Drug interactions
Olanzapine / samidorphan + Phenytoin
Severity: Major
Olanzapine / samidorphan and Phenytoin: major 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 substantially lowers olanzapine and samidorphan exposure, which can cause loss of antipsychotic control.
What this interaction means in plain words
Olanzapine / samidorphan and Phenytoin can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Why it happens
CYP3A4 induction by phenytoin (with induction of other pathways such as UGT/CYP1A2 for olanzapine) increases clearance of both components.
What to do
Avoid concurrent use per labeling and consider a non-inducing anticonvulsant. If unavoidable, monitor psychiatric symptoms closely.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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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 Olanzapine / samidorphan with Phenytoin?
MediHelp rates the interaction as major. Olanzapine / samidorphan and Phenytoin can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Phenytoin substantially lowers olanzapine and samidorphan exposure, which can cause loss of antipsychotic control.
How serious is the interaction between Olanzapine / samidorphan and Phenytoin?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid concurrent use per labeling and consider a non-inducing anticonvulsant. If unavoidable, monitor psychiatric symptoms closely.
What other medicines interact with Phenytoin?
MediHelp also lists interactions of Phenytoin with, for example, Artemether / lumefantrine, Bictegravir, Cabotegravir. The full list is on the Phenytoin page.
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