Does Ondansetron Interact With Phenytoin?
In patients treated with potent inducers of CYP3A4 (i.e., phenytoin, carbamazepine, and rifampin), the clearance of ondansetron was significantly increased and ondansetron blood concentrations were decreased.
Severity: Minor
Severity basis: drug interactions section. Combining Ondansetron (5-HT3 antiemetic) and Phenytoin (Anticonvulsant) is classified as a minor interaction.
What to Do
This is generally a minor interaction, but review it with your pharmacist to be sure it is safe for you.
How This Interaction Works
Interactions like this one can happen when two medicines have overlapping effects, or when one changes how the other is absorbed, broken down, or cleared from the body. Ondansetron is a 5-ht3 antiemetic and Phenytoin is a anticonvulsant; together they are documented as a minor interaction. How much this matters depends on your dose, your other medications, and your overall health.
If You Take Both Medications
If you have been prescribed both Ondansetron and Phenytoin, do not start, stop, or change either medication on your own — some medicines are unsafe to stop suddenly. Tell your prescriber and pharmacist that you take both so they can decide whether the combination is right for you, adjust the dose, monitor you more closely, or suggest an alternative.
From the FDA Label
In patients treated with potent inducers of CYP3A4 (i.e., phenytoin, carbamazepine, and rifampin), the clearance of ondansetron was significantly increased and ondansetron blood concentrations were decreased.
Source: FDA structured product labeling (set_id 00327696-c496-4c83-a63e-9e29fd6246d4).
Check these against your full medication list in our free Interaction Checker
Frequently Asked Questions
Can you take Ondansetron and Phenytoin together?
Ondansetron and Phenytoin have a documented minor interaction. This is generally a minor interaction, but review it with your pharmacist to be sure it is safe for you.
How serious is the Ondansetron and Phenytoin interaction?
It is classified as a minor interaction, based on the FDA label's drug interactions section. A minor interaction is usually limited in effect but is still worth discussing with your care team.
What should I do if I'm taking both Ondansetron and Phenytoin?
If you have been prescribed both Ondansetron and Phenytoin, do not start, stop, or change either medication on your own — some medicines are unsafe to stop suddenly. Tell your prescriber and pharmacist that you take both so they can decide whether the combination is right for you, adjust the dose, monitor you more closely, or suggest an alternative.
This information is educational — not medical advice.
This page is provided for general educational purposes and summarizes publicly available data from sources such as the U.S. Food & Drug Administration. It is not a substitute for the judgment of a licensed clinician and should not be used to start, stop, or change any medication. It may be incomplete or out of date, and individual circumstances vary. Always talk with your prescriber or pharmacist about your specific medications and health conditions. If you think you may have a medical emergency, call 911.
Other Ondansetron Interactions
Other Phenytoin Interactions
- Phenytoin + Apixaban(major)
- Phenytoin + Itraconazole(major)
- Phenytoin + Methotrexate(major)
- Phenytoin + Rifampin(major)
- Phenytoin + Rivaroxaban(major)
- Phenytoin + Ticagrelor(major)
- Phenytoin + Amiodarone(moderate)
- Phenytoin + Atorvastatin(moderate)
- Phenytoin + Carbamazepine(moderate)
- Phenytoin + Carbidopa Levodopa(moderate)
- Phenytoin + Cholecalciferol(moderate)
- Phenytoin + Clarithromycin(moderate)
- Phenytoin + Cyclosporine(moderate)
- Phenytoin + Diazepam(moderate)
- Phenytoin + Digoxin(moderate)
- Phenytoin + Doxycycline(moderate)
- Phenytoin + Fluconazole(moderate)
- Phenytoin + Fluoxetine(moderate)
- Phenytoin + Folic Acid(moderate)
- Phenytoin + Furosemide(moderate)
- Phenytoin + Glimepiride(moderate)
- Phenytoin + Hydrocodone Acetaminophen(moderate)
- Phenytoin + Ketoconazole(moderate)
- Phenytoin + Lamotrigine(moderate)
- Phenytoin + Lithium(moderate)
- Phenytoin + Methylphenidate(moderate)
- Phenytoin + Methylprednisolone(moderate)
- Phenytoin + Mirtazapine(moderate)
- Phenytoin + Nifedipine(moderate)
- Phenytoin + Omeprazole(moderate)
- Phenytoin + Oxycodone(moderate)
- Phenytoin + Paroxetine(moderate)
- Phenytoin + Quetiapine(moderate)
- Phenytoin + Sertraline(moderate)
- Phenytoin + Simvastatin(moderate)
- Phenytoin + Tacrolimus(moderate)
- Phenytoin + Topiramate(moderate)
- Phenytoin + Tramadol(moderate)
- Phenytoin + Trazodone(moderate)
- Phenytoin + Sulfamethoxazole Trimethoprim(moderate)
- Phenytoin + Verapamil(moderate)
- Phenytoin + Warfarin(moderate)
- Phenytoin + Alprazolam(minor)
- Phenytoin + Atomoxetine(minor)
- Phenytoin + Azithromycin(minor)
- Phenytoin + Buprenorphine Naloxone(minor)
- Phenytoin + Bupropion(minor)
- Phenytoin + Canagliflozin(minor)
- Phenytoin + Clonazepam(minor)
- Phenytoin + Codeine(minor)
- Phenytoin + Dexamethasone(minor)
- Phenytoin + Gabapentin(minor)
- Phenytoin + Glipizide(minor)
- Phenytoin + Levothyroxine(minor)
- Phenytoin + Liothyronine(minor)
- Phenytoin + Metformin(minor)
- Phenytoin + Metronidazole(minor)
- Phenytoin + Modafinil(minor)
- Phenytoin + Pregabalin(minor)
- Phenytoin + Sucralfate(minor)
- Phenytoin + Tadalafil(minor)
- Phenytoin + Valproic Acid(minor)