Metronidazole and Phenytoin Interaction
Drug interaction information between Metronidazole and Phenytoin.
Metronidazole and Phenytoin have a documented minor interaction in FDA labeling.
FDA drug labeling documents a minor-severity interaction between Metronidazole and Phenytoin. 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 makes your liver clear metronidazole out of your body too quickly, while metronidazole can cause phenytoin to build up to unsafe levels.
FDA Label Information
Drugs that Induce CYP450 Enzymes The simultaneous administration of drugs that induce microsomal liver enzymes, such as phenytoin or phenobarbital, may accelerate the elimination of metronidazole, resulting in reduced plasma levels; impaired clearance of phenytoin has also been reported.
Metronidazole Also Interacts With
- Theophylline major
- Lithium minor
- Disulfiram minor
- Cimetidine minor
- Phenobarbital minor
Phenytoin Also Interacts With
- Nirmatrelvir/Ritonavir major
- Posaconazole major
- Ranolazine major
- Voriconazole major
- Apixaban moderate
Frequently Asked Questions
What SPL severity band is on file for Metronidazole + Phenytoin?
Compiled FDA labeling labels this pair minor. 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 Metronidazole's 10. In the minor band specifically: Metronidazole has 9 (also Lithium, Disulfiram, Cimetidine, Phenobarbital); Phenytoin has 120 (also Atorvastatin, Omeprazole, Simvastatin, Methylphenidate).
What mechanism field is on file for Metronidazole and Phenytoin?
Phenytoin makes your liver clear metronidazole out of your body too quickly, while metronidazole can cause phenytoin to build up to unsafe levels.
Phenytoin carries more major-labeled pairs than Metronidazole
SPL source-record counts only. This page's band is minor · classes on file: Metronidazole (Nitroimidazole Antibiotic); Phenytoin (Anticonvulsant (Hydantoin)).
Phenytoin has 4 major-labeled pairs vs Metronidazole's 1. This page itself is in the minor band, not the major band.
1 major · 0 moderate · 9 minor · 10 total
- Other minor peers for Metronidazole
- Lithium
- Disulfiram
- Cimetidine
- Phenobarbital
4 major · 23 moderate · 120 minor · 147 total
- Other minor peers for Phenytoin
- Atorvastatin
- Omeprazole
- Simvastatin
- Methylphenidate
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.