Phenobarbital and Voriconazole Interaction
Drug interaction information between Phenobarbital and Voriconazole.
Phenobarbital and Voriconazole have a documented major interaction in FDA labeling.
FDA drug labeling documents a major-severity interaction between Phenobarbital and Voriconazole. Major interactions are generally avoided, moderate ones may need monitoring or a dose adjustment, and minor ones are usually low-risk. This page shows the documented mechanism and guidance. Label-documented interactions are not a complete safety review, so always confirm your own medications with a pharmacist or doctor. Educational information, not medical advice.
How They Interact
Phenobarbital causes the body to process voriconazole much faster than normal, which significantly lowers the amount of medicine in your system. This makes the treatment much less likely to fight off an infection.
What To Do
This combination is contraindicated and should be avoided. Talk to your doctor about using a different medication that does not interfere with your treatment.
FDA Label Information
Carbamazepine (CYP450 Induction) Not Studied In Vivo or In Vitro , but Likely to Result in Significant Reduction Contraindicated Long Acting Barbiturates (e.g., phenobarbital, mephobarbital) (CYP450 Induction) Not Studied In Vivo or In Vitro , but Likely to Result in Significant Reduction Contraindicated Phenytoin (CYP450 Induction) Significantly Reduced Increase voriconazole maintenance dose from 4 mg/kg to 5 mg/kg IV every 12 hours or from 200 mg to 400 mg orally every 12 hours (100 mg to 200 mg orally every 12 hours in patients weighing less than 40 kg).
Phenobarbital Also Interacts With
- Nirmatrelvir/Ritonavir major
- Ranolazine major
- Canagliflozin moderate
- Cenobamate moderate
- Clarithromycin moderate
Voriconazole Also Interacts With
- Norethindrone major
- Rifampin major
- Lurasidone major
- Pimozide major
- Ivabradine major
Frequently Asked Questions
Can I take Phenobarbital and Voriconazole together?
This is a major interaction. This combination is contraindicated and should be avoided. Talk to your doctor about using a different medication that does not interfere with your treatment.
How serious is the interaction between Phenobarbital and Voriconazole?
This interaction is classified as "major" severity by the FDA. Major interactions may be life-threatening or cause serious side effects.
Why do Phenobarbital and Voriconazole interact?
Phenobarbital causes the body to process voriconazole much faster than normal, which significantly lowers the amount of medicine in your system. This makes the treatment much less likely to fight off an infection.
Understanding the Phenobarbital and Voriconazole Interaction
FDA-approved prescribing information for these two drugs flags their combination as a major-severity interaction. Phenobarbital belongs to the Anticonvulsant (Barbiturate) class and Voriconazole belongs to the Azole Antifungal class - two categories that can collide when co-prescribed. The mechanism described in FDA labeling is: Phenobarbital causes the body to process voriconazole much faster than normal, which significantly lowers the amount of medicine in your system. Severity tiers matter: major flags generally advise avoidance, moderate flags often require monitoring or dose adjustment, and minor flags may only call for awareness.
Context around a specific patient determines real-world impact. Phenobarbital has 59 total documented interactions on file in this dataset, and Voriconazole has 50. Each additional medication compounds the interaction surface, which is why pharmacists run full-profile checks rather than evaluating one pair at a time. FDA-derived guidance for this pair is: This combination is contraindicated and should be avoided. Timing of doses, renal and hepatic function, age, and other concurrent prescriptions all shape whether a labeled interaction matters clinically.
An interaction flag is not a verdict. A large share of labeled interactions are managed routinely in clinical practice, the fix may be as simple as spacing doses or adding a monitoring test. Others require the prescriber to choose a different medication entirely. This page surfaces FDA-sourced labeling and openFDA data for educational purposes only; it is not medical advice and cannot account for your full clinical picture. Never start, stop, or adjust either Phenobarbital or Voriconazole based on a web page, speak with your prescriber or pharmacist before making any change.
Sources: FDA Drug Labels (SPL) via openFDA (2026). This is for informational purposes only and is not medical advice. Always consult your healthcare provider about drug interactions.
Read our methodology - how this data is sourced, computed, and verified.