Warfarin with Rifaximin Interaction Details
Brand Names Associated with Warfarin
- Coumadin®
- Jantoven®
- Warfarin
Brand Names Associated with Rifaximin
- Rifaximin
- Xifaxan®
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Nov 08, 2023
Interaction Effect
Decreased anticoagulant efficacy of warfarin
Interaction Summary
Use caution if warfarin is coadministered with rifaximin in patients with small intestine bacterial overgrowth, due to possible enzyme induction, which may lead to increased warfarin metabolism and decreased INR. In 1 case report, a 49-year-old female with a history of pulmonary embolism and antiphospholipid syndrome failed to achieve adequate anticoagulation on warfarin while receiving concurrent rifaximin therapy for small intestine bacterial overgrowth. Despite a 33% weekly warfarin dosage increase from baseline, the patient's INR remained subtherapeutic at 1.4 during rifaximin treatment. Rechallenge with a second course of rifaximin led to similar results. When adding or withdrawing rifaximin therapy in a patient with small intestine bacterial overgrowth and on warfarin, monitor prothrombin time (PT) and INR frequently. Higher doses of warfarin may be needed to maintain adequate anticoagulation.
Severity
Moderate
Onset
Delayed
Evidence
Theoretical
How To Manage Interaction
Use caution if warfarin is coadministered with rifaximin in patients with small intestine bacterial overgrowth, due to possible enzyme induction, which may lead to increased warfarin metabolism and decreased INR. When adding or withdrawing rifaximin therapy in a patient on warfarin, monitor prothrombin time (PT) and INR frequently. When used with rifaximin, higher doses of warfarin may be needed to maintain adequate anticoagulation.
Mechanism Of Interaction
Unknown
Literature Reports
A) A 49-year-old female with a history of pulmonary embolism and antiphospholipid syndrome failed to achieve adequate anticoagulation on warfarin while receiving concurrent rifaximin therapy for small intestine bacterial overgrowth (SIBO). The only relevant medical history was chronic malnutrition requiring percutaneous endoscopic gastrostomy placement for nutritional supplementation (Ensure 6 to 7 cans nightly; 20 mcg of vitamin K/can). The patient had been maintained on adequate anticoagulation for 5 months previously with warfarin 7.5 mg/day (INR range of 2 to 3.5). Following diagnosis of SIBO, the patient received treatment with rifaximin 400 mg orally 3 times daily for 10 days followed by 400 mg twice daily for 25 days. Five days following concomitant warfarin and rifaximin treatment, the INR was subtherapeutic at 1.2; other contributing factors for the decrease in INR were ruled out and vitamin K intake remained stable. Two weeks later, despite a weekly warfarin dosage increase by 13%, the INR remained subtherapeutic at 1.2; at 4 weeks, the INR was 1.4 with a 33% weekly warfarin dosage increase from baseline. Twelve days after rifaximin therapy completion, the INR became supratherapeutic at 4.2, requiring warfarin dose titration to achieve a therapeutic INR. At 26 days following rifaximin discontinuation, the INR was therapeutic (2.3) at a warfarin dose of 7.5 mg/day; however, it was still lower than the patient's usual INR on this warfarin regimen. After another course of rifaximin, similar results of subtherapeutic INRs were reported .
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.
Rifaximin Overview
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Rifaximin 200-mg tablets are used to treat traveler's diarrhea caused by certain bacteria in adults and children at least 12 years of age. Rifaximin 550-mg tablets are used to prevent episodes of hepatic encephalopathy (changes in thinking, behavior, and personality caused by a build-up of toxins in the brain in people who have liver disease) in adults who have liver disease and to treat irritable bowel syndrome (with diarrhea) in adults. Rifaximin is in a class of medications called antibiotics. Rifaximin treats traveler's diarrhea and irritable bowel syndrome by stopping the growth of the bacteria that cause diarrhea. Rifaximin treats hepatic encephalopathy by stopping the growth of bacteria that produce toxins and that may worsen liver disease. Rifaximin will not work to treat traveler's diarrhea that is bloody or occurs with fever.
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Antibiotics such as rifaximin will not work for colds, flu, or other viral infections. Taking antibiotics when they are not needed increases your risk of getting an infection later that resists antibiotic treatment.
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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.