Warfarin with Atovaquone Interaction Details
Brand Names Associated with Warfarin
- Coumadin®
- Jantoven®
- Warfarin
Brand Names Associated with Atovaquone
- Atovaquone
- Mepron®
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Nov 07, 2023
Interaction Effect
Increased INR
Interaction Summary
An increased INR was reported in a patient coadministered atovaquone and warfarin. The possible mechanism of interaction is protein binding displacement of warfarin by atovaquone. Exercise caution when co-administering atovaquone and warfarin due to the potential for increased INR.
Severity
Moderate
Onset
Unspecified
Evidence
Probable
How To Manage Interaction
Exercise caution when co-administering atovaquone and warfarin due to the potential for increased INR.
Mechanism Of Interaction
Protein displacement of warfarin by atovaquone
Literature Reports
A) The INR of a 53-year-old African American man on warfarin increased within 7 days of starting atovaquone. The patient started a 12-month course of warfarin 5 mg/day for pulmonary emboli and DVT, 1 month of which included concomitant atovaquone therapy; however, atovaquone was discontinued after 1 month (financial reasons). It took approximately 6 months to achieve a stable INR, partly due to nonadherence. Two months after a stable therapeutic INR was achieved, atovaquone 1500 mg/day for PCP prophylaxis was restarted. Within 7 days of coadministration, the INR increased from 2.3 to 3.5. Over the next 2 months, the warfarin dose was reduced twice and a dose was withheld due to INR range between 3.1 to 4.2. No signs or symptoms of hemorrhage were reported. Atovaquone was prematurely discontinued again after 2 months, and a day after atovaquone discontinuation, the INR was 1.7. The warfarin dose was adjusted, but no further INRs were obtained before the 12-month course of warfarin was completed. Significant medical history included HIV infection (not on antiretrovirals), past alcohol use (30 beers every weekend and 9 beers every day for the past 7 years), and past marijuana use (30 years). On the Horn Drug Interaction Probability Scale, the interaction was considered probable .
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.
Atovaquone Overview
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Atovaquone is used to treat Pneumocystis jiroveci [Pneumocystis carinii] pneumonia (PCP; type of pneumonia most likely to affect people with human immunodeficiency virus [HIV]) in teenagers and adults. Atovaquone is also used to prevent PCP in teenagers and adults who cannot take another medication used for prevention. Atovaquone is in a class of medications called antiprotozoal agents. It works by stopping the growth of certain types of protozoa that can cause pneumonia.
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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.