Dapsone and Warfarin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Warfarin
Dapsone
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Increased International Normalized Ratio (INR)
Interaction Deep Dive
Both dapsone and warfarin are substrates of CYP2C9 and CYP3A4 and concomitant use may result in increased INR and an increased risk of bleeding due to competition of CYP2C9- and CYP3A4-mediated dapsone and warfarin metabolism. The CYP2C9 isoenzyme, in particular, is responsible for S-warfarin metabolism, the more potent enantiomer of warfarin. In one case study, coadministration of dapsone in a 41-year-old woman stable for 1 year on warfarin 22.5 mg/week resulted in a supratherapeutic INR which persisted until discontinuation of dapsone. A warfarin dose reduction of approximately 16% during concomitant use with dapsone failed to return the INR to within therapeutic range1. If an antibiotic, such as dapsone, is required in a patient taking warfarin, more frequent monitoring of INR is recommended, especially when the antibiotic is initiated and discontinued 2.
Why it happens (mechanism)
Competition for CYP2C9- and CYP3A4-mediated metabolism
Literature reports
1 report — tap to read
a) A supratherapeutic INR (3.9) was reported 5 days after the initiation of acyclovir, clindamycin, and dapsone for shingles and foot infection in a 41-year-old African American woman stable for 1 year on warfarin 22.5 mg/week. The dosages of 10 maintenance medications had not changed in the previous 5 months. In response to the elevated INR, the warfarin dose was reduced by approximately 16% that week and the original dose was resumed the following week. Despite the warfarin dose reduction, the supratherapeutic INR (4.3) persisted 2 weeks later, 5 days after the completion of the clindamycin and dapsone regimen. The warfarin dose was reduced by approximately 27% that week, and the original dose of 22.5 mg was resumed the following week. Two weeks later, the INR was within therapeutic range at 2.6 and has remained stable since 1.
Common questions
Can I take Dapsone and Warfarin together?
Increased International Normalized Ratio (INR) Always confirm with your pharmacist or prescriber before making any change.
How serious is the Dapsone and Warfarin interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Dapsone or Warfarin need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (2)
- Truong T & Haley J: Probable warfarin and dapsone interaction. Clin Appl Thromb Hemost 2012; 18(1):107-109. DOI
- Product Information: COUMADIN(R) oral tablets, intravenous injection powder lyophilized for solution, warfarin sodium oral tablets, intravenous injection powder lyophilized for solution. Bristol-Myers Squibb Company (per FDA), Princeton, NJ, 2011. DailyMed
Keep reading about Warfarin
Keep reading about Dapsone
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Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
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