Phenytoin and Aprepitant Interaction
Drug interaction information between Phenytoin and Aprepitant.
Phenytoin and Aprepitant have a documented moderate interaction in FDA labeling.
FDA drug labeling documents a moderate-severity interaction between Phenytoin and Aprepitant. 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 can speed up how your body processes aprepitant, which may make the aprepitant not work as well.
FDA Label Information
Intervention Avoid concomitant use of aprepitant Examples rifampin, carbamazepine, phenytoin 7.1 Effect of Aprepitant on the Pharmacokinetics of Other Drugs Aprepitant is a substrate, a weak-to-moderate (dose-dependent) inhibitor, and an inducer of CYP3A4. Intervention Avoid concomitant use of aprepitant Examples rifampin, carbamazepine, phenytoin
Phenytoin Also Interacts With
- Nirmatrelvir/Ritonavir major
- Posaconazole major
- Ranolazine major
- Voriconazole major
- Apixaban moderate
Aprepitant Also Interacts With
- Pimozide major
- Alprazolam moderate
- Diltiazem moderate
- Methylprednisolone moderate
- Ketoconazole moderate
Frequently Asked Questions
What SPL severity band is on file for Phenytoin + Aprepitant?
Compiled FDA labeling labels this pair moderate. 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 Aprepitant's 22. In the moderate band specifically: Phenytoin has 23 (also Apixaban, Canagliflozin, Carbidopa/Levodopa, Clarithromycin); Aprepitant has 9 (also Alprazolam, Diltiazem, Methylprednisolone, Ketoconazole).
What mechanism field is on file for Phenytoin and Aprepitant?
Phenytoin can speed up how your body processes aprepitant, which may make the aprepitant not work as well.
Phenytoin carries more major-labeled pairs than Aprepitant
SPL source-record counts only. This page's band is moderate · classes on file: Phenytoin (Anticonvulsant (Hydantoin)); Aprepitant (NK1 Receptor Antagonist (Antiemetic)).
Phenytoin has 4 major-labeled pairs vs Aprepitant's 1. This page itself is in the moderate band, not the major band.
4 major · 23 moderate · 120 minor · 147 total
- Other moderate peers for Phenytoin
- Apixaban
- Canagliflozin
- Carbidopa/Levodopa
- Clarithromycin
1 major · 9 moderate · 12 minor · 22 total
- Other moderate peers for Aprepitant
- Alprazolam
- Diltiazem
- Methylprednisolone
- Ketoconazole
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.