Doxycycline and Phenytoin Interaction
Drug interaction information between Doxycycline and Phenytoin.
Doxycycline and Phenytoin have a documented minor interaction in FDA labeling.
FDA drug labeling documents a minor-severity interaction between Doxycycline 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 speeds up how quickly your body breaks down and removes doxycycline from your system.
FDA Label Information
Barbiturates, carbamazepine, and phenytoin decrease the half-life of doxycycline.
Doxycycline Also Interacts With
- Tetracycline moderate
- Rifampin moderate
- Carbamazepine minor
- Bismuth Subsalicylate minor
- Doxycycline Hyclate 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 Doxycycline + 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 Doxycycline's 9. In the minor band specifically: Doxycycline has 7 (also Carbamazepine, Bismuth Subsalicylate, Doxycycline Hyclate, Ethinyl Estradiol); Phenytoin has 120 (also Atorvastatin, Omeprazole, Simvastatin, Methylphenidate).
What mechanism field is on file for Doxycycline and Phenytoin?
Phenytoin speeds up how quickly your body breaks down and removes doxycycline from your system.
Phenytoin carries more major-labeled pairs than Doxycycline
SPL source-record counts only. This page's band is minor · classes on file: Doxycycline (Tetracycline Antibiotic); Phenytoin (Anticonvulsant (Hydantoin)).
Phenytoin has 4 major-labeled pairs vs Doxycycline's 0. This page itself is in the minor band, not the major band.
0 major · 2 moderate · 7 minor · 9 total
- Other minor peers for Doxycycline
- Carbamazepine
- Bismuth Subsalicylate
- Doxycycline Hyclate
- Ethinyl Estradiol
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.