warfarin, Coumadin, Jantoven

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Medical Author:

Omudhome Ogbru, PharmD

Omudhome Ogbru, PharmD

Dr. Ogbru received his Doctorate in Pharmacy from the University of the Pacific School of Pharmacy in 1995. He completed a Pharmacy Practice Residency at the University of Arizona/University Medical Center in 1996. He was a Professor of Pharmacy Practice and a Regional Clerkship Coordinator for the University of the Pacific School of Pharmacy from 1996-99.

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Medical Editor:

Jay W. Marks, MD

Jay W. Marks, MD

Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

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GENERIC NAME: warfarin

BRAND NAME: Coumadin, Jantoven

DRUG CLASS AND MECHANISM: 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.

PRESCRIPTION: Yes

GENERIC AVAILABLE: Yes

PREPARATIONS: Tablets: 1, 2, 2.5, 3, 4, 5, 6, 5, 7.5 and 10 mg. Powder for Injection: 5 mg/vial

STORAGE: Warfarin should be stored at room temperature, 59 F to 86 F (15 C to 30 C), in tight, light resistant container.

PRESCRIBED FOR: 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.

DOSING: 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.

DRUG INTERACTIONS: 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. Following are a few examples of drugs that interact with warfarin. Drugs the 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).

Report Problems to the Food and Drug Administration You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088. Need help identifying pills and medications? Use the pill identifier tool on RxList.