Drug interactions
Fosphenytoin + Verapamil
Severity: Moderate
Fosphenytoin and Verapamil: 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
Fosphenytoin is converted to phenytoin, a strong CYP3A4 inducer, which can markedly lower verapamil concentrations and cause loss of blood pressure or rate control. Verapamil may also affect phenytoin levels, although this is less well characterized.
What this interaction means in plain words
Fosphenytoin and Verapamil 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; Verapamil belongs to Cardiovascular.
Why it happens
Phenytoin induces CYP3A4 and other enzymes, increasing first-pass and systemic metabolism of verapamil.
What to do
Monitor blood pressure and heart rate or arrhythmia control, and titrate verapamil upward as needed. Consider an alternative antihypertensive or rate-control agent if response is inadequate, and check phenytoin levels when verapamil is started or 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 Verapamil
- Dofetilide + Verapamil Contraindicated
- Flibanserin + Verapamil Contraindicated
- Lomitapide + Verapamil Contraindicated
- Lonafarnib + Verapamil Contraindicated
- Pimozide + Verapamil Contraindicated
- Acebutolol + Verapamil 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 Verapamil?
MediHelp rates the interaction as moderate. Fosphenytoin and Verapamil 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 is converted to phenytoin, a strong CYP3A4 inducer, which can markedly lower verapamil concentrations and cause loss of blood pressure or rate control. Verapamil may also affect phenytoin levels, although this is less well characterized.
How serious is the interaction between Fosphenytoin and Verapamil?
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 blood pressure and heart rate or arrhythmia control, and titrate verapamil upward as needed. Consider an alternative antihypertensive or rate-control agent if response is inadequate, and check phenytoin levels when verapamil is started or stopped.
What other medicines interact with Verapamil?
MediHelp also lists interactions of Verapamil with, for example, Dofetilide, Flibanserin, Lomitapide. The full list is on the Verapamil page.
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