Drug interactions
Ondansetron + Phenytoin
Severity: Minor
Ondansetron and Phenytoin: minor interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Phenytoin induces hepatic enzymes and increases ondansetron clearance, lowering its levels. This may reduce antiemetic efficacy, though the change is typically modest.
What this interaction means in plain words
Ondansetron and Phenytoin have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Ondansetron belongs to Gastrointestinal Tract; Phenytoin belongs to Central Nervous System.
Why it happens
Induction of CYP3A4 and other hepatic enzymes by phenytoin accelerates ondansetron metabolism.
What to do
No routine dose change is advised; assess nausea control and consider an alternative or additional antiemetic if response is poor.
What to ask your pharmacist
- Is there anything I should notice while taking both?
- Do I need to tell my doctor at the next visit?
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Other interactions of Ondansetron
- Apomorphine + Ondansetron Contraindicated
- Ondansetron + Thioridazine Contraindicated
- Ondansetron + Vandetanib Contraindicated
- Adagrasib + Ondansetron Major
- Amiodarone + Ondansetron Major
- Amisulpride + Ondansetron Major
Other interactions of Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Frequently asked questions
Can I take Ondansetron with Phenytoin?
MediHelp rates the interaction as minor. Ondansetron and Phenytoin have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Phenytoin induces hepatic enzymes and increases ondansetron clearance, lowering its levels. This may reduce antiemetic efficacy, though the change is typically modest.
How serious is the interaction between Ondansetron and Phenytoin?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: No routine dose change is advised; assess nausea control and consider an alternative or additional antiemetic if response is poor.
What other medicines interact with Ondansetron?
MediHelp also lists interactions of Ondansetron with, for example, Apomorphine, Thioridazine, Vandetanib. The full list is on the Ondansetron page.
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