Drug interactions
Promethazine + Quinacrine
Severity: Moderate
Promethazine and Quinacrine: moderate 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
Quinacrine may inhibit CYP2D6, the main enzyme responsible for promethazine hydroxylation, so promethazine exposure could rise. This could increase sedation, anticholinergic effects and QT-related risk. Quinacrine itself has been associated with CNS effects, which may compound this.
What this interaction means in plain words
Promethazine and Quinacrine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Why it happens
Possible inhibition of CYP2D6-mediated metabolism of promethazine by quinacrine.
What to do
Monitor for excessive sedation and anticholinergic effects, and consider a lower promethazine dose. Check ECG if other QT-prolonging drugs are also used.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Promethazine
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Promethazine + Thioridazine Contraindicated
- Alfentanil + Promethazine Major
- Amiodarone + Promethazine Major
- Amisulpride + Promethazine Major
Frequently asked questions
Can I take Promethazine with Quinacrine?
MediHelp rates the interaction as moderate. Promethazine and Quinacrine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Quinacrine may inhibit CYP2D6, the main enzyme responsible for promethazine hydroxylation, so promethazine exposure could rise. This could increase sedation, anticholinergic effects and QT-related risk. Quinacrine itself has been associated with CNS effects, which may compound this.
How serious is the interaction between Promethazine and Quinacrine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor for excessive sedation and anticholinergic effects, and consider a lower promethazine dose. Check ECG if other QT-prolonging drugs are also used.
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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