Warfarin with Levamisole Interaction Details
Brand Names Associated with Warfarin
- Coumadin®
- Jantoven®
- Warfarin
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Nov 07, 2023
Interaction Effect
An increased risk of bleeding
Interaction Summary
There have been case reports of prolongation of prothrombin time beyond the therapeutic range when levamisole and warfarin were used concurrently. Two separate cases of elderly patients receiving treatment for colon cancer reported pronounced increases in prothrombin time when levamisole and fluorouracil were administered along with warfarin . However, a causal relationship between levamisole and warfarin was not established .
Severity
Moderate
Onset
Delayed
Evidence
Probable
How To Manage Interaction
In patients receiving warfarin and levamisole concurrently, the prothrombin time ratio or international normalized ratio (INR) should be closely monitored. The warfarin dose may require adjustment to maintain the desired level of anticoagulation.
Mechanism Of Interaction
Decreased warfarin metabolism
Literature Reports
A) In a case reported , a 73-year-old man with prosthetic mitral and aortic valve replacement was stabilized on warfarin 22.5 mg weekly with a mean International Normalization Ratio (INR) of 2.43. After colon resection for colon cancer, he received maintenance doses of levamisole (50 mg three times daily for three days every other week) and fluorouracil (450 mg/m2/week). Within four weeks of beginning antineoplastic therapy, his INR increased from 3.04 to 39.56; thereafter, his warfarin was reduced to 7.5 mg weekly. With a decline in neutrophil count, he discontinued the levamisole-fluorouracil for five weeks. During this period, his INR dropped below therapeutic levels. When he was restarted on levamisole and fluorouracil, he again experienced a significant rise in prothrombin time.
B) A 60-year-old woman who had surgery for rectal carcinoma developed a deep vein thrombosis and pulmonary embolism for which she received heparin and warfarin therapy. The patient was then started on 5-flourouracil and levamisole for adjuvant rectal carcinoma treatment. When treatment started she was receiving warfarin 5 mg daily and had a prothrombin time between 13.6 and 19.7 seconds. After 10 days of levamisole and 5-flourouracil therapy, her prothrombin time increased to 22.6 seconds. After completing a 3-day course of levamisole eight days later, the patient complained of right flank pain which was accompanied by gross hematuria. The patient was then admitted to the hospital and had a prothrombin time greater than 40 seconds. Hematuria resolved after treatment with fresh frozen plasma and vitamin K .
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.