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Warfarin and Vitamin K

Warfarin is an anticoagulant, or blood thinner, used to treat clotting disorders. Doctors prescribe warfarin to prevent the blood from clotting in patients at high risk for clotting disorders, or to prevent further clotting in patients who already have clots. Pulmonary embolus and deep vein thrombosis are two types of life-threatening clots, while atrial fibrillation and certain protein deficiencies are conditions that predispose patients to clots. All these conditions may require anticoagulation.

Warfarin is also sometimes used as a preventative measure, such as following heart valve replacement surgery. It is common for clots to form around the valve. Warfarin thins the blood and inhibits the growth of clots around the new valve.

What Blood Clots Do
Without treatment, blood clots can be fatal. Blood clots can form in the vessels of the heart, lungs and brain, preventing blood flow to these vital organs. When the blood supply to the brain is blocked it is called a stroke. A blocked blood supply in the heart is called a heart attack or myocardial infarction. Blood thinners, like warfarin, slow the ability of blood to clot, preventing the clots from forming.

How Warfarin Works
Anticoagulants work by blocking some aspect of the clotting process. Warfarin acts by reducing levels of vitamin K in the blood. Vitamin K is necessary to activate the coagulation process, so low levels of vitamin K lower the ability of blood to clot.

Achieving the optimal level of vitamin K is not easy, however. Physicians must monitor warfarin therapy frequently with a blood test called the international normalized ratio (INR), which essentially measures the amount of blood thinning. If the INR is too low, the dose of warfarin is ineffective and clots can form. If the INR is too high the blood loses any natural clotting ability and excessive bleeding can occur.

Because vitamin K is a naturally occurring vitamin, diet must also be monitored carefully in patients taking warfarin. Increased consumption vitamin K found in green, leafy vegetables like asparagus, leaf lettuce, broccoli, and cabbage can decrease the effectiveness of warfarin's blood clotting effects and lower the INRs. Other products like Ensure, Boost and Carnation Instant Breakfast also contain vitamin K in amounts high enough to lower INRs and lead to increased clotting. On the other hand, low levels of vitamin K can have the opposite effect on warfarin and increase INRs. Increased INRs can lead to hemorrhaging and other bleeding complications.

Treating Overanticoagulation With Vitamin K
Overanticoagulation occurs when too much warfarin is administered, causing an elevated INR. When the INR is too high, the blood is unable to form any clots and uncontrolled bleeding can occur. In such an event, warfarin doses are usually stopped until the INR value reaches a safe level. Intravenous (IV) or subcutaneous vitamin K can also be administered to reverse the effects of warfarin and restore clotting more quickly.

New studies have shown that vitamin K can also be administered orally in the management of overanticoagulation. In fact, oral vitamin K may actually work faster than subcutaneous injections of vitamin K. The use of vitamin K in cases of overanticoagulation decreases the risk of serious bleeding and hemorrhage.

Resources

Crowther, M., Douketis, J., Schnurr, T., Steidi, L., Mera, V., Ultori, C., Venco, A., Ageno, W. (2002, August 20). Vitamin K reverses overanticoagulation with warfarin more quickly when given by mouth than by injection [electronic version]. Annals of Internal Medicine, 137(4), 1-39. Retrieved December 3, 2003, from
www.annals.org/cgi/content/full/137/4/251.

Glover, J., Morrill, G. (1995, October) Conservative treatment of overanticoagulated patients [electronic version]. Chest, 108(4), 987-990 retrieved December 3, 2003, from www.chestjournal.org/cgi/reprint/108/4/987.pdf.

Warfarin.com. (2003, November 21). Indications. Retrieved December 3, 2003, from www.warfarinfo.com/indications.htm.

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