To Bleed or Not To Bleed: Moderation Is The Key To Hemostasis
Warfarin (Coumadin) is a compound of significant medical importance. Over the last 40 years, thousands have used it safely and effectively, to prevent strokes, heart attacks, deep venous thrombosis and pulmonary emboli. The main mechanism of action is inhibition of the action of Vitamin K, which promotes the formation of some clotting proteins.
The PT or prothrombin time measures the tendency of the blood to clot as compared with a control sample. It is expressed as the number of seconds it takes for the blood to clot, or may be expressed as a ratio of the blood sample to the control.
The INR or International Normalized Ratio is a more accurate expression of the action of warfarin as it expresses the speed of blood clotting by correcting for inconsistencies in the control samples. It is currently recommended that the INR be used to adjust dosages of warfarin. For most conditions, the INR is optimally kept in the range of 2.0-4.0. This range is determined by the prescribing physician.
Warfarin has a large number of interactions with other drugs, some of which increase it’s effects, others which decrease them. The most important drug interactions are with asprin, non-steroidal anti-inflammatory agents and some antibiotics. Aspirin inhibits the clotting functions of platelets, and non-steroidal anti-inflammatory agents may interfere with the metabolism of warfarin. Some antibiotics react with the way warfarin is carried in the blood, interfere with warfarin metabolism in the liver, or alter the metabolism of Vitamin K.
Diet is extremely important in warfarin therapy. This is because the synthesis of the clotting factors in the liver depends on the availability of Vitamin K. Therefore, the amount of Vitamin K in the diet can affect the action of warfarin. Until fairly recently, doctors advised people taking warfarin to avoid foods high in vitamin K, to avoid the possibility of large amounts of vitamin K counteracting the benefits of warfarin. However, recent research shows that rather than eliminating vitamin K from the diet, it is more important to be consistent in dietary vitamin K intake. Wide swings in intake may cause the PT/INR to change a significant amount. Patients should be made aware of foods that are particularly high in Vitamin K, and try to keep the amounts fairly constant.
The USDA has the best list of foods with vitamin K. Large amounts of vitamin K are found in foods such as liver, broccoli, brussels sprouts, spinach, Swiss chard, coriander, collards, cabbage, and other green leafy vegetables. Certain beverages can also increase the effect of warfarin, such as cranberry juice, green tea and alcohol. Patients should be instructed to choose foods that add up to less than the RDA (Recommended Dietary Allowance) for vitamin K, and be consistent in the daily amounts ingested from day to day. The average recommended daily allowance of vitamin K for adult men is 120 mcg. For adult women, it's 90 mcg.
The key to success sees to lie in consistency and moderation. By avoid sudden changes in Vitamin K consumption, the effects of coumadin on the body will be more stable.