Drug interactions
Efavirenz + Fentanyl transdermal
Severity: Major
Efavirenz and Fentanyl transdermal: 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
Efavirenz can lower fentanyl plasma concentrations, causing reduced pain control or opioid withdrawal in dependent patients. If efavirenz is stopped, fentanyl levels may rise and cause delayed respiratory depression and excess sedation.
What this interaction means in plain words
Efavirenz and Fentanyl transdermal 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.
Why it happens
Efavirenz induces CYP3A4, increasing the metabolism of fentanyl.
What to do
Monitor analgesic response and withdrawal signs and adjust the fentanyl dose as needed. After stopping efavirenz, monitor closely for sedation and respiratory depression and consider reducing the fentanyl dose.
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
Frequently asked questions
Can I take Efavirenz with Fentanyl transdermal?
MediHelp rates the interaction as major. Efavirenz and Fentanyl transdermal 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 can lower fentanyl plasma concentrations, causing reduced pain control or opioid withdrawal in dependent patients. If efavirenz is stopped, fentanyl levels may rise and cause delayed respiratory depression and excess sedation.
How serious is the interaction between Efavirenz and Fentanyl transdermal?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor analgesic response and withdrawal signs and adjust the fentanyl dose as needed. After stopping efavirenz, monitor closely for sedation and respiratory depression and consider reducing the fentanyl dose.
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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