Drug interactions
Fosphenytoin + Sodium valproate
Severity: Major
Fosphenytoin and Sodium valproate: 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
Valproate displaces phenytoin from protein binding and inhibits its metabolism, changing free phenytoin levels. The combination has also been linked to hyperammonemia and encephalopathy.
What this interaction means in plain words
Fosphenytoin and Sodium valproate 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 belongs to Central Nervous System; Sodium valproate belongs to Central Nervous System.
Why it happens
Protein-binding displacement and metabolic inhibition alter phenytoin exposure, and valproate impairs ammonia detoxification.
What to do
Monitor free phenytoin concentrations and ammonia if there is lethargy or confusion, adjusting doses as needed.
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?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Fosphenytoin and Sodium valproate, 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 14 days on the web. No card needed.
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
Other interactions of Sodium valproate
Frequently asked questions
Can I take Fosphenytoin with Sodium valproate?
MediHelp rates the interaction as major. Fosphenytoin and Sodium valproate 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. Valproate displaces phenytoin from protein binding and inhibits its metabolism, changing free phenytoin levels. The combination has also been linked to hyperammonemia and encephalopathy.
How serious is the interaction between Fosphenytoin and Sodium valproate?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor free phenytoin concentrations and ammonia if there is lethargy or confusion, adjusting doses as needed.
What other medicines interact with Fosphenytoin?
MediHelp also lists interactions of Fosphenytoin with, for example, Dronedarone, Ledipasvir-sofosbuvir, Lorlatinib. The full list is on the Fosphenytoin 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.
