What medications can interact with warfarin (Coumadin)?

Foods containing vitamin K affect how Coumadin works. Green leafy vegetables contain a high level of vitamin K. Increased consumption of vitamin K containing foods decrease the blood thinning effect of Coumadin. Reducing the consumption of vitamin K containing foods will increase the effect of Coumadin. To avoid a yo-yo effect in the action of Coumadin, healthcare providers suggest that vitamin K consumption should not vary widely while on Coumadin treatment.

Mohammad Mortada, MD
Cardiology (Cardiovascular Disease)
It is important to keep in mind that several medications can change the effect of warfarin (Coumadin).

Medications or substances that increase INR and risk of bleeding include:
  • Antiarrhythmic medications: amiodarone, propafenone
  • Antibiotics: azithromycin (Zmax, Zithromax), cefazolin (Ancef,
           Kefzol), erythromycin (E-mycin, Ery-Tab, Eryc, E.E.S.,
           Erythrocin), aspirin
  • Alcohol in beverages or cough medicines
  • Beta-adrenergic blockers: propranolol (Inderal)
  • Diabetic agents
  • Herbal supplements
  • Thyroid drugs
Medications that decrease INR and increase the risk of stroke include:
  • Antacids
  • Antianxiety agents
  • Antibiotics: dicloxacillin (Dynapen), nafcillin
  • Cortisone (Cortef)
  • Oral contraceptives
  • Spironolactone (Aldactone)
  • Vitamin C (high dose)
  • Vitamin K (green, leafy vegetables)
Medications or substances that have unpredictable effects:
  • Alcohol
  • Antidepressants
  • Gastric acidity and peptic ulcer agents

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