Allopurinol with Phenprocoumon Interaction Details
Brand Names Associated with Allopurinol
- Allopurinol
- Lopurin®
- Zyloprim®
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Feb 27, 2024
Interaction Effect
Increased INR
Interaction Summary
Exposure to warfarin (or another coumarin-derivative anticoagulant) might be increased, resulting in an increased INR, when coadministered with allopurinol, a CYP1A2 inhibitor. Consider the inhibition potential when initiating, adjusting, or discontinuing concomitant use and monitor INR closely[1].
Severity
Major
Onset
Delayed
Evidence
Probable
How To Manage Interaction
Exposure to warfarin (or another coumarin-derivative anticoagulant) might be increased, resulting in an increased INR, when coadministered with allopurinol, a CYP1A2 inhibitor. Consider the inhibition potential when initiating, adjusting, or discontinuing concomitant use and monitor INR closely[1].
Mechanism Of Interaction
Inhibition of CYP1A2-mediated anticoagulant metabolism by allopurinol
Literature Reports
A) Concomitant allopurinol and warfarin therapy has been reported to result in enhancement of warfarin activity as measured by prolongation of prothrombin time [2][3][4].
B) Allopurinol may increase the hypoprothrombinemic effect of oral anticoagulants in some patients [5][6][7].
C) An 83-year-old female received 300 mg daily of allopurinol for 12 days and developed a prolonged prothrombin time to a maximum value of 48.8 seconds three days after the patient had discontinued indomethacin but while she continued to receive warfarin and allopurinol [8].
References
1 ) Product Information: COUMADIN(R) oral tablets, warfarin sodium oral tablets. Bristol-Myers Squibb Company (per FDA), Princeton, NJ, 2017.
2 ) Avery GS: Check-list of potential clinically important interactions. Drugs 1973; 5:187-211.
3 ) Koch-Weser J & Koch-Weser J: Drug interactions in cardiovascular therapy. Am Heart J 1975; 90:93-116.
4 ) Koch-Weser J & Sellers EM: Drug interactions with coumarin anticoagulants (part 1). N Engl J Med 1971a; 285:487-498.
5 ) Vesell ES, Passananti GT, & Greene FE: Impairment of drug metabolism in man by allopurinol and nortriptyline. N Engl J Med 1970; 283:1484-1488.
6 ) Pond SM, Graham GG, Wade DN, et al: The effects of allopurinol and clofibrate on the elimination of coumarin anticoagulants in man. Aust N Z J Med 1975; 5:324-328.
7 ) Jahnchen E, Meinertz I, & Gilfrich HJ: Interaction of allopurinol with phenprocoumon in man. Klin Wochensch 1977; 55:759-761.
8 ) Self TH, Evans WE, & Ferguson T: Drug enhancement of warfarin activity (letter). Lancet 1975; 2:557-558.
Allopurinol Overview
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Allopurinol is used to treat gout (a type of arthritis in which uric acid, a naturally occurring substance in the body, builds up in the joints and causes sudden attacks of redness, swelling, pain, and heat in one or more joints). Allopurinol is also used to treat high levels of uric acid that builds up in the blood as tumors break down in people with certain types of cancer who are being treated with chemotherapy medications. It is also used to treat kidney stones that have come back in people who have high levels of uric acid in their urine. Allopurinol is in a class of medications called xanthine oxidase inhibitors. It works by reducing the production of uric acid in the body. High levels of uric acid may cause gout attacks or kidney stones. Allopurinol is used to prevent gout attacks, not to treat them once they occur.
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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.