Drug interactions
Doxycycline + Phenobarbital
Severity: Moderate
Doxycycline and Phenobarbital: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Phenobarbital is a potent enzyme inducer and shortens doxycycline half-life, reducing antibiotic exposure. Therapeutic failure of doxycycline is possible, especially in longer courses.
What this interaction means in plain words
Doxycycline and Phenobarbital can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Why it happens
Phenobarbital induction of hepatic enzymes increases doxycycline clearance.
What to do
Monitor for lack of clinical response and consider increasing the doxycycline dose or choosing a different antibiotic for serious infections. Readjust when phenobarbital is discontinued.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Doxycycline and Phenobarbital, the additional notes, the evidence detail and the whole-prescription interaction checker.
- Full clinical management advice
- Additional notes
- Evidence detail
- Interaction checker for a whole prescription
Try Pro+ free for 7 days on the web. No card needed.
Other interactions of Doxycycline
- Acitretin + Doxycycline Contraindicated
- Aminolevulinic acid + Doxycycline Major
- Cholera vaccine + Doxycycline Major
- Doxycycline + Isotretinoin Major
- Doxycycline + Methoxyflurane Major
- Doxycycline + Microbiota Major
Frequently asked questions
Can I take Doxycycline with Phenobarbital?
MediHelp rates the interaction as moderate. Doxycycline and Phenobarbital can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Phenobarbital is a potent enzyme inducer and shortens doxycycline half-life, reducing antibiotic exposure. Therapeutic failure of doxycycline is possible, especially in longer courses.
How serious is the interaction between Doxycycline and Phenobarbital?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor for lack of clinical response and consider increasing the doxycycline dose or choosing a different antibiotic for serious infections. Readjust when phenobarbital is discontinued.
What other medicines interact with Doxycycline?
MediHelp also lists interactions of Doxycycline with, for example, Acitretin, Aminolevulinic acid, Cholera vaccine. The full list is on the Doxycycline page.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.
