Dose: 8 mg PO twice daily 1, 2
- Schedule: First dose 30 minutes before chemotherapy, second dose 8 hours later, then continue twice daily for 2 days after completion of chemotherapy 2
- Efficacy: 61% of patients experience no emetic episodes compared to only 6% with placebo 2, 3
Radiation Therapy
- Indication: Prevention of nausea/vomiting with total body irradiation or abdominal radiation 2
- Regimen: Ondansetron with or without dexamethasone based on radiation field 1
- For upper abdominal radiation: Ondansetron with or without dexamethasone, plus lorazepam 0.5-2 mg PO/IV as needed 1
Postoperative Nausea and Vomiting
- Indication: Prevention of postoperative nausea/vomiting 2
- Evidence: More effective than placebo and single-dose droperidol or metoclopramide 4
Combination Therapy Recommendations
Triple Therapy for Highly Emetogenic Chemotherapy
- Ondansetron (5-HT3 antagonist) + dexamethasone + NK1 antagonist (e.g., aprepitant) 1
- Aprepitant dosing: 125 mg PO day 1, then 80 mg PO days 2-3 1, 5
- Note: When combined with aprepitant, reduce dexamethasone dose by 50% due to drug interactions 1
Dual Therapy for Moderately Emetogenic Chemotherapy
Important Clinical Considerations
Safety Concerns
- Cardiac safety: FDA warning regarding potential QT interval prolongation with 32 mg IV dose 6
- Lower doses used for postoperative nausea/vomiting appear safer, but caution is still warranted 6
Pediatric Use
- Effective in children receiving chemotherapy at a dose of 5 mg/m² 30 minutes before chemotherapy, then 4 mg/m² every 8 hours IV 7
- More effective than tropisetron for mild to moderately emetogenic chemotherapy in children 7
Treatment Failures
- For breakthrough symptoms: Add agent from different class (prochlorperazine 10 mg PO/IV every 4-6 hours, metoclopramide 10-40 mg PO/IV every 4-6 hours, or olanzapine 2.5-5 mg PO twice daily) 1
- For anticipatory nausea/vomiting: Consider lorazepam or behavioral techniques 1
Administration Routes
- Oral and IV formulations have equivalent efficacy 1
- Route selection should be based on patient's ability to take oral medications 1
Key Principles for Optimal Use
- Prevention is more effective than treating established nausea/vomiting 1
- Timing of first dose (30 minutes before chemotherapy) is critical for efficacy 2
- Always rule out other causes of nausea/vomiting in cancer patients (infection, electrolyte disturbances, constipation, GI obstruction, brain metastases, medication side effects) 1