Drug interactions
Doxycycline + Phenindione
Severity: Moderate
Doxycycline and Phenindione: 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
Tetracyclines may enhance the anticoagulant effect of vitamin K antagonists, raising INR and bleeding risk. The effect is reported mainly with warfarin and is extrapolated to phenindione.
What this interaction means in plain words
Doxycycline and Phenindione 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
Possibly reduced vitamin K-producing gut flora and altered clotting factor handling increases anticoagulant effect.
What to do
Monitor INR closely when doxycycline is started or stopped and reduce the phenindione dose if INR rises.
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?
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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 Phenindione?
MediHelp rates the interaction as moderate. Doxycycline and Phenindione 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. Tetracyclines may enhance the anticoagulant effect of vitamin K antagonists, raising INR and bleeding risk. The effect is reported mainly with warfarin and is extrapolated to phenindione.
How serious is the interaction between Doxycycline and Phenindione?
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 INR closely when doxycycline is started or stopped and reduce the phenindione dose if INR rises.
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.
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