Drug interactions
Fosphenytoin + Risperidone
Severity: Moderate
Fosphenytoin and Risperidone: moderate 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, the active form of fosphenytoin, induces CYP3A4 and P-glycoprotein and can lower risperidone and 9-hydroxyrisperidone concentrations. This may lead to loss of antipsychotic effect and relapse.
What this interaction means in plain words
Fosphenytoin and Risperidone can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Fosphenytoin belongs to Central Nervous System; Risperidone belongs to Central Nervous System.
Why it happens
Induction of CYP3A4 and P-glycoprotein by phenytoin, increasing risperidone clearance.
What to do
Monitor for loss of psychiatric control and increase the risperidone dose if needed; reduce the dose again if phenytoin is stopped.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Risperidone
- Ibutilide + Risperidone Contraindicated
- Risperidone + Vandetanib Contraindicated
- Adagrasib + Risperidone Major
- Amiodarone + Risperidone Major
- Amisulpride + Risperidone Major
- Amoxapine + Risperidone Major
Other interactions of Fosphenytoin
- Dronedarone + Fosphenytoin Contraindicated
- Fosphenytoin + Ledipasvir-sofosbuvir Contraindicated
- Fosphenytoin + Lorlatinib Contraindicated
- Fosphenytoin + Lurasidone Contraindicated
- Fosphenytoin + Ranolazine Contraindicated
- Fosphenytoin + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
Frequently asked questions
Can I take Fosphenytoin with Risperidone?
MediHelp rates the interaction as moderate. Fosphenytoin and Risperidone can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Phenytoin, the active form of fosphenytoin, induces CYP3A4 and P-glycoprotein and can lower risperidone and 9-hydroxyrisperidone concentrations. This may lead to loss of antipsychotic effect and relapse.
How serious is the interaction between Fosphenytoin and Risperidone?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor for loss of psychiatric control and increase the risperidone dose if needed; reduce the dose again if phenytoin is stopped.
What other medicines interact with Risperidone?
MediHelp also lists interactions of Risperidone with, for example, Ibutilide, Vandetanib, Adagrasib. The full list is on the Risperidone page.
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