Drug interactions
Thioridazine + Tolterodine
Severity: Major
Thioridazine and Tolterodine: 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
Thioridazine strongly prolongs the QT interval, inhibits CYP2D6 and has marked anticholinergic activity. With tolterodine, risks of QT prolongation, torsades de pointes and anticholinergic toxicity are increased.
What this interaction means in plain words
Thioridazine and Tolterodine 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.
Thioridazine belongs to Central Nervous System; Tolterodine belongs to Genitourinary.
Why it happens
Additive QT prolongation and antimuscarinic effects, plus CYP2D6 inhibition by thioridazine raising tolterodine exposure.
What to do
Avoid the combination and choose an alternative bladder agent with less QT effect. If unavoidable, monitor the ECG and electrolytes and use the lowest tolterodine 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 Tolterodine
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 Thioridazine with Tolterodine?
MediHelp rates the interaction as major. Thioridazine and Tolterodine 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. Thioridazine strongly prolongs the QT interval, inhibits CYP2D6 and has marked anticholinergic activity. With tolterodine, risks of QT prolongation, torsades de pointes and anticholinergic toxicity are increased.
How serious is the interaction between Thioridazine and Tolterodine?
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 choose an alternative bladder agent with less QT effect. If unavoidable, monitor the ECG and electrolytes and use the lowest tolterodine dose.
What other medicines interact with Tolterodine?
MediHelp also lists interactions of Tolterodine with, for example, Clarithromycin, Clozapine, Cobicistat. The full list is on the Tolterodine page.
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