Sulfamethoxazole and Warfarin: Drug Interaction Guide
Quick answer: This is a major interaction — avoid combining Sulfamethoxazole and Warfarin unless specifically directed by your doctor.
How Sulfamethoxazole interacts with Warfarin
Sulfamethoxazole inhibits CYP2C9 metabolism of S-warfarin and displaces it from albumin, significantly increasing INR and bleeding risk.
What you should do
Avoid where possible. If co-trimoxazole is essential, reduce warfarin dose by 25-50% and check INR within 3-5 days.
Key facts
Severity
Major — avoid combination
Mechanism
Sulfamethoxazole inhibits CYP2C9 metabolism of S-warfarin and displaces it from albumin, significantly increasing INR an...
Action
Avoid where possible. If co-trimoxazole is essential, reduce warfarin dose by 25-50% and check INR within 3-5 days.
Frequently asked questions
Can I take Sulfamethoxazole and Warfarin together?
No — this combination should generally be avoided. Avoid where possible. If co-trimoxazole is essential, reduce warfarin dose by 25-50% and check INR within 3-5 days.
What is the severity of this interaction?
The interaction between Sulfamethoxazole and Warfarin is classified as Major — avoid combination. Sulfamethoxazole inhibits CYP2C9 metabolism of S-warfarin and displaces it from albumin, significantly increasing INR and bleeding risk.
What should I do if I'm prescribed both?
Avoid where possible. If co-trimoxazole is essential, reduce warfarin dose by 25-50% and check INR within 3-5 days. Always consult your prescribing clinician — do not stop or change medications without medical guidance.
Last reviewed: by iMedic Medical Editorial Team. Our editorial process.