Phenytoin and Voriconazole Interaction
Drug interaction information between Phenytoin and Voriconazole.
Phenytoin and Voriconazole have a documented major interaction in FDA labeling.
FDA drug labeling documents a major-severity interaction between Phenytoin and Voriconazole. This page displays the available source-record category and label text. The category is not an individual risk estimate or medication-combination direction.
How They Interact
Phenytoin speeds up how fast the body gets rid of voriconazole, while voriconazole slows down the breakdown of phenytoin. This means the antifungal may not work well, and the seizure medicine could reach toxic levels.
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). Phenytoin (CYP2C9 Inhibition)...
Phenytoin Also Interacts With
- Nirmatrelvir/Ritonavir major
- Posaconazole major
- Ranolazine major
- Apixaban moderate
- Aprepitant moderate
Voriconazole Also Interacts With
- Norethindrone major
- Rifampin major
- Lurasidone major
- Pimozide major
- Ivabradine major
Frequently Asked Questions
What SPL severity band is on file for Phenytoin + Voriconazole?
Compiled FDA labeling labels this pair major. That is a source-record field, not an individual medication-combination decision.
Which drug in this pair has the larger labeled-interaction portfolio?
Phenytoin has 147 labeled pairs on file vs Voriconazole's 50. In the major band specifically: Phenytoin has 4 (also Nirmatrelvir/Ritonavir, Posaconazole, Ranolazine); Voriconazole has 8 (also Norethindrone, Rifampin, Lurasidone, Pimozide).
What mechanism field is on file for Phenytoin and Voriconazole?
Phenytoin speeds up how fast the body gets rid of voriconazole, while voriconazole slows down the breakdown of phenytoin. This means the antifungal may not work well, and the seizure medicine could reach toxic levels.
Voriconazole carries more major-labeled pairs than Phenytoin
SPL source-record counts only. This page's band is major · classes on file: Phenytoin (Anticonvulsant (Hydantoin)); Voriconazole (Azole Antifungal).
Voriconazole has 8 major-labeled pairs vs Phenytoin's 4.
4 major · 23 moderate · 120 minor · 147 total
- Other major peers for Phenytoin
- Nirmatrelvir/Ritonavir
- Posaconazole
- Ranolazine
8 major · 9 moderate · 33 minor · 50 total
- Other major peers for Voriconazole
- Norethindrone
- Rifampin
- Lurasidone
- Pimozide
Sources: FDA Drug Labels (SPL) via openFDA (2026). This is for informational purposes only and is not medical advice. This registry does not provide individual medication-combination directions.
Read our methodology - how this data is sourced, computed, and verified.