Drug interactions
Fluconazole + Promethazine
Severity: Major
Fluconazole and Promethazine: 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
Both drugs can prolong the QT interval, and fluconazole may also modestly inhibit CYP enzymes involved in drug metabolism. The combination may increase the risk of torsades de pointes, especially with electrolyte disturbances or high fluconazole doses.
What this interaction means in plain words
Fluconazole and Promethazine 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.
Fluconazole belongs to Anti Fungals; Promethazine belongs to Respiratory.
Why it happens
Additive QT prolongation, with possible fluconazole CYP inhibition raising promethazine exposure.
What to do
Avoid the combination where an alternative exists; otherwise check ECG and correct potassium and magnesium before and during therapy.
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 Promethazine
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Promethazine + Thioridazine Contraindicated
- Alfentanil + Promethazine Major
- Amiodarone + Promethazine Major
- Amisulpride + Promethazine Major
Other interactions of Fluconazole
- Dihydroergotamine intranasal + Fluconazole Contraindicated
- Dihydroergotamine + Fluconazole Contraindicated
- Dofetilide + Fluconazole Contraindicated
- Domperidone + Fluconazole Contraindicated
- Dronedarone + Fluconazole Contraindicated
- Erythromycin + Fluconazole Contraindicated
Frequently asked questions
Can I take Fluconazole with Promethazine?
MediHelp rates the interaction as major. Fluconazole and Promethazine 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. Both drugs can prolong the QT interval, and fluconazole may also modestly inhibit CYP enzymes involved in drug metabolism. The combination may increase the risk of torsades de pointes, especially with electrolyte disturbances or high fluconazole doses.
How serious is the interaction between Fluconazole and Promethazine?
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 where an alternative exists; otherwise check ECG and correct potassium and magnesium before and during therapy.
What other medicines interact with Promethazine?
MediHelp also lists interactions of Promethazine with, for example, Ibutilide, Pimozide, Thioridazine. The full list is on the Promethazine page.
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