What is a typical prescription for Zofran (ondansetron)?

Typical Zofran (Ondansetron) Prescription

For chemotherapy-induced nausea and vomiting, prescribe ondansetron 8 mg orally twice daily or 8 mg IV (0.15 mg/kg), starting 30 minutes before chemotherapy, with continuation for 1-3 days post-treatment depending on emetogenic risk. 1, 2

Standard Dosing by Clinical Context

Chemotherapy-Induced Nausea/Vomiting

Moderately Emetogenic Chemotherapy:

• 8 mg PO twice daily or 8 mg IV (0.15 mg/kg, max 16 mg) 1, 2
• First dose: 30 minutes before chemotherapy 2, 3
• Continue for 1-2 days after chemotherapy completion 2
• Often combined with dexamethasone 12 mg PO/IV for enhanced efficacy 1

Highly Emetogenic Chemotherapy:

• 16-24 mg PO once daily or 8-16 mg IV once daily 1
• Must be combined with NK1 receptor antagonist (aprepitant 125 mg or fosaprepitant 150 mg) plus dexamethasone 12 mg 1, 2
• Continue for 2-3 days post-chemotherapy 2
• The 32 mg IV single dose is no longer recommended due to QT prolongation risk 4

Low Emetogenic Chemotherapy:

• 8 mg PO twice daily or 8 mg IV on day of chemotherapy only 1, 2
• No subsequent day dosing typically required 2

Radiation-Induced Nausea/Vomiting

High-Risk Radiation (upper abdomen, total body irradiation):

• 8 mg PO or IV before each radiation fraction 1, 2
• Continue daily on radiation days, plus 1-2 days after completion 1, 2
• For total body irradiation: 8 mg administered 1.5 hours before each fraction 5

Moderate-Risk Radiation (pelvis, thorax):

• 8 mg PO once daily before radiation 1
• Use as prophylaxis on radiation days only 1

Postoperative Nausea/Vomiting

• 16 mg PO as single dose given 1 hour before anesthesia induction 5
• Alternative: 4 mg IV at induction or end of surgery 5

Available Formulations

• Oral tablets: 4 mg, 8 mg 5
• Oral dissolving tablets (ODT): 4 mg, 8 mg 1
• Oral soluble film: 4 mg, 8 mg 1
• Injectable: 2 mg/mL (typically dosed as 8 mg or 0.15 mg/kg IV) 1, 5

Breakthrough/Rescue Dosing

If nausea persists despite scheduled ondansetron:

• Titrate up to maximum 16 mg oral or IV daily 1, 2
• Add dopamine antagonist: metoclopramide 10-20 mg or prochlorperazine 10 mg 1, 2
• Consider adding dexamethasone 4-12 mg if not already prescribed 2
• May switch to alternative 5-HT3 antagonist (granisetron, palonosetron) 2

Critical Prescribing Considerations

Combination Therapy is Superior:

• Ondansetron alone is less effective than combination regimens 6, 7
• For moderate-to-high emetogenic risk, always combine with dexamethasone 1, 6
• For highly emetogenic chemotherapy, triple therapy (ondansetron + NK1 antagonist + dexamethasone) is mandatory 1, 2

Cardiac Safety:

• Avoid 32 mg IV dose due to QT prolongation and torsades de pointes risk 4
• Use caution in patients with pre-existing cardiac conduction abnormalities 4
• Maximum recommended single IV dose is 16 mg 1

Timing Matters:

• Administer at least 30 minutes before emetogenic stimulus 2, 3
• Peak concentration occurs 0.5-2 hours after oral administration 3
• For radiation: give 1-2 hours before treatment 5

Common Pitfalls:

• Underdosing for highly emetogenic chemotherapy (must use triple therapy, not ondansetron alone) 1, 2
• Failing to continue dosing for 1-3 days post-chemotherapy (delayed nausea is common) 2
• Using ondansetron monotherapy when combination therapy is indicated 1, 7
• Prescribing 32 mg IV dose (contraindicated due to cardiac risk) 4

Special Populations:

• Pediatric: 0.15 mg/kg IV (max 16 mg) or 4-8 mg PO based on body surface area 5, 6
• Elderly: No dose adjustment required despite altered pharmacokinetics 3
• Severe hepatic impairment: Maximum 8 mg daily 3
• Renal impairment: No adjustment needed (95% hepatic metabolism) 3

Adverse Effects:

• Most common: headache (9-27%), constipation (6-11%) 6, 7
• Generally well-tolerated; adverse events rarely require discontinuation 6, 7