Drug interactions
Cimetidine + Fentanyl transmucosal
Severity: Major
Cimetidine and Fentanyl transmucosal: major interaction.
Last updated Sources: UK SmPC
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
Cimetidine may increase systemic fentanyl exposure, mainly the swallowed portion. This increases the risk of sedation and respiratory depression.
What this interaction means in plain words
Cimetidine and Fentanyl transmucosal 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
Cimetidine inhibits CYP3A4 in the gut and liver, reducing fentanyl clearance.
What to do
Monitor sedation and respiratory rate frequently and adjust the fentanyl dose accordingly. Use famotidine instead of cimetidine where possible.
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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References
Other interactions of Cimetidine
- Cimetidine + Dofetilide Contraindicated
- Cimetidine + Fezolinetant Contraindicated
- Alfentanil + Cimetidine Major
- Atazanavir + Cimetidine Major
- Carmustine + Cimetidine Major
- Cimetidine + Citalopram Major
Frequently asked questions
Can I take Cimetidine with Fentanyl transmucosal?
MediHelp rates the interaction as major. Cimetidine and Fentanyl transmucosal 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. Cimetidine may increase systemic fentanyl exposure, mainly the swallowed portion. This increases the risk of sedation and respiratory depression.
How serious is the interaction between Cimetidine and Fentanyl transmucosal?
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 sedation and respiratory rate frequently and adjust the fentanyl dose accordingly. Use famotidine instead of cimetidine where possible.
What other medicines interact with Cimetidine?
MediHelp also lists interactions of Cimetidine with, for example, Dofetilide, Fezolinetant, Alfentanil. The full list is on the Cimetidine page.
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