Drug interactions
Efavirenz + Toremifene
Severity: Major
Efavirenz and Toremifene: 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
Both drugs prolong the QT interval, and combining them can increase the risk of torsades de pointes. Efavirenz may also reduce toremifene levels through enzyme induction, which could weaken its effect.
What this interaction means in plain words
Efavirenz and Toremifene 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.
Efavirenz belongs to Anti Virals; Toremifene belongs to Endocrine.
Why it happens
Additive QT prolongation plus CYP3A4 induction by efavirenz, which increases toremifene clearance.
What to do
Avoid the combination where possible and use a non-QT-prolonging antiretroviral. If unavoidable, monitor ECG and electrolytes and watch for reduced toremifene efficacy.
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 Efavirenz
- Cobimetinib + Efavirenz Contraindicated
- Dienogest / estradiol valerate + Efavirenz Contraindicated
- Dihydroergotamine intranasal + Efavirenz Contraindicated
- Dihydroergotamine + Efavirenz Contraindicated
- Doravirine + Efavirenz Contraindicated
- Efavirenz + Elbasvir / grazoprevir Contraindicated
Other interactions of Toremifene
- Amiodarone + Toremifene Contraindicated
- Dronedarone + Toremifene Contraindicated
- Nilotinib + Toremifene Contraindicated
- Pimozide + Toremifene Contraindicated
- Quinidine + Toremifene Contraindicated
- Ribociclib + Toremifene Contraindicated
Frequently asked questions
Can I take Efavirenz with Toremifene?
MediHelp rates the interaction as major. Efavirenz and Toremifene 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 prolong the QT interval, and combining them can increase the risk of torsades de pointes. Efavirenz may also reduce toremifene levels through enzyme induction, which could weaken its effect.
How serious is the interaction between Efavirenz and Toremifene?
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 possible and use a non-QT-prolonging antiretroviral. If unavoidable, monitor ECG and electrolytes and watch for reduced toremifene efficacy.
What other medicines interact with Efavirenz?
MediHelp also lists interactions of Efavirenz with, for example, Cobimetinib, Dienogest / estradiol valerate, Dihydroergotamine intranasal. The full list is on the Efavirenz page.
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