How should I take ondansetron (Zofran) for nausea and vomiting?

How to Take Ondansetron Orally Disintegrating Tablets (ODT) for Nausea

For general nausea management, take ondansetron 8 mg ODT every 8 hours as needed, placing the tablet on your tongue and allowing it to dissolve without water. 1, 2

Proper Administration Technique

• Place the tablet directly on your tongue and allow it to dissolve completely—swallowing is not necessary, and water is not required for administration 3, 4
• The tablet will disintegrate within seconds and can be swallowed with saliva 4
• Ondansetron should be taken at least 30 minutes before a known trigger (such as chemotherapy or radiation) for optimal preventive effect 5

Standard Dosing Intervals

• Every 8 hours is the recommended interval for scheduled dosing when nausea is persistent 1, 2
• For breakthrough nausea (as-needed use), you can take 8 mg and repeat every 8 hours, with a maximum of 16 mg in 24 hours for general nausea management 1, 2
• The medication reaches peak blood levels 0.5 to 2 hours after oral administration, with effects lasting approximately 3.8 hours 5

When to Switch from As-Needed to Scheduled Dosing

• If you require ondansetron more than twice in 24 hours, switch to scheduled around-the-clock dosing (8 mg every 8 hours) for at least 24-48 hours to prevent the cycle of breakthrough symptoms 1
• Scheduled dosing is more effective than repeated as-needed dosing for persistent nausea 1

What to Do If Ondansetron Doesn't Work

• Do not simply take more ondansetron—instead, add a medication with a different mechanism of action 1
• Contact your healthcare provider to add metoclopramide (10-20 mg every 6-8 hours) or prochlorperazine (5-10 mg every 6-8 hours) to your ondansetron regimen 1
• The combination of ondansetron plus a dopamine antagonist (like metoclopramide) addresses nausea through two different pathways and is more effective than increasing ondansetron alone 1

Important Considerations and Side Effects

• Ondansetron can cause constipation, which may paradoxically worsen nausea if not addressed—ensure adequate hydration and consider a stool softener if taking ondansetron for more than 2-3 days 1
• The medication is generally well tolerated, with headache being the most common side effect (along with constipation) 6, 7
• Avoid exceeding 16 mg in a single dose due to cardiac safety concerns related to QT interval prolongation 2

Context-Specific Dosing

• For radiation-induced nausea: Take 8 mg 2-3 times daily on days you receive radiation, continuing for 1-2 days after completion 8, 1
• For chemotherapy-induced nausea: Dosing depends on the type of chemotherapy—for moderately emetogenic chemotherapy, take 8 mg twice daily starting before chemotherapy and continuing for 1-2 days after 1, 3
• For postoperative nausea: A single 16 mg dose taken 1 hour before surgery is effective for prevention 3

When Ondansetron May Not Be the Best First Choice

• For general nausea unrelated to chemotherapy, radiation, or surgery, dopamine antagonists like metoclopramide or prochlorperazine are recommended as first-line treatment and are more cost-effective than ondansetron 1
• Ondansetron works best for nausea caused by serotonin release (chemotherapy, radiation, surgery) rather than other causes like gastroenteritis or medication side effects 1