Drug interactions
Itraconazole + Phenobarbital
Severity: Major
Itraconazole and Phenobarbital: major interaction.
Last updated Sources: US FDA label
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 inducer of metabolic enzymes and transporters and can markedly lower itraconazole concentrations. This may lead to subtherapeutic antifungal exposure and treatment failure.
What this interaction means in plain words
Itraconazole 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
Phenobarbital induces CYP3A4 and P-glycoprotein, increasing itraconazole clearance and reducing bioavailability.
What to do
Avoid the combination where possible, since itraconazole labeling advises against use with potent inducers. If unavoidable, monitor itraconazole serum levels and clinical response, and consider a non-interacting antifungal or anticonvulsant.
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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References
Other interactions of Itraconazole
- Alfuzosin + Itraconazole Contraindicated
- Alprazolam + Itraconazole Contraindicated
- Avanafil + Itraconazole Contraindicated
- Conivaptan + Itraconazole Contraindicated
- Dihydroergotamine intranasal + Itraconazole Contraindicated
- Dihydroergotamine + Itraconazole Contraindicated
Frequently asked questions
Can I take Itraconazole with Phenobarbital?
MediHelp rates the interaction as major. Itraconazole 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 inducer of metabolic enzymes and transporters and can markedly lower itraconazole concentrations. This may lead to subtherapeutic antifungal exposure and treatment failure.
How serious is the interaction between Itraconazole 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: Avoid the combination where possible, since itraconazole labeling advises against use with potent inducers. If unavoidable, monitor itraconazole serum levels and clinical response, and consider a non-interacting antifungal or anticonvulsant.
What other medicines interact with Itraconazole?
MediHelp also lists interactions of Itraconazole with, for example, Alfuzosin, Alprazolam, Avanafil. The full list is on the Itraconazole page.
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