Drug interactions
Phenytoin + Valbenazine
Severity: Major
Phenytoin and Valbenazine: 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 can markedly reduce exposure to valbenazine and its active metabolite, which may cause loss of efficacy in tardive dyskinesia or chorea. Labeling advises against combining valbenazine with strong CYP3A4 inducers.
What this interaction means in plain words
Phenytoin and Valbenazine 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; Valbenazine belongs to Central Nervous System.
Why it happens
Phenytoin induces CYP3A4, increasing the metabolism of valbenazine and its active metabolite.
What to do
Avoid the combination and choose a different antiepileptic if feasible; otherwise monitor closely for loss of symptom control.
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
Other interactions of Valbenazine
- Deutetrabenazine + Valbenazine Contraindicated
- Tranylcypromine + Valbenazine Contraindicated
- Amiodarone + Valbenazine Major
- Amisulpride + Valbenazine Major
- Apalutamide + Valbenazine Major
- Carbamazepine + Valbenazine Major
Frequently asked questions
Can I take Phenytoin with Valbenazine?
MediHelp rates the interaction as major. Phenytoin and Valbenazine 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 can markedly reduce exposure to valbenazine and its active metabolite, which may cause loss of efficacy in tardive dyskinesia or chorea. Labeling advises against combining valbenazine with strong CYP3A4 inducers.
How serious is the interaction between Phenytoin and Valbenazine?
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 the combination and choose a different antiepileptic if feasible; otherwise monitor closely for loss of symptom control.
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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