Warfarin with Propylthiouracil Interaction Details
Brand Names Associated with Warfarin
- Coumadin®
- Jantoven®
- Warfarin
Brand Names Associated with Propylthiouracil
- Propycil
- Propylthiouracil
- PTU
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Nov 07, 2023
Interaction Effect
Decreased anticoagulant effectiveness
Interaction Summary
In hyperthyroid patients, the metabolism of vitamin K clotting factors is increased, resulting in increased sensitivity to oral anticoagulants. Antithyroid drugs, by reducing the extent of hyperthyroidism, decrease the metabolism of clotting factors and thus reduce the effects of oral anticoagulants . On the other hand, patients on anticoagulant therapy who are euthyroid due to antithyroid agents may develop marked hypoprothrombinemia if the antithyroid medications are ceased and they become thyrotoxic again . In one case report, treating patients with both methimazole and warfarin necessitates intensive and frequent monitoring, since alterations in thyroid function affect the response to anticoagulation .
Severity
Moderate
Onset
Delayed
Evidence
Probable
How To Manage Interaction
In patients receiving oral anticoagulant therapy, the prothrombin time ratio or international normalized ratio (INR) should be closely monitored with the addition and withdrawal of treatment with antithyroid drugs, and should be reassessed periodically during concurrent therapy. Increased anticoagulant doses may be required to maintain the desired level of anticoagulation.
Mechanism Of Interaction
Decreased metabolism of clotting factors
Literature Reports
A) One case report describes changes in thyroid hormone concentrations that significantly affected warfarin-induced anticoagulation in a patient with Graves' disease. A 54-year old man was treated with methimazole 30 mg/day for hyperthyroidism and enoxaparin then warfarin for atrial fibrillation. In the following 3 months after discharge, the patient's warfarin was repeatedly increased to 85 mg/week to achieve and maintain a therapeutic INR (range 2 - 3). The patient remained adequately anticoagulated for 12 weeks, when the methimazole dose was decreased to 10 mg/day. Continued hypothyroidism necessitated a stop of methimazole for 5 days, then resumed at a dose of 5 mg/day. This resulted in a supratherapeutic INR, and the warfarin was decreased to 60 mg/week. What followed was a pattern of methimazole dosage adjustments leading to significant changes in thyroid function, and subsequent changes in INR. After approximately 14 months of warfarin therapy, Two ECGs confirmed sustained normal sinus rhythm and anticoagulation was discontinued .
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.
Propylthiouracil Overview
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Propylthiouracil is used to treat hyperthyroidism (a condition that occurs when the thyroid gland produces too much thyroid hormone, speeding the body's metabolism, and causing certain symptoms) in adults and children 6 years of age or older. Propylthiouracil is in a class of medications called antithyroid agents. It works by stopping the thyroid gland from making thyroid hormone.
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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.