Drug interactions
Efavirenz + Fentanyl
Severity: Moderate
Efavirenz and Fentanyl: 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 induce CYP3A4, the main enzyme that clears fentanyl, so fentanyl concentrations may fall and analgesia may be lost. In opioid-dependent patients this can trigger withdrawal symptoms. If efavirenz is later stopped, fentanyl levels can rise again and cause excess sedation or respiratory depression.
What this interaction means in plain words
Efavirenz and Fentanyl 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; Fentanyl belongs to Musculoskeletal.
Why it happens
Efavirenz induces hepatic and intestinal CYP3A4, increasing the metabolism of fentanyl.
What to do
Monitor pain control and withdrawal signs after efavirenz is started and titrate the fentanyl dose to effect. When efavirenz is stopped, reduce the fentanyl dose and watch for sedation and respiratory depression.
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 Fentanyl
- Alvimopan + Fentanyl Contraindicated
- Fentanyl + Isocarboxazid Contraindicated
- Fentanyl + Olanzapine / samidorphan Contraindicated
- Fentanyl + Phenelzine Contraindicated
- Fentanyl + Tranylcypromine Contraindicated
- Alfentanil + Fentanyl 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 Fentanyl?
MediHelp rates the interaction as moderate. Efavirenz and Fentanyl 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 induce CYP3A4, the main enzyme that clears fentanyl, so fentanyl concentrations may fall and analgesia may be lost. In opioid-dependent patients this can trigger withdrawal symptoms. If efavirenz is later stopped, fentanyl levels can rise again and cause excess sedation or respiratory depression.
How serious is the interaction between Efavirenz and Fentanyl?
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 pain control and withdrawal signs after efavirenz is started and titrate the fentanyl dose to effect. When efavirenz is stopped, reduce the fentanyl dose and watch for sedation and respiratory depression.
What other medicines interact with Fentanyl?
MediHelp also lists interactions of Fentanyl with, for example, Alvimopan, Isocarboxazid, Olanzapine / samidorphan. The full list is on the Fentanyl page.
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