Warfarin with Dapsone Interaction Details

Brand Names Associated with Warfarin

Brand Names Associated with Dapsone

Medical Content Editor Dr. Brian Staiger, PharmD
Last updated Nov 07, 2023

Interaction Effect

Increased International Normalized Ratio (INR)

Interaction Summary

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 range. 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 .

Severity

Major

Onset

Delayed

Evidence

Probable

How To Manage Interaction

Concomitant use of dapsone and warfarin should be approached with caution as this may result in increased INR, which may increase the risk for bleeding. If concomitant use of dapsone and warfarin is required, more frequent monitoring of the patient's INR is recommended, especially during initiation and discontinuation of dapsone .

Mechanism Of Interaction

Competition for CYP2C9- and CYP3A4-mediated metabolism

Literature Reports

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 .

Warfarin Overview

• Warfarin is used to prevent blood clots from forming or growing larger in your blood and blood vessels. It is prescribed for people with certain types of irregular heartbeat, people with prosthetic (replacement or mechanical) heart valves, and people who have suffered a heart attack. Warfarin is also used to treat or prevent venous thrombosis (swelling and blood clot in a vein) and pulmonary embolism (a blood clot in the lung). Warfarin is in a class of medications called anticoagulants ('blood thinners'). It works by decreasing the clotting ability of the blood.

Dapsone Overview

• Dapsone is used to treat leprosy and skin infections.

• This medication is sometimes prescribed for other uses; ask your doctor or pharmacist for more information.

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Definitions

Severity Categories

Contraindicated

These drugs, generally, should not be used together simultaneously due to the high risk of severe adverse effects. Combining these medications can lead to dangerous health outcomes and should be strictly avoided unless otherwise instructed by your provider.

Major

This interaction could result in very serious and potentially life-threatening consequences. If you are taking this drug combination, it is very important to be under close medical supervision to minimize severe side effects and ensure your safety. It may be necessary to change a medication or dosage to prevent harm.

Moderate

This interaction has the potential to worsen your medical condition or alter the effectiveness of your treatment. It's important that you are monitored closely and you potentially may need to make adjustments in your treatment plan or drug dosage to maintain optimal health.

Minor

While this interaction is unlikely to cause significant problems, it could intensify side effects or reduce the effectiveness of one or both medications. Monitoring for changes in symptoms and your condition is recommended, and adjustments may be made if needed to manage any increased or more pronounced side effects.

Onset

Rapid: Onset of drug interaction typically occurs within 24 hours of co-administration.

Delayed: Onset of drug interaction typically occurs more than 24 hours after co-administration.

Evidence

Level of documentation of the interaction.

Established: The interaction is documented and substantiated in peer-reviewed medical literature.

Theoretical: This interaction is not fully supported by current medical evidence or well-documented sources, but it is based on known drug mechanisms, drug effects, and other relevant information.

How To Manage The Interaction

Provides a detailed discussion on how patients and clinicians can approach the identified drug interaction as well as offers guidance on what to expect and strategies to potentially mitigate the effects of the interaction. This may include recommendations on adjusting medication dosages, altering the timing of drug administration, or closely monitoring for specific symptoms.

It's important to note that all medical situations are unique, and management approaches should be tailored to individual circumstances. Patients should always consult their healthcare provider for personalized advice and guidance on managing drug interactions effectively.

Mechanism Of Interaction

The theorized or clinically determined reason (i.e., mechanism) why the drug-drug interaction occurs.

Disclaimer: The information provided on this page is for informational purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional regarding your specific circumstances and medical conditions.

Where Does Our Information Come From?

Information for our drug interactions is compiled from several drug compendia, including:

• Gold Standard Drug Database
• Micromedex
• Lexicomp
• DrugBank

The prescribing information for each drug, as published on DailyMED, is also used. 

Individual drug-drug interaction detail pages contain references specific to that interaction. You can click on the reference number within brackets '[]' to see what reference was utilized.

The information posted is fact-checked by HelloPharmacist clinicians and reviewed quarterly.