Terbinafine with Warfarin Interaction Details
Brand Names Associated with Terbinafine
- Lamisil®
- Terbinafine
Brand Names Associated with Warfarin
- Coumadin®
- Jantoven®
- Warfarin
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Jan 04, 2024
Interaction Effect
An alteration of warfarin efficacy
Interaction Summary
The clearance of warfarin or the effect of warfarin on prothrombin time has been reported to not be influenced by the presence of terbinafine. However, one case report described an elderly female who experienced a gastrointestinal bleed following one month of comedication with terbinafine and warfarin . Another case report describes a female who required increases in her warfarin dose when terbinafine was coadministered .
Severity
Moderate
Onset
Delayed
Evidence
Probable
How To Manage Interaction
Patients prescribed terbinafine and warfarin should be monitored for signs of excessive bleeding and also for signs of decreased warfarin efficacy. Prothrombin times and international normalized ratios (INRs) should also be closely followed, and the dose of warfarin should be adjusted as necessary.
Mechanism Of Interaction
Unknown
Literature Reports
A) In a randomized, double-blind, placebo-controlled, crossover study, no clinically significant pharmacokinetic or pharmacodynamic interactions were observed when racemic warfarin (a single 30 mg oral dose) was administered concomitantly with terbinafine (250 mg daily for 14 days) to 16 healthy males .
B) A 71-year-old female stabilized on warfarin 5 mg daily for deep-vein thrombosis had a prothrombin time (PT) of 21.5 seconds and an international normalized ratio (INR) of 3.1. Other medications included cimetidine 400 mg twice daily, hydrochlorothiazide 25 mg daily, triamterene 12.5 mg daily, thyroxine 0.25 mg daily, and imipramine 25 mg daily, all of which she had been taking for at least the previous two years. Terbinafine 250 mg daily was prescribed for onychomycosis, and 32 days later she presented with gastrointestinal bleeding. Her PT was 125 seconds and the INR was 11 on admission. Cimetidine is known to decrease the clearance of terbinafine by 33%, resulting in higher than expected terbinafine plasma concentrations. This patient may have experienced an interaction with warfarin at the higher concentration of terbinafine which may not manifest itself at lower concentrations of terbinafine .
C) A 68-year-old female was receiving warfarin for 22 years and had a stable INR between 2 and 3. She was prescribed oral terbinafine 250 mg daily for three months to treat tinea unguium. A month following terbinafine initiation, her international normalized ratio (INR) decreased to 1.1. Her warfarin dose was increased from 5.5 mg daily to 8 mg daily over a period of three weeks to keep the INR between 2 and 3. Terbinafine was discontinued at week 12, and her warfarin dose was slowly decreased over a period of four weeks back to 5.5 mg daily, where she remained stabilized .
Terbinafine Overview
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Terbinafine granules are used to treat fungal infections of the scalp. Terbinafine tablets are used to treat fungal infections of the toenails and fingernails. Terbinafine is in a class of medications called antifungals. It works by stopping the growth of fungi.
Warfarin Overview
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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.
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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:
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.