What decreases the effectiveness of warfarin?
If you are taking warfarin, the amount of vitamin K in your diet may affect how well the medicine works. If you take warfarin, it's important to have a consistent amount of vitamin K in your diet. Too little vitamin K can increase your risk of bleeding. Too much vitamin K can decrease warfarin's anti-clotting ability.
What inhibits warfarin metabolism?
Acutely, drinking more alcohol will inhibit the metabolism of warfarin, but chronic use of alcohol can induce liver enzymes and result in a lower INR.  Ongoing alcohol use is a concern for the risk of gastrointestinal bleeding, which will complicate anticoagulation management.
What can potentiate the effects of warfarin?
Warfarin's anticoagulant effect was potentiated by 6 antibiotics (cotrimoxazole, erythromycin, fluconazole, isoniazid, metronidazole, and miconazole); 5 cardiac drugs (amiodarone, clofibrate, propafenone, propranolol, and sulfinpyrazone); phenylbutazone; piroxicam; alcohol (only with concomitant liver disease);
Foods with high levels of vitamin K include kale, broccoli, and Brussels sprouts. Other changes to your nutrition, such as starting a new diet or taking new supplements, can also cause your INR level to fluctuate. Talk to your doctor before starting any new diet/nutrition regimens.
With an increase in vitamin K , your INR level may drop. Conversely, a decrease in vitamin K intake may increase the INR. Other things, like medications, antibiotics, and herbal products may also influence your INR.
Foods to limit while taking warfarin
The AHA'a list of 19 foods high in vitamin K includes:
So, go bananas! But be sure to eat green bananas in normal portions and make sure you keep testing your regular blood test to make sure your INR doesn't drop below your target range.
Warfarin is highly protein-bound (>95%) and has a low therapeutic index. Since a low therapeutic index indicates that there is a high risk of toxicity when using the drug, any potential increases in warfarin concentration could be very dangerous and lead to hemorrhage.
The CYP2C9 enzyme breaks down (metabolizes) compounds including steroid hormones and fatty acids. The CYP2C9 enzyme also plays a major role in breaking down the drug warfarin, which thins the blood and prevents blood clots from forming.
Examples of Common Drug-Drug Interactions Involving the Cytochrome P450 Enzyme System
|Drug(s)/product||Enzyme inhibitor or inducer||Drug(s)|
|Amiodarone (Cordarone)||CYP2C9 and CYP3A4 inhibitor||Warfarin (Coumadin)|
|Carbamazepine (Tegretol), phenobarbital, phenytoin (Dilantin)||CYP3A4 inducer||Ethinyl estradiol-containing contraceptives|
Warfarin is most commonly discontinued because of physician preference, patient refusal, and bleeding events.
The S-enantiomer exhibits 2 to 5 times more anticoagulant activity than the R-enantiomer in humans, but generally has a more rapid clearance. COUMADIN is essentially completely absorbed after oral administration with peak concentration generally attained within the first 4 hours.
If similar differences in the absorption of the isomers would be demonstrated, it could account for an apparent lack of response in some patients. Generally, warfarin is rapidly and completely absorbed from the gastrointestinal tract after oral administration.
The most common foods that have high vitamin K are green leafy vegetables such as kale, collard greens, broccoli, spinach, cabbage, and lettuce. Other foods that could affect warfarin may include beef liver or other animal liver products.
To keep your INR stable and within the recommended range it is important to: Eat the same number of servings of high Vitamin K foods each week. A good rule is, the greener the plant the higher the Vitamin K level.
Normal and Critical Findings
For patients who are on anticoagulant therapy, the therapeutic INR ranges between 2.0 to 3.0. INR levels above 4.9 are considered critical values and increase the risk of bleeding.
No significant difference in the relationship between INR level and fasting glucose was shown by Pearson test (r = 0.070, P = 0.184).
If the patient is asymptomatic and the low level is picked up on a routine lab draw, then the treatment can range from simply monitoring the level if slightly low, increasing the patient's oral intake of Vitamin K in diet or increasing the dose of the patient's anticoagulant.
Your test results may also be affected by: Severe diarrhea or vomiting that causes fluid loss and dehydration. This may increase the INR.
Keep in mind, you may have other dietary restrictions based on your individual medical conditions. Foods you can eat on a warfarin diet: Meat, fish, eggs. Milk, cheese, yogurt.
10 Dairy Foods and Eggs High in Vitamin K
Dairy foods and eggs are decent sources of vitamin K2. Just like meat, their vitamin content depends on the animal's diet, and values vary by region or producer.
The study examined the vitamin K content in milk, cheese and yogurt and found the amount of vitamin K2 in a dairy food is proportional to the amount of fat in the food. For example, fuller-fat varieties of cheese contain the most vitamin K2, while lower-fat varieties contain less.
Research has shown that certain fruits, particularly grapefruit and other citrus juices, can interfere with medication efficacy.
Because you are taking a blood thinner, you should try not to hurt yourself and cause bleeding. You need to be careful when you use knives, scissors, razors, or any sharp object that can make you bleed. You also need to avoid activities and sports that could cause injury. Swimming and walking are safe activities.
Menu planning for patients on warfarin can include a healthy diet including fruits and nuts without compromising the stability of their oral anticoagulation therapy.
No interactions were found between Vitamin D3 and warfarin.
who originally reported that increased physical activity is inversely associated with decreased INR in three warfarin stabilized patients . The warfarin pharmacokinetic interaction with physical activity could be attributable to different mechanisms.
Blood-thinning foods, drinks, and supplements
The elimination of warfarin is almost entirely by metabolism with a small amount excreted unchanged. 80% of the total dose is excreted in the urine with the remaining 20% appearing in the feces. R-warfarin is cleared more slowly than S-warfarin, at about half the rate. T1/2 for R-warfarin is 37-89 hours.
Warfarin decreases blood clotting by blocking an enzyme called vitamin K epoxide reductase that reactivates vitamin K1. Without sufficient active vitamin K1, clotting factors II, VII, IX, and X have decreased clotting ability.
It's usual to take warfarin in the evening. This is so that if you need to change the dose after a routine blood test, you can do this the same day rather than waiting until the following morning. Warfarin does not usually upset your stomach, so you can take it whether you have eaten recently or not.
Warfarin resistance is a rare condition in which people have varying degrees of tolerance to the anticoagulant drug warfarin. In incomplete warfarin resistance, people only respond to high doses of warfarin; in complete warfarin resistance, the drug has no effect.
Warfarin works against vitamin K, making your blood clot more slowly.
The anticoagulant drug warfarin occurs as a pair of enantiomers that are differentially metabolized by human cytochromes P450 (CYP). R-warfarin is metabolized primarily by CYP1A2 to 6- and 8-hydroxywarfarin, by CYP3A4 to 10-hydroxywarfarin, and by carbonyl reductases to diastereoisomeric alcohols.
The authors conclude that American ginseng reduced the anticoagulant effect of warfarin by induction of hepatic P450 enzyme system activity and increased warfarin elimination.
Heparin. Heparin works faster than warfarin, so it is usually given in situations where an immediate effect is desired. For example, this medication is often given in hospitals to prevent growth of a previously detected blood clot.