Drug interactions
Phenytoin + Quetiapine
Severity: Major
Phenytoin and Quetiapine: 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 strongly induces CYP3A4 and substantially lowers quetiapine concentrations, risking loss of psychiatric control. The effect reverses when phenytoin is stopped, which can lead to quetiapine accumulation.
What this interaction means in plain words
Phenytoin and Quetiapine 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 belongs to Central Nervous System; Quetiapine belongs to Central Nervous System.
Why it happens
Induction of CYP3A4 by phenytoin increases quetiapine clearance.
What to do
Expect to need a considerably higher quetiapine dose and monitor clinical response. If phenytoin is withdrawn, reduce quetiapine gradually and watch for sedation and hypotension.
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 Quetiapine
- Adagrasib + Quetiapine Major
- Amiodarone + Quetiapine Major
- Amisulpride + Quetiapine Major
- Amoxapine + Quetiapine Major
- Anagrelide + Quetiapine Major
- Apalutamide + Quetiapine 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 Phenytoin with Quetiapine?
MediHelp rates the interaction as major. Phenytoin and Quetiapine 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 strongly induces CYP3A4 and substantially lowers quetiapine concentrations, risking loss of psychiatric control. The effect reverses when phenytoin is stopped, which can lead to quetiapine accumulation.
How serious is the interaction between Phenytoin and Quetiapine?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Expect to need a considerably higher quetiapine dose and monitor clinical response. If phenytoin is withdrawn, reduce quetiapine gradually and watch for sedation and hypotension.
What other medicines interact with Quetiapine?
MediHelp also lists interactions of Quetiapine with, for example, Adagrasib, Amiodarone, Amisulpride. The full list is on the Quetiapine page.
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