Drug interactions
Fosphenytoin + Sofosbuvir-velpatasvir
Severity: Major
Fosphenytoin and Sofosbuvir-velpatasvir: major interaction.
Last updated Sources: US FDA label
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, which is converted to phenytoin, is an inducer of CYP enzymes and P-gp. It can substantially reduce sofosbuvir and velpatasvir levels and cause HCV treatment failure.
What this interaction means in plain words
Fosphenytoin and Sofosbuvir-velpatasvir 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; Sofosbuvir-velpatasvir belongs to Anti Virals.
Why it happens
Phenytoin induces P-gp and CYP2B6, CYP2C8 and CYP3A4, increasing clearance of both antivirals.
What to do
Avoid the combination and switch to a non-inducing anticonvulsant such as levetiracetam where possible. Otherwise defer HCV therapy.
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 Sofosbuvir-velpatasvir, 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.
References
Other interactions of Sofosbuvir-velpatasvir
- Rifampin + Sofosbuvir-velpatasvir Contraindicated
- Rifapentine + Sofosbuvir-velpatasvir Contraindicated
- Sofosbuvir-velpatasvir + St john's wort Contraindicated
- Amiodarone + Sofosbuvir-velpatasvir Major
- Apalutamide + Sofosbuvir-velpatasvir Major
- Carbamazepine + Sofosbuvir-velpatasvir 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 Sofosbuvir-velpatasvir?
MediHelp rates the interaction as major. Fosphenytoin and Sofosbuvir-velpatasvir 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, which is converted to phenytoin, is an inducer of CYP enzymes and P-gp. It can substantially reduce sofosbuvir and velpatasvir levels and cause HCV treatment failure.
How serious is the interaction between Fosphenytoin and Sofosbuvir-velpatasvir?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid the combination and switch to a non-inducing anticonvulsant such as levetiracetam where possible. Otherwise defer HCV therapy.
What other medicines interact with Sofosbuvir-velpatasvir?
MediHelp also lists interactions of Sofosbuvir-velpatasvir with, for example, Rifampin, Rifapentine, St john's wort. The full list is on the Sofosbuvir-velpatasvir 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.
