What the FDA labels say about taking them together
Phenytoin and voriconazole
Phenytoin's FDA label of October 15, 2024 names voriconazole in its drug interactions section, and voriconazole's label names phenytoin too. The voriconazole label: “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.”
Check it at the source: the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.); the voriconazole FDA label on DailyMed (effective February 26, 2026, Roerig).
What does the phenytoin label say about voriconazole?
Phenytoin label, drug interactionsInteracting Agent: Azoles; Examples: Fluconazole, ketoconazole, itraconazole, miconazole, voriconazole
Source: FDA drug label (Phenytek), Mylan Pharmaceuticals Inc., effective October 15, 2024 (SPL set 0f94c791-8b07-4b41-927e-c9f28bec5f60), via openFDA; the full label on DailyMed
What does the voriconazole label say about phenytoin?
Voriconazole label, drug interactionsDrug/Drug Class (Mechanism of Interaction by the Drug): Phenytoin (CYP450 Induction); Voriconazole Plasma Exposure (C max and AUC τ after 200 mg every 12 hours): Significantly Reduced; Prevention or Management Recommendations: 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).
Voriconazole label (Xellia Pharmaceuticals USA LLC, January 11, 2023), drug interactionsDrug/Drug Class (Mechanism of Interaction by the Drug): Phenytoin (CYP450 Induction); Voriconazole Plasma Exposure (C max and AUC τ after 200 mg every 12 hours): Significantly Reduced; Recommendations for Voriconazole Dosage Adjustment/Comments: Increase voriconazole maintenance dose from 4 mg/kg to 5 mg/kg IV every12 hours
Source: FDA drug label (Voriconazole, NDA208562), Xellia Pharmaceuticals USA LLC, effective January 11, 2023 (SPL set 9ec6eda2-2f15-423b-9ec6-819379a426e1), via openFDA
Source: FDA drug label (VFEND), NDA021630 (Pf Prism Cv), as published by Roerig, effective February 26, 2026 (SPL set ce3ef5cf-3087-4d92-9d94-9eb8287228db), via openFDA; the full label on DailyMed
These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.
Both medicines on the record
| Phenytoin | Voriconazole | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Fungal infections |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.145 per capsule 100 mg capsule | $1.88 per tablet 200 mg tablet |
| Shortage now | No current entry | A presentation being discontinued |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once