Drug interactions
Cimetidine + Thioridazine
Severity: Major
Cimetidine and Thioridazine: 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
Cimetidine can increase thioridazine concentrations, which raises the risk of dose-related QT prolongation and torsades de pointes. Thioridazine has a serious cardiac toxicity profile.
What this interaction means in plain words
Cimetidine and Thioridazine 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 belongs to Gastrointestinal Tract; Thioridazine belongs to Central Nervous System.
Why it happens
Cimetidine inhibits CYP2D6, decreasing thioridazine clearance.
What to do
Avoid the combination and use famotidine or a PPI instead. If it cannot be avoided, monitor ECG QTc and electrolytes.
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 Cimetidine
- Cimetidine + Dofetilide Contraindicated
- Cimetidine + Fezolinetant Contraindicated
- Alfentanil + Cimetidine Major
- Atazanavir + Cimetidine Major
- Carmustine + Cimetidine Major
- Cimetidine + Citalopram Major
Other interactions of Thioridazine
- Abiraterone + Thioridazine Contraindicated
- Adagrasib + Thioridazine Contraindicated
- Amiodarone + Thioridazine Contraindicated
- Amisulpride + Thioridazine Contraindicated
- Amitriptyline + Thioridazine Contraindicated
- Amoxapine + Thioridazine Contraindicated
Frequently asked questions
Can I take Cimetidine with Thioridazine?
MediHelp rates the interaction as major. Cimetidine and Thioridazine 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 can increase thioridazine concentrations, which raises the risk of dose-related QT prolongation and torsades de pointes. Thioridazine has a serious cardiac toxicity profile.
How serious is the interaction between Cimetidine and Thioridazine?
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 use famotidine or a PPI instead. If it cannot be avoided, monitor ECG QTc and electrolytes.
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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