Drug interactions
Fosphenytoin + Tolbutamide
Severity: Minor
Fosphenytoin and Tolbutamide: minor 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, which is highly protein bound and can compete with tolbutamide for binding and also inhibit insulin secretion. Tolbutamide control may weaken, and phenytoin levels may shift, but effects are typically small.
What this interaction means in plain words
Fosphenytoin and Tolbutamide have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Fosphenytoin belongs to Central Nervous System; Tolbutamide belongs to Endocrine.
Why it happens
Competition for plasma protein binding and phenytoin-related suppression of insulin release; phenytoin may also induce tolbutamide metabolism.
What to do
Monitor blood glucose and phenytoin levels when starting or stopping the combination, adjusting tolbutamide as needed.
What to ask your pharmacist
- Is there anything I should notice while taking both?
- Do I need to tell my doctor at the next visit?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Fosphenytoin and Tolbutamide, 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 Tolbutamide
- Glyburide-metformin + Tolbutamide Major
- Insulin degludec-liraglutide + Tolbutamide Major
- Aceclofenac + Tolbutamide Moderate
- Acemetacin + Tolbutamide Moderate
- Acetylsalicylic acid + Tolbutamide Moderate
- Albiglutide + Tolbutamide Moderate
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 Tolbutamide?
MediHelp rates the interaction as minor. Fosphenytoin and Tolbutamide have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Fosphenytoin is converted to phenytoin, which is highly protein bound and can compete with tolbutamide for binding and also inhibit insulin secretion. Tolbutamide control may weaken, and phenytoin levels may shift, but effects are typically small.
How serious is the interaction between Fosphenytoin and Tolbutamide?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor blood glucose and phenytoin levels when starting or stopping the combination, adjusting tolbutamide as needed.
What other medicines interact with Tolbutamide?
MediHelp also lists interactions of Tolbutamide with, for example, Glyburide-metformin, Insulin degludec-liraglutide, Aceclofenac. The full list is on the Tolbutamide 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.
