Phenytoin and Posaconazole Interaction
Drug interaction information between Phenytoin and Posaconazole.
Phenytoin and Posaconazole have a documented major interaction in FDA labeling.
FDA drug labeling documents a major-severity interaction between Phenytoin and Posaconazole. 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 causes the body to break down posaconazole much faster than usual, which can make the antifungal medicine less effective.
FDA Label Information
Interaction Drug Interaction Rifabutin, phenytoin, efavirenz, cimetidine, esomeprazole* Avoid coadministration unless the benefit outweighs the risks ( 7.6 , 7.7 , 7.8 , 7.9 ) Other drugs metabolized by CYP3A4 Consider dosage adjustment and monitor for adverse effects and toxicity ( 7.1 , 7.10 , 7.11 ) Digoxin Monitor digoxin plasma concentrations ( 7.12 ) Fosamprenavir, metoclopramide* Monitor for breakthrough fungal infections ( 7.6 , 7.13 ) *The drug interactions with esomeprazole and metoclopramide do not apply to posaconazole tablets. 7.8 Phenytoin Phenytoin induces UDP-glucuronidase...
Phenytoin Also Interacts With
- Nirmatrelvir/Ritonavir major
- Ranolazine major
- Voriconazole major
- Apixaban moderate
- Aprepitant moderate
Posaconazole Also Interacts With
- Esomeprazole major
- Digoxin major
- Cimetidine major
- Metoclopramide major
- Efavirenz/Emtricitabine/Tenofovir moderate
Frequently Asked Questions
What SPL severity band is on file for Phenytoin + Posaconazole?
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 Posaconazole's 27. In the major band specifically: Phenytoin has 4 (also Nirmatrelvir/Ritonavir, Ranolazine, Voriconazole); Posaconazole has 5 (also Esomeprazole, Digoxin, Cimetidine, Metoclopramide).
What mechanism field is on file for Phenytoin and Posaconazole?
Phenytoin causes the body to break down posaconazole much faster than usual, which can make the antifungal medicine less effective.
Posaconazole carries more major-labeled pairs than Phenytoin
SPL source-record counts only. This page's band is major · classes on file: Phenytoin (Anticonvulsant (Hydantoin)); Posaconazole (Azole Antifungal).
Posaconazole has 5 major-labeled pairs vs Phenytoin's 4.
4 major · 23 moderate · 120 minor · 147 total
- Other major peers for Phenytoin
- Nirmatrelvir/Ritonavir
- Ranolazine
- Voriconazole
5 major · 5 moderate · 17 minor · 27 total
- Other major peers for Posaconazole
- Esomeprazole
- Digoxin
- Cimetidine
- Metoclopramide
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.