Drug interactions
Isoniazid + Warfarin
Severity: Moderate
Isoniazid and Warfarin: 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
Isoniazid can inhibit CYP enzymes involved in warfarin metabolism, and case reports describe increased INR and bleeding. Isoniazid-related liver injury can also alter coagulation.
What this interaction means in plain words
Isoniazid and Warfarin 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.
Isoniazid belongs to Anti Bacterial; Warfarin belongs to Cardiovascular.
Why it happens
Inhibition of CYP2C19, CYP3A4 and other enzymes metabolising the warfarin R-enantiomer, possibly with hepatic effects on clotting factors.
What to do
Check INR more frequently when isoniazid is started or stopped and adjust warfarin dose accordingly.
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 Isoniazid
Other interactions of Warfarin
- Defibrotide + Warfarin Contraindicated
- Ketorolac + Warfarin Contraindicated
- Abciximab + Warfarin Major
- Acetylsalicylic acid + Warfarin Major
- Adagrasib + Warfarin Major
- Amiodarone + Warfarin Major
Frequently asked questions
Can I take Isoniazid with Warfarin?
MediHelp rates the interaction as moderate. Isoniazid and Warfarin 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. Isoniazid can inhibit CYP enzymes involved in warfarin metabolism, and case reports describe increased INR and bleeding. Isoniazid-related liver injury can also alter coagulation.
How serious is the interaction between Isoniazid and Warfarin?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Check INR more frequently when isoniazid is started or stopped and adjust warfarin dose accordingly.
What other medicines interact with Isoniazid?
MediHelp also lists interactions of Isoniazid with, for example, Bacillus calmette-guerin substrain tice, Benzhydrocodone / acetaminophen, Carbamazepine. The full list is on the Isoniazid page.
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