Ondansetron Dosing Guidelines
For chemotherapy-induced nausea and vomiting, ondansetron is dosed at 16-24 mg PO once daily or 8-12 mg IV (maximum 32 mg/day) for prevention of acute emesis, with oral dosing of 8 mg PO twice daily or 16 mg PO once daily for delayed emesis. 1, 2
Oral Dosing
Highly Emetogenic Chemotherapy
- Single dose regimen: 24 mg PO once, administered 30 minutes before chemotherapy 3
- This regimen showed 66% of patients completing 24 hours with no emetic episodes and no rescue medications 3
- Not recommended: 8 mg PO twice daily or 32 mg PO once daily 3
Moderately Emetogenic Chemotherapy
- Initial dose: 8 mg PO 30 minutes before chemotherapy
- Subsequent doses: 8 mg PO 8 hours after first dose
- Maintenance: 8 mg PO twice daily for 1-2 days after completion of chemotherapy 3
- Alternative: 16 mg PO once daily 1, 2
Intravenous Dosing
Highly Emetogenic Chemotherapy
- Dose: 8-12 mg IV (maximum 32 mg/day) 1
- Administered 30 minutes before chemotherapy
Moderately Emetogenic Chemotherapy
- Dose: 8 mg IV 2
- Administered 30 minutes before chemotherapy
Special Populations
Hepatic Impairment
- For severe hepatic impairment (Child-Pugh score ≥10), maximum daily dose should be limited to 8 mg 3
- Patients with mild-to-moderate hepatic impairment have a 2-fold reduction in clearance and increased half-life (11.6 hours vs 5.7 hours in healthy subjects) 3
Elderly Patients
- No specific dose adjustments required despite slightly decreased clearance and increased bioavailability 4
Pharmacokinetic Considerations
- Oral bioavailability: approximately 60% 4
- Time to peak concentration: 0.5-2 hours after oral administration 4
- Elimination half-life: approximately 3.8 hours 4
- Primarily metabolized by the liver (95%) 4
- Should be administered at least 30 minutes before chemotherapy to achieve optimal antiemetic effect 4
Combination Therapy
- For optimal control of chemotherapy-induced nausea and vomiting, ondansetron is often combined with:
- Dexamethasone (12 mg PO/IV)
- NK1 antagonist (e.g., aprepitant 125 mg PO day 1,80 mg PO days 2-3) 2
Clinical Efficacy
- Complete control of vomiting in 69% of patients on day 1 and 60% on days 2-5 in non-cisplatin chemotherapy 5
- For cisplatin-based regimens, complete response (no emesis) achieved in 60% of patients 6
Ondansetron's efficacy is maintained over multiple chemotherapy cycles, with most patients (80%) preferring it to previous antiemetic regimens for non-cisplatin chemotherapy 5. The most common side effects are headache and constipation, which are generally mild and well-tolerated 5.