What is the dose and duration of Zofran (ondansetron) for nausea and vomiting?

Ondansetron Dosing and Duration for Nausea and Vomiting

For chemotherapy-induced nausea and vomiting, administer ondansetron 8 mg IV or 16-24 mg orally as a single dose 30 minutes before chemotherapy, with continuation based on the emetogenic potential of the regimen—typically 8 mg orally every 8-12 hours for 2-3 days after chemotherapy. 1, 2

Route and Initial Dosing

• Intravenous administration: The standard IV dose is 8 mg given 30-60 minutes before chemotherapy starts 3, 1
• Oral administration: For routine prophylaxis, oral dosing is preferred (16-24 mg as a single dose or 8 mg) 1, 2
• Active nausea/vomiting: If the patient is already experiencing nausea and vomiting, switch to IV administration 1

Duration Based on Chemotherapy Emetogenicity

Highly Emetogenic Chemotherapy (e.g., cisplatin ≥50 mg/m²)

• Day 1: Single 24 mg oral dose 30 minutes before chemotherapy 2
• Days 2-5: Continue 8 mg orally every 8 hours for up to 7 doses after chemotherapy 3
• Note: The 24 mg single oral dose showed 66% complete response rates (no emetic episodes) in clinical trials 2

Moderately Emetogenic Chemotherapy (e.g., cyclophosphamide-doxorubicin)

• Day 1: 8 mg orally 30 minutes before chemotherapy, then 8 mg again 8 hours later 2
• Days 2-3: Continue 8 mg orally twice daily (every 12 hours) for 2 days after chemotherapy completion 2, 4
• Clinical evidence: This regimen achieved 61% complete response rates versus 6% with placebo 2, 5

Low Emetogenic Chemotherapy

• Single dose: 8 mg orally before chemotherapy may be sufficient 1
• No routine prophylaxis after day 1 is typically needed 3

Combination Therapy Considerations

• Always combine with dexamethasone for enhanced antiemetic effect—dexamethasone 10-20 mg IV on day 1, then 4-8 mg orally twice daily for delayed emesis 3, 1
• For refractory cases: Add dopamine antagonists (metoclopramide or prochlorperazine) to the ondansetron-dexamethasone combination 3, 1
• Highly emetogenic regimens: Consider adding aprepitant (NK1 antagonist) to the combination 1

Delayed Emesis Management (Days 2-5)

• Oral ondansetron maintenance is effective for preventing delayed nausea and vomiting, with 60% complete response rates versus 42% with placebo 4
• Continue 8 mg orally every 12 hours for 2-3 days after chemotherapy 4, 5
• Efficacy is maintained over multiple courses of chemotherapy 4

Postoperative Nausea and Vomiting

• Single dose: 16 mg orally given 1 hour before induction of anesthesia 2
• Note: Clinical trials were conducted primarily in female patients undergoing inpatient surgical procedures 2

Common Pitfalls and Caveats

• Ondansetron monotherapy is insufficient for highly emetogenic chemotherapy—always use combination therapy with dexamethasone 1
• The 8 mg three times daily regimen is NOT recommended for moderately emetogenic chemotherapy despite being studied; twice daily dosing is equally effective and improves compliance 2, 5
• The 32 mg single dose is NOT recommended due to lack of additional benefit over 24 mg and increased QT prolongation risk 2
• Breakthrough nausea/vomiting: Use rescue antiemetics from a different drug class (dopamine antagonists like metoclopramide 10 mg every 6 hours) rather than increasing ondansetron dose 3, 1
• Hepatic impairment: Maximum daily dose should not exceed 8 mg in patients with severe hepatic impairment (Child-Pugh ≥10) due to prolonged half-life (20 hours versus 7 hours) 2

Rescue Therapy for Inadequate Control

• Inpatient setting: Ondansetron 8 mg IV bolus followed by 1 mg/hour continuous infusion 3
• Add lorazepam 1 mg orally every 1 hour as needed for anticipatory nausea 3