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Selected warfarin drug-drug interactions
Contains many of the typical agents, however, there may be some omissions.
Decreased effect (lower INR) |   Increased INR/Potentiation  |
Drug-food interactions |
Agents that may increase bleeding risk
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Warfarin related Links

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Decreased warfarin effect (Lower INR)

Drugs: Selected herbals:
Amobarbital
Butabarbital
Carbamazepine
Cholestyramine
Dicloxacillin
Griseofulvin
Mercaptopurine
Mesalamine
Nafcillin
Phenobarbital
Phenytoin
Primidone
Ribavirin
Rifabutin
Rifampin
Secobarbital
Sucralfate
Vitamin K
Coenzyme Q10
Ginseng
St. John’s wort
Green tea

Increased warfarin effect (POTENTIATION)

Drugs: Selected herbals:
Acetaminophen
Alcohol (binge)
Allopurinol
Amiodarone
Argatroban
Aspirin
Azithromycin
Bactrim
Chloral hydrate
Chloramphenicol
Cimetidine
Ciprofloxacin
Citalopram
Clarithromycin
Clofibrate
Danazol
Diltiazem
Disopyramide
Disulfiram
Doxycycline
Entacapone
Erythromycin
Felbamate
Fenofibrate
Fluconazole
Fluorouracil
Fluvoxamine
Gemfibrozil
Influenza vaccine
Isoniazid
Itraconazole
Levofloxacin
Metronidazole
Miconazole
Moxalactam
Neomycin
Norfloxacin
Ofloxacin
Omeprazole
Phenylbutazone
Piroxicam
Propafenone
Propranolol
Quinidine
Ritonavir
Sertraline
Simvastatin
Sulfamethoxazole
Sulfinpyrazone
Tamoxifen
Testosterone
Tetracycline
Vitamin E
Voriconazole
Zafirlukast
Anise
Asafoetida
Chamomile
Clove
Danshen
Devil’s claw
Dong quai
Fenugreek
Feverfew
Fish oil
Garlic
Ginger
Ginkgo
Grapefruit
Horse chestnut
Licorice root
Mango
Meadowsweet
Onion
Papain
Quassia
Red clover
Rue
Sweet clover
Tumeric
Willow bark
Vitamin E

Warfarin – Food Interactions

Management of Dietary Interactions and Vitamin K: dietary consistency is the key to maintaining a sustained, stable response during warfarin therapy. Patients should be aware of vitamin K content in common foods, particularly foods high in vitamin K (green leafy vegetables: broccoli, Brussel sprouts, turnip greens, kale, spinach, beet greens), Cauliflower, legumes, mayonnaise, canola and soybean oils), and should maintain a consistent amount of these foods in their diet.

The following foods should be avoided or limited, since they also can effect warfarin therapy: caffeinated beverages (cola, coffee, tea, hot chocolate, chocolate milk).

Alcohol intake greater than 3 drinks daily can increase the effect of Coumadin. As long as alcohol intake does not exceed 3 drinks daily, clotting times should not be affected. This amount of alcohol is present in 12 ounces of table wine or three 12 ounce beers. (Acute binges can raise INR. Chronic alcohol ingestion may decrease INR. )

Herbal supplements can affect bleeding time. Coenzyme Q10 is an herbal supplement whose chemical structure is similar to vitamin K, so it has the potential to affect bleeding time. Herbal teas: green tea, buckeye, horsechestnut, tonka, bean, meliot, and woodruff. Other examples include: feverfew, garlic, and ginseng. Herbal medications should either be avoided or used consistently while on warfarin therapy.

Increased bleeding risk

Drugs:
Aspirin
Clopidogrel
Danaparoid
Dipyridamole
LMWHs
NSAIDs
Ticlopidine
Unfractionated heparin
Selected warfarin drug-drug interactions