Gemcitabine and Warfarin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Warfarin
Gemcitabine
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
An increased risk of bleeding
Interaction Deep Dive
Two case reports describe patients receiving stable doses of warfarin and experiencing increases in INR with the initiation of gemcitabine. One patient experienced critically elevated INR that peaked at 8.6 and led to hematomas with intravesicular gemcitabine. Treatment with phytonadione was required and warfarin was permanently discontinued1. Another patient required reductions in his warfarin dose to maintain the INR in the target range. Following the discontinuation of gemcitabine, the warfarin dose required an upward titration to its previous level 2.
Why it happens (mechanism)
Reversible hepatotoxicity, reducing warfarin metabolism and decreasing hepatic synthesis of clotting factors
Literature reports
2 reports — tap to read
a) A 90-year-old man receiving warfarin 4 mg/day for 2 months for DVT (stable INR, 2 to 3) was initiated on intravesicular gemcitabine 2 g for bladder cancer and experienced critically elevated INR that peaked at 8.6 and led to hematomas. INR was within therapeutic range after the second gemcitabine cycle, but by the end of the 4th cycle, was elevated to 7.4. CT scan of the abdomen and pelvis revealed a left psoas hematoma and a small left pectineus hematoma. Warfarin was permanently discontinued, the patient received phytonadione 5 mg orally, the INR fell to 1.8, and the patient was discharged on enoxaparin. The interaction on the Horn Drug Interaction Probability Scale was assessed as probable with a score of 6 1.
b) A 63-year-old man stabilized on warfarin 57.5 mg/week (INR 1.94) for atrial fibrillation was diagnosed with stage IV non-small cell lung cancer. Treatment with gemcitabine 2380 mg weekly for 3 weeks, followed by a 2-week rest period, was initiated. The INR increased to 3.52 following the first dose of gemcitabine. The warfarin was decreased to 52.5 mg/week, and the INR decreased to 2.08 and 2.13 during the 2-week rest period from gemcitabine. During the second cycle of gemcitabine, the INR rose to 3.58 despite the warfarin being decreased to 50 mg/week. Warfarin was further decreased to 48.5 mg/week to achieve a therapeutic INR of 2.2. Gemcitabine was discontinued after the second cycle, and the subsequent INR values were subtherapeutic. Warfarin required an upward titration back to the baseline of 57.5 mg/week. The patient experienced no emesis or weight loss as a result of gemcitabine therapy, and no antiemetics were given 2.
Common questions
Can I take Gemcitabine and Warfarin together?
An increased risk of bleeding Always confirm with your pharmacist or prescriber before making any change.
How serious is the Gemcitabine and Warfarin interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.
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 Gemcitabine or Warfarin 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 a safer alternative to one of these medications for me?
References (2)
- Kurtzhalts K, Gee ME, Feuz L, et al: Evidence of a clinically significant interaction between warfarin and intravesical gemcitabine. Am J Health Syst Pharm 2016; 73(19):1508-1511. PubMed
- Kinikar SA & Kolesar JM: Identification of a gemcitabine-warfarin interaction. Pharmacotherapy 1999; 19:1331-1333. PubMed
Keep reading about Warfarin
Keep reading about Gemcitabine
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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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