Edited by Joe Hing Kwok Chu
Trade names: Coumadin, Panwarfin, Warfilone, Warfarin.
See Chemical structure here.
The name Warfarin was derived from Wisconsin Alumni Research Foundation and Coumarin, and was synthesized and used as a rodenticide for nearly a decade prior to its 1954 introduction into clinical medicine.
Usually the sodium salt is used. It is a white crystal powder with no smell and with some bitter taste. It is water soluble and alcohol soluble. It is almost insoluble in chloroform or in ether.
Therapeutic Class: Anticoagulants, Anti platelet Agents
Effective prevention of both arterial and venous thrombosis
Effective prevention of embolization in thromboembolic disorders
Helps prevent recurrence of heart attacks
Helps prevent strokes in patients with atrial fibrillation
Narrow treatment range
Dose related bleeding
Skin and soft tissue hemorrhage with tissue death
Medical function: The anticoagulants interfere with the hepatic synthesis of four essential vitamin K-dependent coagulation proteins or blood clotting factors I, VII, IX, and X by competing with and blocking the action of vitamin K, thus causing the production of those factors that lack clotting ability. Wafarin does not work outside the body. When taken internally its anticoagulation effect shows only when the previously formed blood clotting factors I, VII, IX, and X have been depleted. Because of this, heparin can be used in the early stage of using warfarin (Coumadin).(1)
Usage: For patients with a mechanical heart valve, an INR of 2.5~3.5 is now recommended. An INR of 2~3 remains the recommended intensity of warfarin therapy to prevent thromboembolism in all other patients.
Patient information: do not take with food; report any signs of bleeding; avoid hazardous activities; use soft tooth brush; urine may turn red/orange; carry Medi-Alert ID identifying drug usage; be sure of other drugs and dietary changes to avoid; report any bleeding to physician at once. There are no food or fluid restrictions before the PT or APTT tests. (2)
Long term usage can cause nose bleeding, gum bleeding, purpura, blood in urine, uterine bleeding, blood in stool, bleeding of ulcers and wounds. Without tests of PT and APTT, the use of warfarin is not recommended.
Do not use in cases of hemophilia, idiopathic thrombocytopenic purpura, serious liver or kidney problems, active peptic ulcer, brain, spine or eye surgery. Overdose of warfarin causes idiopathic bleeding. Symptoms: mucus bleeding (blood in urine, bleeding in the digestive track), bleeding in the joints, bleeding in the wounds.
Use care when the following conditions exist: weakness, fever, chronic alcoholism, active TB, congestive heart failure, hypertension, sub-acute bacterial endocarditis, heavy bleeding during menses, symptomatic miscarriage .
During prolonged usage with minimum dosage, if surgery is required a vein injection of vitamin K of 50 mg is recommended. Before surgery on central nervous system or eyes, stopping use of warfarin in advance is recommended. After digestive track surgery, it is important to test stool for heme.
Food that can affect warfarin: Large intake of the following foods may impair the function of warfarin and make it necessary to use larger dosages:
Foods rich in vitamin K include:
green leafy vegetables.
However, contrary to popular belief, people on warfarin do not have to avoid foods with high vitamin K because the dosage of warfarin can be adjusted for the level of dietary vitamin K intake. It is better to eat the same amount of every day so that the level of thinning effect remains stable.
USDA site on vitamin K food list
Vitamin E may increase risk of bleeding.
Alcohol: Heavy users of alcohol with liver damage may be very sensitive to anticoagulants and require smaller than usual doses.
Tobacco Smoking: Heavy users may require larger doses of warfarin (Coumadin). Quit smoking.
Warfarin may increase the effects of :
oral hypoglycemic agents:
See list of drugs may increase the effects of warfarin.
See list of herbs may increase the effects of warfarin.
See list of drugs may decrease the effects of warfarin:
Note: Coenzyme Q is structurally related to vitamin K (menaquinone); therefore, it possesses pro-coagulant properties.
Do not stop warfarin abruptly unless bleeding occurs.
Dosage: Tablet: 1 mg, 2 mg, 2.5 mg, 5 mg, 7.5 mg, 10 mg. Injection: 5 mg
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