Drug interactions
Aripiprazole + Fosphenytoin
Severity: Major
Aripiprazole and Fosphenytoin: major interaction.
Last updated Sources: UK SmPC
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
Fosphenytoin is converted to phenytoin, which induces CYP3A4 and can substantially lower aripiprazole concentrations. This may lead to loss of antipsychotic or mood-stabilizing efficacy and relapse.
What this interaction means in plain words
Aripiprazole and Fosphenytoin 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.
Aripiprazole belongs to Central Nervous System; Fosphenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induction of CYP3A4 increases aripiprazole clearance.
What to do
Labeling for strong CYP3A4 inducers advises doubling the aripiprazole dose; monitor clinical response closely. Reduce the dose back to normal within about 1-2 weeks after the inducer is stopped.
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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References
- Abilify 1 mg/mL Oral Solution - SmPC sections 4.3/4.5 (class statement: other inducers of CYP3A4; "Concomitant administration of aripiprazole and other inducers of CYP3A4 (such as rifampicin, rifabutin, phenytoin, phenobarbital, primidone, efavirenz, nevirapi") — electronic medicines compendium (UK SmPC)
Other interactions of Aripiprazole
- Aripiprazole + Pimozide Contraindicated
- Aripiprazole + Thioridazine Contraindicated
- Amisulpride + Aripiprazole Major
- Aripiprazole + Arsenic trioxide Major
- Aripiprazole + Calcium / magnesium / potassium / sodium oxybates Major
- Aripiprazole + Carbamazepine 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 Aripiprazole with Fosphenytoin?
MediHelp rates the interaction as major. Aripiprazole and Fosphenytoin 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. Fosphenytoin is converted to phenytoin, which induces CYP3A4 and can substantially lower aripiprazole concentrations. This may lead to loss of antipsychotic or mood-stabilizing efficacy and relapse.
How serious is the interaction between Aripiprazole and Fosphenytoin?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Labeling for strong CYP3A4 inducers advises doubling the aripiprazole dose; monitor clinical response closely. Reduce the dose back to normal within about 1-2 weeks after the inducer is stopped.
What other medicines interact with Aripiprazole?
MediHelp also lists interactions of Aripiprazole with, for example, Pimozide, Thioridazine, Amisulpride. The full list is on the Aripiprazole page.
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