Hematology and Oncology Book

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Drug Interactions with CoumadinAka: Coumadin Drug Interactions, Warfarin Drug Interactions

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  1. See Also
    1. Coumadin (Warfarin)
    2. Coumadin Protocol
    3. Coumadin Protocol for the Perioperative Period
  2. Drug Interactions: Agents that increase INR or bleeding risk
    1. Acetaminophen (Tylenol)
    2. Alcohol
    3. Amiodarone (Cordarone)
      1. Adjustment per Amiodarone maintenance dose
        1. Amiodarone 400 mg/day: Reduce Warfarin dose 40%
        2. Amiodarone 300 mg/day: Reduce Warfarin dose 35%
        3. Amiodarone 200 mg/day: Reduce Warfarin dose 30%
        4. Amiodarone 100 mg/day: Reduce Warfarin dose 25%
      2. Reference
        1. Sanoski (2002) Chest 121:19
    4. Anabolic Steroids
    5. Antifungal Medications
      1. Fluconazole (Diflucan)
      2. Ketoconazole (Nizoral)
      3. Itraconazole (Sporanox)
      4. Miconazole (Monistat)
    6. Aspirin and Salicylates
    7. Cephalosporins
      1. Cefoperazone (Cefobid)
      2. Cefamandole (Mandol)
      3. Cefotetan (Cefotan)
      4. Cefmetazole (Zefazone)
    8. Chloral Hydrate
    9. Cimetidine (Tagamet)
    10. Clofibrate
    11. Cranberry Juice (CYP2C9 inhibitor)
      1. Appears safe in at least one clinical trial
      2. Greenblatt (2006) Clin Pharmacol Ther 79:125
    12. Danazol (Danocrine)
    13. Diflunisal (Dolobid)
    14. Disulfiram (Antabuse)
    15. Fluvoxamine (Luvox)
    16. Ginkgo Biloba (independent effect due to antiplatelet activity)
    17. Heparin
    18. HMG CoA Reductase inhibitors
    19. Isoniazid (INH)
    20. Macrolides
      1. Erythromycin
      2. Clarithromycin
    21. Metronidazole (Flagyl)
    22. Nalidixic Acid
    23. NSAIDs
    24. Omeprazole (Prilosec)
    25. Paroxetine (Paxil)
    26. Penicillin
    27. Propafenone (Rythmol)
    28. Quinidine
    29. Quinolones
    30. Sulfinpyrazone (Anturane)
    31. Tamoxifen
    32. Tetracycline
    33. Thyroid Hormone (Thyroxine or Synthroid)
    34. Ticlopidine (Ticlid)
    35. Trimethoprim-Sulfamethoxazole (Bactrim, Septra)
    36. Vitamin E
      1. Theoretical bleeding risk, but appears to be safe in clinical trials
      2. Dereska (2006) J Surg Res 132:121
  3. Drug Interactions: Drugs that decrease INR or increase clotting risk
    1. American Ginseng (no effect on Warfarin with Asian Ginseng)
    2. Barbiturates
    3. Binding Resins
    4. Carbamazepine (Tegretol)
    5. Oral Contraceptives
    6. Penicillin
    7. Rifampin
    8. St. John's Wort
    9. Vitamin K
  4. Drugs that have a variable effect on INR or bleeding risk
    1. Allopurinol
    2. Corticosteroids
    3. Phenytoin (Dilantin)
  5. References
    1. Horton (1999) :
    2. Gage (2000) Am J Med 109:484

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