Warfarin - Wikipedia. This article is about the anticoagulation medication. For the rodenticide often called . Less common side effects may include tissue death and purple toes syndrome. Use is not generally recommended during pregnancy. It is recommended that the effects of warfarin typically be monitored by checking prothrombin time every one to four weeks. Warfarin treatment can help prevent formation of future blood clots and help reduce the risk of embolism (migration of a thrombus to a spot where it blocks blood supply to a vital organ). Thus, common clinical indications for warfarin use are atrial fibrillation, the presence of artificial heart valves, deep venous thrombosis, and pulmonary embolism (where the embolized clots first form in veins). Warfarin is also used in antiphospholipid syndrome. It has been used occasionally after heart attacks (myocardial infarctions), but is far less effective at preventing new thromboses in coronary arteries. Prevention of clotting in arteries is usually undertaken with antiplatelet drugs, which act by a different mechanism from warfarin (which normally has no effect on platelet function). These have a shorter (acenocoumarol) or longer (phenprocoumon) half- life, and are not completely interchangeable with warfarin.
Several types of anticoagulant drugs offering the efficacy of warfarin without a need for monitoring, such as dabigatran, apixaban, edoxaban and rivaroxaban, have been approved in a number of countries for classical warfarin uses like the more common types of atrial fibrillation, and others in the same drug classes are under development. There is a reversal agent available for dabigatran (idarucizumab). To optimize the therapeutic effect without risking dangerous side effects such as bleeding, close monitoring of the degree of anticoagulation is required by a blood test measuring an INR. During the initial stage of treatment, INR is checked daily; intervals between tests can be lengthened if the patient manages stable therapeutic INR levels on an unchanged warfarin dose. Instead of a blood draw, the point of care test involves a simple finger prick. The target INR level varies from case to case depending on the clinical indicators, but tends to be 2. In particular, target INR may be 2. Therefore, bridging anticoagulant therapies (usually heparin) are often used to reverse this temporary hypercoagulable state. Maintenance dose. When warfarin levels are high, people have more risk of bleeding. Conversely, lower levels of warfarin lead to increased risk of blood clots. There is a narrow range where the benefits of warfarin are greater than the risks, its therapeutic window. Certain drugs, herbal medicines and foods can interact with warfarin, increasing or decreasing a previously stable warfarin level. Keeping vitamin K1 intake at a stable level can prevent these fluctuations. Leafy green vegetables tend to contain higher amounts of vitamin K1. Green parts of members of the family Apiaceae, such as parsley, cilantro, and dill, are extremely rich sources of vitamin K; cruciferous vegetables such as cabbage and broccoli, as well as the darker varieties of lettuces and other leafy greens, are also relatively high in vitamin K1. Green vegetables such a peas and green beans do not have such high amounts of vitamin K1 as leafy greens. Certain vegetable oils have high amounts of vitamin K1. Foods low in vitamin K1 include roots, bulbs, tubers, and most fruits and fruit juices. Cereals, grains and other milled products are also low in vitamin K1. International guidelines on home testing were published in 2. All patients must be appropriately selected and trained. Currently available self- testing/self- management devices give INR results that are comparable with those obtained in laboratory testing. With heparin, risk of maternal haemorrhage and other complications are still increased, but heparins do not cross the placental barrier, so do not cause birth defects. FWS is characterized mainly by skeletal abnormalities, which include nasal hypoplasia, a depressed or narrowed nasal bridge, scoliosis, and calcifications in the vertebral column, femur, and heel bone, which show a peculiar stippled appearance on X- rays. Limb abnormalities, such as brachydactyly (unusually short fingers and toes) or underdeveloped extremities, can also occur. The most common congenital abnormalities associated with warfarin use in late pregnancy are central nervous system disorders, including spasticity and seizures, and eye defects. Similarly, INR levels should be checked to avoid adverse effects. The risk of severe bleeding is small but definite (a typically yearly rate of 1- 3% has been reported). All types of bleeding occur more commonly, but the most severe ones are those involving the brain (intracerebral hemorrhage/hemorrhagic stroke) and the spinal cord. A commonly used score (HAS- BLED) includes known predictors of warfarin- related bleeding: uncontrolled high blood pressure (H), abnormal kidney function (A), previous stroke (S), known previous bleeding condition (B), previous labile INR when on anticoagulation (L), elderly as defined by age over 6. E), and drugs associated with bleeding (e. While their use is recommended in clinical practice guidelines. Protein C is an innate anticoagulant that, like the procoagulant factors that warfarin inhibits, requires vitamin K- dependent carboxylation for its activity. Since warfarin initially decreases protein C levels faster than the coagulation factors, it can paradoxically increase the blood's tendency to coagulate when treatment is first begun (many patients when starting on warfarin are given heparin in parallel to combat this), leading to massive thrombosis with skin necrosis and gangrene of limbs. Its natural counterpart, purpura fulminans, occurs in children who are homozygous for certain protein C mutations. A 1. 