What is the recommended dosage for Zofran (ondansetron)?

Ondansetron Dosing Recommendations

Chemotherapy-Induced Nausea and Vomiting (CINV)

For highly emetogenic chemotherapy, ondansetron should be dosed as a single 24 mg oral dose or 8-16 mg IV on day 1 before chemotherapy, with continuation of other antiemetics (NK1 antagonists and dexamethasone) on subsequent days. 1

High Emetogenic Risk Chemotherapy (e.g., cisplatin, AC regimens)

Day 1 dosing options:

• Oral: Single 24 mg dose administered by tablets, oral dissolving tablets, or oral dissolving film before chemotherapy 1
• IV: 8 mg or 0.15 mg/kg IV 1
• Alternative oral: 16-24 mg PO once 1

Days 2-4: Ondansetron is typically NOT continued; other antiemetics (dexamethasone ± NK1 antagonist) are used instead 2

Moderate Emetogenic Risk Chemotherapy

Day 1 dosing:

• Oral: 8 mg twice daily or 16 mg once 1, 3
• IV: 8 mg or 0.15 mg/kg 1

Days 2-3: Continue ondansetron 8 mg twice daily 2, 4

The twice-daily regimen (8 mg every 12 hours) is equally effective as three-times-daily dosing and improves compliance 5. Maintenance ondansetron after 24 hours significantly reduces delayed nausea and vomiting compared to placebo (complete response 59.6% vs 42.1%, P=0.012). 4

Low Emetogenic Risk Chemotherapy

• Single 8 mg dose before chemotherapy 2
• Additional doses only as rescue therapy for breakthrough symptoms 2

Multi-Day Chemotherapy Regimens

• Administer ondansetron daily during chemotherapy and for 2 days thereafter 2

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Radiation-Induced Nausea and Vomiting

High-Risk Radiation (Total Body Irradiation)

• 8 mg oral or IV once to twice daily on days of radiation therapy, starting before the first fraction 1
• Continue once daily on the day after each radiation treatment 2

Moderate-Risk Radiation (Upper abdomen, craniospinal)

• 8 mg oral or IV once daily before radiation therapy 1
• Continue once daily on the day after each radiation treatment if no radiation planned 1

Low-Risk Radiation (Brain, head/neck, thorax, pelvis)

• 8 mg oral or IV as rescue therapy only 1
• For brain radiation: use dexamethasone as primary prophylaxis if not already taking corticosteroids 1

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Postoperative Nausea and Vomiting (PONV)

For adult females undergoing surgery, ondansetron 16 mg as a single oral dose should be given 1 hour before induction of anesthesia. 3

Pediatric Dosing

For children receiving chemotherapy:

• IV: 0.15 mg/kg (or 5 mg/m²) per dose 6
• Multiple doses may be given every 4-8 hours as needed 6

For pediatric postoperative nausea:

• IV: 0.1-0.15 mg/kg, which is superior to droperidol or metoclopramide 6

Combining ondansetron with dexamethasone significantly improves efficacy in children receiving chemotherapy. 6

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Rescue Therapy for Breakthrough Symptoms

• Titrate up as needed to a maximum of 16 mg oral or IV daily 1
• Can be administered every 8 hours for breakthrough symptoms 1

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Key Clinical Considerations

Important Caveats

• The 24 mg single IV dose is NOT recommended due to increased risk of QT prolongation; use 8-16 mg IV instead 1
• Oral dolasetron should only be used at 100 mg (not IV for CINV) 1
• When ondansetron is combined with aprepitant or other NK1 antagonists, dexamethasone doses must be reduced by 50% due to CYP3A4 interactions 1

Transaminase Elevations

• Clinically significant transaminase elevations occur more frequently with high-dose cisplatin (AST 6.5%, ALT 5.0%) compared to moderate-dose regimens 7
• Monitor liver function tests in patients receiving high-dose chemotherapy 7

Schedule Flexibility

• The schedule of ondansetron in the first 24 hours (single dose vs. multiple doses) does not significantly influence efficacy for moderately emetogenic chemotherapy 4
• Twice-daily oral dosing is as effective as three-times-daily and improves patient compliance 5