As a nutrition support pharmacist, you should discuss with your patients who take warfarin (Marevan) about the interaction with food. Many patients are caught by surprise when fad diets or special foods interfere with their warfarin therapy. Most patients know that green leafy vegetables and other foods with high vitamin K can decrease warfarin's efficacy, (see table 1). Now several other dietary interactions are being recognized...
Atkins, South Beach diets. High-protein, low-carb diets seem to increase albumin, which binds to warfarin. Less warfarin is available for anticoagulation, leading to lower INR. These diets might also induce liver enzymes, increasing warfarin metabolism. Both mechanisms can require a warfarin dose INCREASE to maintain target INR.
| Table (1). Vitamin K Content of Selected Foods | |||
|---|---|---|---|
| Foods | Low | Moderate | High |
| Vegetables | |||
| |
Green beans | Asparagus | Broccoli |
| Carrots | Avocado | Brussels sprouts | |
| Cauliflower | Red Cabbage | Cabbage | |
| Celery | Green peas | Collard greens | |
| Corn | Endive (raw) | ||
| Cucumber (peel removed) | Pickle (dill) | Kale (raw leaf) | |
| Eggplant | Lettuce (iceberg) | Lettuce (bib, red leaf) | |
| Mushrooms | Mustard greens (raw) | ||
| Onions | Parsley | ||
| Green pepper | Spinach | ||
| Potato | Turnip greens (raw) | ||
| Pumpkin | Watercress (raw) | ||
| Sauerkraut (canned) | Swiss chard | ||
| Tomato | |||
| Fruits | |||
| |
Apple | ||
| Banana | |||
| Blueberries | |||
| Grapes | |||
| Orange | |||
| Meats | |||
| |
Beef | ||
| Chicken | |||
| Pork | |||
| Tuna | |||
| Turkey | |||
| Fats and Oils | |||
| |
Corn oil | Margarine | Mayonnaise |
| Peanut oil | Olive oil | Canola oil | |
| Safflower oil | Soybean oil | ||
| Sesame oil | |||
| Sunflower oil | |||
| Dairy Products | |||
| |
Butter | ||
| Cheese (cheddar) | |||
| Eggs | |||
| Sour cream | |||
| Yogurt | |||
| Beverages | |||
| |
Coffee | ||
| Cola | |||
| Fruit juices | |||
| Milk | |||
| Tea (black) | Tea (green) There is some controversy as to whether brewing green tea alters the vitamin K content and/or whether green tea may alter the effect of warfarin by some other mechanism |
||
| Adapted with permission from Clotcare Online Resource at www.clotcare.com... | |||
Cranberries contain flavonoids that may inhibit CYP2C9 that metabolizes warfarin. This could INCREASE warfarin's effect. Garlic has antiplatelet effects can increase bleeding risk in warfarin patients. Tell warfarin patients not to consume more than one clove of garlic daily, UNLESS they've been doing it all along and their INR is pretty stable.
Alcohol, more than three drinks/day can INCREASE INR in most people, but CHRONIC alcohol abuse tends to DECREASE INR. Green tea and soy protein contain a lot of vitamin K, but brands vary widely. Watch for decreased or fluctuating INRs. Grapefruit, findings are inconsistent, but grapefruit may interfere with warfarin metabolism. More than 24 ounces of grapefruit juice daily may INCREASE INR. Finally, remind warfarin patients that CONSISTENCY is key. Advise them to stick with a steady diet. Check INR with ANY diet change. Get our note, "Drug interactions between warfarin and many antimicrobials".
References
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Kalvass JC, Phinney SD, Vernon MC, Rosedale R, Westman EC. Comment: Decreased warfarin effect after initiation of high-protein, low-carbohydrate diets. Ann Pharmacother. 2005 Jul-Aug;39(7-8):1371-2; author reply 1372. Available at: https://pubmed.ncbi.nlm.nih.gov/15928257/, OR https://journals.sagepub.com/doi/10.1345/aph.1E454b
Cambria-Kiely JA. Effect of soy milk on warfarin efficacy. Ann Pharmacother. 2002 Dec;36(12):1893-6. Available at: https://pubmed.ncbi.nlm.nih.gov/12452752
Taylor JR, Wilt VM. Probable antagonism of warfarin by green tea. Ann Pharmacother. 1999 Apr;33(4):426-8. Available at: https://pubmed.ncbi.nlm.nih.gov/10332534
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