Drug interactions
Sulfadiazine + Warfarin
Severity: Major
Sulfadiazine and Warfarin: major 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
Sulfadiazine can raise warfarin exposure and strengthen its anticoagulant effect, increasing the INR and the risk of serious bleeding. The effect usually appears within days of starting the sulfonamide.
What this interaction means in plain words
Sulfadiazine and Warfarin can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Why it happens
Sulfonamides inhibit CYP2C9-mediated metabolism of S-warfarin and may displace warfarin from plasma protein binding.
What to do
Check INR within a few days of starting or stopping sulfadiazine and reduce the warfarin dose as indicated by results. Consider an alternative antibacterial if feasible.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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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 Sulfadiazine with Warfarin?
MediHelp rates the interaction as major. Sulfadiazine and Warfarin can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Sulfadiazine can raise warfarin exposure and strengthen its anticoagulant effect, increasing the INR and the risk of serious bleeding. The effect usually appears within days of starting the sulfonamide.
How serious is the interaction between Sulfadiazine and Warfarin?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Check INR within a few days of starting or stopping sulfadiazine and reduce the warfarin dose as indicated by results. Consider an alternative antibacterial if feasible.
What other medicines interact with Warfarin?
MediHelp also lists interactions of Warfarin with, for example, Defibrotide, Ketorolac, Abciximab. The full list is on the Warfarin page.
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