Phenobarbital and Doxycycline Interaction
Drug interaction information between Phenobarbital and Doxycycline.
Phenobarbital and Doxycycline have a documented minor interaction in FDA labeling.
FDA drug labeling documents a minor-severity interaction between Phenobarbital and Doxycycline. 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
Phenobarbital causes your body to get rid of the antibiotic doxycycline more quickly, which could make it less effective at fighting infections.
FDA Label Information
Doxycycline Phenobarbital has been shown to shorten the half-life of doxycycline for as long as 2 weeks after barbiturate therapy is discontinued. If phenobarbital and doxycycline are administered concurrently, the clinical response to doxycycline should be monitored closely.
Phenobarbital Also Interacts With
- Nirmatrelvir/Ritonavir major
- Ranolazine major
- Voriconazole major
- Canagliflozin moderate
- Cenobamate moderate
Doxycycline Also Interacts With
- Tetracycline moderate
- Rifampin moderate
- Carbamazepine minor
- Bismuth Subsalicylate minor
- Phenytoin minor
Frequently Asked Questions
What SPL severity band is on file for Phenobarbital + Doxycycline?
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?
Phenobarbital has 59 labeled pairs on file vs Doxycycline's 9. In the minor band specifically: Phenobarbital has 43 (also Estradiol, Progesterone, Griseofulvin, Bazedoxifene); Doxycycline has 7 (also Carbamazepine, Bismuth Subsalicylate, Phenytoin, Doxycycline Hyclate).
What mechanism field is on file for Phenobarbital and Doxycycline?
Phenobarbital causes your body to get rid of the antibiotic doxycycline more quickly, which could make it less effective at fighting infections.
Phenobarbital carries more major-labeled pairs than Doxycycline
SPL source-record counts only. This page's band is minor · classes on file: Phenobarbital (Anticonvulsant (Barbiturate)); Doxycycline (Tetracycline Antibiotic).
Phenobarbital has 3 major-labeled pairs vs Doxycycline's 0. This page itself is in the minor band, not the major band.
3 major · 13 moderate · 43 minor · 59 total
- Other minor peers for Phenobarbital
- Estradiol
- Progesterone
- Griseofulvin
- Bazedoxifene
0 major · 2 moderate · 7 minor · 9 total
- Other minor peers for Doxycycline
- Carbamazepine
- Bismuth Subsalicylate
- Phenytoin
- Doxycycline Hyclate
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.