Warfarin and Atovaquone: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Jul 11, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Warfarin
Atovaquone
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Increased INR
Interaction Deep Dive
An increased INR was reported in a patient coadministered atovaquone and warfarin. The possible mechanism of interaction is protein binding displacement of warfarin by atovaquone1. Exercise caution when co-administering atovaquone and warfarin due to the potential for increased INR.
Why it happens (mechanism)
Protein displacement of warfarin by atovaquone
Literature reports
1 report — tap to read
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 1.
Common questions
Can I take Warfarin and Atovaquone together?
Increased INR Always confirm with your pharmacist or prescriber before making any change.
How serious is the Warfarin and Atovaquone interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Warfarin or Atovaquone need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (1)
- Hidalgo K, Lyles A, & Dean SR: A potential interaction between warfarin and atovaquone. Ann Pharmacother 2011; 45(1):e3-e3. PubMed
Keep reading about Warfarin
Keep reading about Atovaquone
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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