Drug interactions
Fosphenytoin + Simvastatin
Severity: Moderate
Fosphenytoin and Simvastatin: 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 CYP3A4 inducer that can lower simvastatin plasma concentrations and weaken its cholesterol-lowering effect. This is a loss-of-efficacy interaction rather than a toxicity risk, so it does not warrant a contraindication.
What this interaction means in plain words
Fosphenytoin and Simvastatin 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; Simvastatin belongs to Cardiovascular.
Why it happens
Phenytoin induces CYP3A4, increasing the metabolism of simvastatin and its active acid.
What to do
Monitor LDL cholesterol after starting or stopping fosphenytoin and increase the statin dose or switch to a less CYP3A4-dependent statin such as rosuvastatin or pravastatin if control is lost.
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?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Fosphenytoin and Simvastatin, the additional notes, the evidence detail and the whole-prescription interaction checker.
- Full clinical management advice
- Additional notes
- Evidence detail
- Interaction checker for a whole prescription
Try Pro+ free for 7 days on the web. No card needed.
Other interactions of Simvastatin
- Atazanavir + Simvastatin Contraindicated
- Clarithromycin + Simvastatin Contraindicated
- Cobicistat + Simvastatin Contraindicated
- Cyclosporin + Simvastatin Contraindicated
- Danazol + Simvastatin Contraindicated
- Darunavir + Simvastatin Contraindicated
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 Simvastatin?
MediHelp rates the interaction as moderate. Fosphenytoin and Simvastatin 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 CYP3A4 inducer that can lower simvastatin plasma concentrations and weaken its cholesterol-lowering effect. This is a loss-of-efficacy interaction rather than a toxicity risk, so it does not warrant a contraindication.
How serious is the interaction between Fosphenytoin and Simvastatin?
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 LDL cholesterol after starting or stopping fosphenytoin and increase the statin dose or switch to a less CYP3A4-dependent statin such as rosuvastatin or pravastatin if control is lost.
What other medicines interact with Simvastatin?
MediHelp also lists interactions of Simvastatin with, for example, Atazanavir, Clarithromycin, Cobicistat. The full list is on the Simvastatin page.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.
