What is the appropriate dosage of Zofran (ondansetron) for adults with nausea?

Appropriate Dosage of Ondansetron (Zofran) for Adult Nausea

For adults with nausea, the recommended dosage of ondansetron (Zofran) is 8 mg orally twice daily as needed. 1

Dosing Guidelines

• The standard oral dose of ondansetron for treating nausea in adults is 8 mg taken twice daily as needed 1
• For breakthrough nausea, ondansetron can be administered as 8 mg orally (tablet, oral dissolving tablet, or oral soluble film) 2
• When used as an antiemetic for chemotherapy-induced nausea, ondansetron may be administered at 8 mg orally every 8-12 hours 2
• For medication-induced nausea, the "as needed" (prn) approach is generally more appropriate than scheduled dosing 3

Administration Routes

• Oral administration is preferred for outpatient management of nausea 1
• Available oral formulations include:
  • Standard tablets (8 mg) 1
  • Oral dissolving tablets (8 mg) 1
  • Oral soluble film (8 mg) 1
• Intravenous administration (8 mg or 0.15 mg/kg IV) may be considered when oral administration is not feasible due to severe vomiting 2, 4

Efficacy

• Ondansetron has demonstrated significant efficacy in reducing nausea scores by a mean of 4.0 points on a 10-point scale 4
• Intravenous administration provides the most rapid relief with the largest improvements in nausea scores (mean 4.4), followed by intramuscular (mean 3.6) and oral dissolving tablets (mean 3.3) 4
• Twice daily oral dosing has shown comparable efficacy to three times daily dosing in clinical trials 5

Alternative Antiemetics

If ondansetron is ineffective or contraindicated, consider these alternatives:

• Prochlorperazine: 5-10 mg orally every 6 hours as needed 2, 3
• Metoclopramide: 5-20 mg orally every 6-8 hours as needed 2, 3
• Dexamethasone: 4 mg orally or IV for refractory cases 3

Adverse Effects and Precautions

• Common side effects include headache (24%), constipation (9%), and diarrhea (6%) 1
• Less common side effects include dizziness, anxiety, and urinary retention 1
• Rare but serious adverse effects include:
  • QT interval prolongation and cardiac arrhythmias 1
  • Serotonin syndrome when combined with other serotonergic medications 1
• Dose adjustments should be considered in patients with hepatic impairment 1
• For patients with renal impairment with creatinine clearance between 20-50 mL/min, consider reducing the dose 2

Special Considerations

• For persistent nausea, consider switching from as-needed dosing to scheduled dosing 3
• Ensure adequate hydration, as dehydration can worsen nausea 3
• If nausea persists despite ondansetron therapy, consider adding an agent from a different drug class 2
• For medication-induced nausea (such as from hydrochlorothiazide), taking ondansetron before the causative medication may help prevent symptoms 3