Drug interactions
Efavirenz + Warfarin
Severity: Moderate
Efavirenz and Warfarin: 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 may change warfarin exposure and anticoagulant effect in an unpredictable direction. This can result in either subtherapeutic anticoagulation or bleeding.
What this interaction means in plain words
Efavirenz and Warfarin 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; Warfarin belongs to Cardiovascular.
Why it happens
Efavirenz induces CYP enzymes, including CYP3A4, that metabolize warfarin, but it can also inhibit CYP2C9, so the net effect is variable.
What to do
Check the INR more often when efavirenz is started, changed or stopped. Adjust the warfarin dose to keep the INR in range.
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 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 Warfarin
- Defibrotide + Warfarin Contraindicated
- Ketorolac + Warfarin Contraindicated
- Abciximab + Warfarin Major
- Acetylsalicylic acid + Warfarin Major
- Adagrasib + Warfarin Major
- Amiodarone + Warfarin Major
Frequently asked questions
Can I take Efavirenz with Warfarin?
MediHelp rates the interaction as moderate. Efavirenz and Warfarin 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 may change warfarin exposure and anticoagulant effect in an unpredictable direction. This can result in either subtherapeutic anticoagulation or bleeding.
How serious is the interaction between Efavirenz and Warfarin?
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 the INR more often when efavirenz is started, changed or stopped. Adjust the warfarin dose to keep the INR in range.
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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