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- What is warfarin, and how does it work (mechanism of action)?
- What brand names are available for warfarin?
- Is warfarin available as a generic drug?
- Do I need a prescription for warfarin?
- What are the uses for warfarin?
- What are the side effects of warfarin?
- What is the dosage for warfarin?
- Which drugs or supplements interact with warfarin?
- Is warfarin safe to take if I'm pregnant or breastfeeding?
- What else should I know about warfarin?
What is warfarin, and how does it work (mechanism of action)?
- Warfarin is an oral anticoagulant, a drug that inhibits the clotting of blood. It prevents the formation of blood clots by reducing the production of factors by the liver that promote clotting, factors II, VII, IX, and X, and the anticoagulant proteins C and S. The production of these factors by the liver are dependent on adequate amounts of vitamin K. Warfarin reduces the production of the factors because it antagonizes vitamin K. Blood clots can occur in the veins of the lower extremities (deep venous thrombosis [DVT]), often after periods of immobility. These clots can break off and become lodged in the blood vessels of the lung (pulmonary embolism), causing shortness of breath, chest pain, and even life-threatening shock. Blood clots can also occur in the atria of the heart during atrial fibrillation and around artificial heart valves. These clots also can break off and obstruct blood vessels in the brain, causing an embolic stroke with paralysis. Warfarin is important in preventing the formation of blood clots, preventing extension of clots already formed, and minimizing the risk of embolization of blood clots to other vital organs such as the lungs and brain.
- The FDA approved warfarin in June 1954.
What are the uses for warfarin?
- Warfarin is used in treating patients with deep vein thrombosis (DVT) to prevent extension of the clot, and to reduce the risk of pulmonary embolism.
- Patients with pulmonary embolism are treated with warfarin to prevent further emboli.
- Warfarin also is used in patients with atrial fibrillation or artificial heart valves to reduce the risk of strokes, and after a heart attack.
- It also is helpful in preventing blood clots from forming in certain orthopedic surgeries such as knee or hip replacements.
- Warfarin is used in preventing closure of coronary artery stents due to clotting.
What are the side effects of warfarin?
The two most serious side effects of warfarin are:
- Necrosis (gangrene) of the skin
Bleeding can occur in any organ or tissue. Bleeding around the brain can cause severe headache and paralysis. Bleeding in the joints can cause joint pain and swelling. Bleeding in the stomach or intestines can cause weakness, fainting spells, black tarry stools, vomiting of blood, or coffee ground material. Bleeding in the kidneys can cause back pain and blood in urine.
Other side effects include:
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What is the dosage for warfarin?
- Warfarin may be taken with or without food.
- Since warfarin is metabolized (inactivated) by the liver and then excreted by the kidneys, dosages need to be lowered in patients with liver and kidney dysfunction.
- Frequent blood tests (INR test) are performed to measure the effect of warfarin and to adjust dosing.
- There are published INR ranges for the various uses of warfarin.
- Treatment usually is started at 2 to 5 mg once daily and the dose is adjusted based in INR tests.
- Patients typically require 2 to 10 mg of warfarin daily.
Which drugs or supplements interact with warfarin?
- Many drugs, both prescription and nonprescription (OTC), can affect the anticoagulant action of warfarin or increase the risk of bleeding. Patients on warfarin should regularly consult their doctor before instituting any medications on their own.
- It also is advisable for patients on warfarin to carry identification such as bracelets to alert other health professionals to the presence of anticoagulation.
- A few examples of drugs that interact with warfarin are:
- Drugs that increase the effect of warfarin by reducing the breakdown of warfarin include amiodarone (Cordarone), trimethoprim/sulfamethoxazole (Bactrim), fluconazole (Diflucan), itraconazole (Sporanox), fluvastatin, fluvoxamine, metronidazole miconazole, voriconazole (Vfend), zafirlukast (Accolate), ciprofloxacin (Cipro), cimetidine, atorvastatin (Lipitor), clarithromycin (Biaxin), fluoxetine (Prozac), indinavir (Crixivan), and ritonavir (Norvir).
- Drugs that may reduce the effect of warfarin by increasing its breakdown include St. John's wort, carbamazepine (Tegretol, Tegretol XR, Equetro, Carbatrol), rifampin, bosentan (Tracleer), and prednisone.
- Bleeding is increased by other anticoagulants such as heparin, argatroban (Acova), dabigatran (Pradaxa), and others; antiplatelet drugs such as aspirin and other nonsteroidal anti-inflammatory drugs (for example, ibuprofen [Motrin], naproxen [Alleve]), clopidogrel (Plavix), and prasugrel (Effient); serotonin reuptake inhibitors (SSRIs) such as fluoxetine (Prozac) and paroxetine (Paxil). Garlic and ginkgo also increase the risk of bleeding because they cause bleeding when taken alone.
- Foods with high vitamin K content (for example, green leafy vegetables) reduce the effect of warfarin. Maintenance of a consistent intake of vitamin K containing foods is important to avoid fluctuations in the effect of warfarin.
IMAGESBrowse through our medical image collection to see illustrations of human anatomy and physiology See Images
Is warfarin safe to take if I'm pregnant or breastfeeding?
What else should I know about warfarin?
What preparations of warfarin are available?
- Tablets: 1, 2, 2.5, 3, 4, 5, 6, 5, 7.5 and 10 mg.
- Powder for Injection: 5 mg/vial
How should I keep warfarin stored?
Warfarin should be stored at room temperature, 59 F to 86 F (15 C to 30 C), in tight, light resistant container.
Warfarin (Coumadin, Jantoven) is an anticoagulant drug that inhibits the blood from clotting, thus preventing blood clots. It is prescribed for the treatment of patients with deep vein thrombosis, the reduction of pulmonary embolism, and in patients with atrial fibrillation to reduce the risk of strokes and heart attack. Common side effects of warfarin include:
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