99. 9 study in 5. The mechanism was thought to be a combination of reduced intake of vitamin K, which is necessary for bone health, and inhibition by warfarin of vitamin K- mediated carboxylation of certain bone proteins, rendering them nonfunctional. This condition is thought to result from small deposits of cholesterol breaking loose and causing embolisms in blood vessels in the skin of the feet, which causes a blueish purple colour and may be painful. It is typically thought to affect the big toe, but it affects other parts of the feet as well, including the bottom of the foot (plantar surface). The occurrence of purple toe syndrome may require discontinuation of warfarin. No specific treatment is available, but some modalities are under investigation. Risk of bleeding is increased if the INR is out of range (due to accidental or deliberate overdose or due to interactions). When warfarin is being given and INR is in therapeutic range, simple discontinuation of the drug for five days is usually enough to reverse the effect and cause INR to drop below 1. This increased risk is due to the anti- platelet effect of NSAIDS as well as the possible damage to the gastrointestinal mucosa. Other broad- spectrum antibiotics can reduce the amount of the normal bacterial flora in the bowel, which make significant quantities of vitamin K1, thus potentiating the effect of warfarin. Food and Drug Administration (FDA) product insert on warfarin states that alcohol should be avoided. Warfarin sodium is the active ingredient in COUMADIN. Diet plans, nutrition. These Ingredients Make Rat Poison So Lethal and Effective. Rodents infest homes. Coumadin, Jantoven, Marevan, others. All may increase bleeding and bruising in people taking warfarin; similar effects have been reported with borage (starflower) oil or fish oils. John's Wort, sometimes recommended to help with mild to moderate depression, reduces the effectiveness of a given dose of warfarin; it induces the enzymes that break down warfarin in the body, causing a reduced anticoagulant effect. S- warfarin is 2- 5 times more potent than the R- isomer in producing an anticoagulant response. Heparin must be given by injection, whereas warfarin is available orally. Warfarin has a long half- life and need only be given once a day. Heparin can also cause a prothrombotic condition, heparin- induced thrombocytopenia (an antibody- mediated decrease in platelet levels), which increases the risk for thrombosis. It takes several days for warfarin to reach the therapeutic effect since the circulating coagulation factors are not affected by the drug (thrombin has a half- life time of days). Warfarin's long half- life means that it remains effective for several days after it was stopped. Furthermore, if given initially without additional anticoagulant cover, it can increase thrombosis risk (see below). For these main reasons, hospitalised patients are usually given heparin with warfarin initially, the heparin covering the 3. The precursors of these factors require gamma carboxylation of their glutamic acid residues to allow the coagulation factors to bind to phospholipid surfaces inside blood vessels, on the vascular endothelium. The enzyme that carries out the carboxylation of glutamic acid is gamma- glutamyl carboxylase. The carboxylation reaction will proceed only if the carboxylase enzyme is able to convert a reduced form of vitamin K (vitamin K hydroquinone) to vitamin K epoxide at the same time. The vitamin K epoxide is in turn recycled back to vitamin K and vitamin K hydroquinone by another enzyme, the vitamin K epoxide reductase (VKOR). Warfarin inhibits epoxide reductase. When this occurs, the coagulation factors are no longer carboxylated at certain glutamic acid residues, and are incapable of binding to the endothelial surface of blood vessels, and are thus biologically inactive. As the body's stores of previously produced active factors degrade (over several days) and are replaced by inactive factors, the anticoagulation effect becomes apparent. The coagulation factors are produced, but have decreased functionality due to undercarboxylation; they are collectively referred to as PIVKAs (proteins induced . The end result of warfarin use, therefore, is to diminish blood clotting in the patient.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
July 2017
Categories |