Drug interactions
Promethazine + Ritonavir
Severity: Moderate
Promethazine and Ritonavir: 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
Ritonavir is a potent inhibitor of CYP3A4 and also inhibits CYP2D6, and may raise promethazine concentrations. Higher exposure may cause more sedation, anticholinergic effects and, rarely, QT prolongation. Ritonavir itself can prolong the QT interval at higher exposures.
What this interaction means in plain words
Promethazine and Ritonavir 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.
Promethazine belongs to Respiratory; Ritonavir belongs to Anti Virals.
Why it happens
Ritonavir inhibits CYP2D6 and CYP3A4, reducing hepatic clearance of promethazine.
What to do
Monitor for oversedation, hypotension and anticholinergic effects, and use the lowest effective promethazine dose. Consider an ECG when other QT-prolonging drugs are co-prescribed.
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
Other interactions of Ritonavir
- Alfuzosin + Ritonavir Contraindicated
- Amiodarone + Ritonavir Contraindicated
- Avanafil + Ritonavir Contraindicated
- Colchicine + Ritonavir Contraindicated
- Dronedarone + Ritonavir Contraindicated
- Eletriptan + Ritonavir Contraindicated
Frequently asked questions
Can I take Promethazine with Ritonavir?
MediHelp rates the interaction as moderate. Promethazine and Ritonavir 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. Ritonavir is a potent inhibitor of CYP3A4 and also inhibits CYP2D6, and may raise promethazine concentrations. Higher exposure may cause more sedation, anticholinergic effects and, rarely, QT prolongation. Ritonavir itself can prolong the QT interval at higher exposures.
How serious is the interaction between Promethazine and Ritonavir?
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 oversedation, hypotension and anticholinergic effects, and use the lowest effective promethazine dose. Consider an ECG when other QT-prolonging drugs are co-prescribed.
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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