Drug interactions
Efavirenz + Phenobarbital
Severity: Major
Efavirenz and Phenobarbital: 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
Phenobarbital is a potent enzyme inducer and may lower efavirenz levels, risking virologic failure. Efavirenz may in turn alter phenobarbital exposure, and both cause CNS effects.
What this interaction means in plain words
Efavirenz and Phenobarbital 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
Induction of CYP2B6 and CYP3A4 by phenobarbital increases efavirenz clearance.
What to do
Monitor HIV viral load and efavirenz concentrations, and consider an alternative anticonvulsant or antiretroviral. Monitor phenobarbital levels and sedation.
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 Phenobarbital?
MediHelp rates the interaction as major. Efavirenz and Phenobarbital 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. Phenobarbital is a potent enzyme inducer and may lower efavirenz levels, risking virologic failure. Efavirenz may in turn alter phenobarbital exposure, and both cause CNS effects.
How serious is the interaction between Efavirenz and Phenobarbital?
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 HIV viral load and efavirenz concentrations, and consider an alternative anticonvulsant or antiretroviral. Monitor phenobarbital levels and sedation.
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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