Drug interactions
Efavirenz + Promethazine
Severity: Moderate
Efavirenz and Promethazine: 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
Efavirenz can prolong the QT interval, particularly at higher exposure, and promethazine has some QT-prolonging potential. Together they may increase the risk of ventricular arrhythmia, and both can cause CNS effects such as dizziness and drowsiness.
What this interaction means in plain words
Efavirenz and Promethazine 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.
Efavirenz belongs to Anti Virals; Promethazine belongs to Respiratory.
Why it happens
Additive QT prolongation and CNS effects.
What to do
Check baseline ECG and electrolytes in patients with other QT risk factors and correct potassium and magnesium. Monitor for dizziness, sedation and palpitations.
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 Efavirenz
- Cobimetinib + Efavirenz Contraindicated
- Dienogest / estradiol valerate + Efavirenz Contraindicated
- Dihydroergotamine intranasal + Efavirenz Contraindicated
- Dihydroergotamine + Efavirenz Contraindicated
- Doravirine + Efavirenz Contraindicated
- Efavirenz + Elbasvir / grazoprevir Contraindicated
Frequently asked questions
Can I take Efavirenz with Promethazine?
MediHelp rates the interaction as moderate. Efavirenz and Promethazine 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. Efavirenz can prolong the QT interval, particularly at higher exposure, and promethazine has some QT-prolonging potential. Together they may increase the risk of ventricular arrhythmia, and both can cause CNS effects such as dizziness and drowsiness.
How serious is the interaction between Efavirenz and Promethazine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Check baseline ECG and electrolytes in patients with other QT risk factors and correct potassium and magnesium. Monitor for dizziness, sedation and palpitations.
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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