Drug interactions
Fentanyl transmucosal + Phenytoin
Severity: Major
Fentanyl transmucosal and Phenytoin: 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
Phenytoin can lower fentanyl concentrations, reducing analgesia and possibly causing withdrawal in opioid-dependent patients. When phenytoin is discontinued, fentanyl exposure may increase and cause respiratory depression.
What this interaction means in plain words
Fentanyl transmucosal and Phenytoin 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.
Why it happens
Phenytoin induces CYP3A4, increasing the metabolism of fentanyl.
What to do
Monitor analgesic response and titrate transmucosal fentanyl carefully. After phenytoin is stopped, monitor for sedation and respiratory depression and lower the fentanyl dose.
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?
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Other interactions of Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Frequently asked questions
Can I take Fentanyl transmucosal with Phenytoin?
MediHelp rates the interaction as major. Fentanyl transmucosal and Phenytoin 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. Phenytoin can lower fentanyl concentrations, reducing analgesia and possibly causing withdrawal in opioid-dependent patients. When phenytoin is discontinued, fentanyl exposure may increase and cause respiratory depression.
How serious is the interaction between Fentanyl transmucosal and Phenytoin?
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 analgesic response and titrate transmucosal fentanyl carefully. After phenytoin is stopped, monitor for sedation and respiratory depression and lower the fentanyl dose.
What other medicines interact with Phenytoin?
MediHelp also lists interactions of Phenytoin with, for example, Artemether / lumefantrine, Bictegravir, Cabotegravir. The full list is on the Phenytoin page.
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