warfarin

Warfarin is an anticoagulant (blood thinner). It reduces the formation of blood clots.

Warfarin is used to prevent heart attacks, strokes, and blood clots in veins and arteries.

Warfarin may also be used for purposes not listed in this medication guide.

Important information

You should not take warfarin if you have a bleeding disorder, blood in your urine or stools, stomach bleeding, an infection of the lining of your heart, bleeding in your brain, recent or upcoming surgery, or if you need a spinal tap or epidural. Do not take warfarin if you cannot take it on time every day.

Do not use warfarin if you are pregnant, unless your doctor tells you to.

While using warfarin, you will need frequent "INR" or prothrombin time tests to measure your blood-clotting time.

Warfarin increases your risk of bleeding, which can be severe or life-threatening. Call your doctor or seek emergency medical attention if you have bleeding that will not stop, if you have black or bloody stools, or if you cough up blood or vomit that looks like coffee grounds.

Many drugs can cause serious medical problems when used with warfarin. Tell your doctor about all medicines you have recently used.

Before taking this medicine

You should not take warfarin if you are allergic to it, or if you have:

• hemophilia or any bleeding disorder that is inherited or caused by disease;

• a blood cell disorder (such as low red blood cells or low platelets);

• blood in your urine or stools, or if you have been coughing up blood;

• an infection of the lining of your heart (bacterial endocarditis);

• stomach or intestinal bleeding or ulcer;

• recent head injury, aneurysm, or bleeding in the brain; or

• if you undergo a spinal tap or spinal anesthesia (epidural).

You should not take warfarin if you cannot be reliable in taking it because of alcoholism, psychiatric problems, dementia, or similar conditions.

Warfarin can make you bleed more easily, especially if you have:

• a history of bleeding problems;

• high blood pressure or severe heart disease;

• kidney or liver disease;

• cancer;

• a disease affecting the blood vessels in your brain;

• a history of stomach or intestinal bleeding;

• a surgery or medical emergency, or if you receive any type of injection (shot);

• if you are 65 or older; or

• if you are severely ill or debilitated.

To make sure warfarin is safe for you, tell your doctor if you have:

• celiac sprue (an intestinal disorder);

• diabetes;

• congestive heart failure;

• overactive thyroid;

• recent or upcoming surgery on your brain, spine, or eye;

• a connective tissue disorder such as Marfan Syndrome, Sjogren syndrome, scleroderma, rheumatoid arthritis, or lupus;

• a hereditary clotting deficiency (warfarin may make your symptoms worse at first);

• if you use a catheter; or

• if you have ever had low blood platelets after receiving heparin.

Do not use warfarin if you are pregnant, unless your doctor tells you to. Warfarin can cause birth defects, but preventing blood clots in certain women may outweigh any risks to the baby. Use effective birth control to prevent pregnancy during treatment. Tell your doctor right away if you become pregnant.

It is not known whether warfarin passes into breast milk or if it could harm a nursing baby. Tell your doctor if you are breast-feeding a baby.

How should I take warfarin?

Take warfarin exactly as prescribed by your doctor. Follow all directions on your prescription label. Your doctor may occasionally change your dose to make sure you get the best results. Do not take warfarin in larger or smaller amounts or for longer than your doctor tells you to.

Take warfarin at the same time every day, with or without food. Never take a double dose of this medicine.

While using warfarin, you will need frequent "INR" or prothrombin time tests (to measure how long it takes your blood to clot). You may not notice any change in your symptoms, but your blood work will help your doctor determine how long to treat you with warfarin. You must remain under the care of a doctor while using this medicine.

If you have received warfarin in a hospital, call or visit your doctor 3 to 7 days after you leave the hospital. Your INR will need to be tested at that time. Do not miss any follow-up appointments.

Tell your doctor if you are sick with diarrhea, fever, chills, or flu symptoms, or if your body weight changes.

You may need to stop taking warfarin 5 to 7 days before having any surgery or dental work. Call your doctor for instructions. You may also need to stop taking warfarin for a short time if you need to take antibiotics, or if you need to have a spinal tap or spinal anesthesia (epidural).

Wear a medical alert tag or carry an ID card stating that you take warfarin. Any medical care provider who treats you should know that you are using this medicine.

Store at room temperature away from heat, moisture, and light.

Warfarin dosing information

Usual Adult Dose for Congestive Heart Failure:

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

Usual Adult Dose for Thromboembolic Stroke Prophylaxis:

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

Usual Adult Dose for Myocardial Infarction:

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of therapy is usually three months following acute myocardial infarction.

Usual Adult Dose for Prevention of Thromboembolism in Atrial Fibrillation:

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

If cardioversion is planned, anticoagulant therapy is usually initiated two to four weeks prior to cardioversion and is continued for two to four weeks following successful cardioversion. If cardioversion is not planned and this patient has complicated atrial fibrillation (atrial fibrillation associated with underlying heart disease) the duration of therapy is typically lifelong.

Usual Adult Dose for Deep Vein Thrombosis Prophylaxis after Hip Replacement Surgery:

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of anticoagulant therapy for a first-time deep venous thrombosis is usually 3 to 12 months, depending on the reversibility of the condition which may have predisposed this patient to thrombosis. For patients with a first episode of DVT secondary to a reversible risk factor, 3 months of warfarin therapy is recommended. For patients with a first episode of idiopathic DVT, at least 6 to 12 months of treatment is recommended. For patients with two or more episodes of documented DVT, indefinite treatment with warfarin is recommended. For patients with a first episode of DVT who have documented antiphospholipid antibodies or who have two or more thrombophilic conditions, treatment for 12 months is recommended and indefinite therapy is suggested. For patients with a first episode of DVT who have documented deficiency of Protein C or Protein S, deficiency of antithrombin, or the Factor V Leiden or prothrombin 20210 gene mutation, homocystinemia, or high Factor VIII levels, treatment for 6 to 12 months is recommended and indefinite therapy is suggested for idiopathic thrombosis.

Usual Adult Dose for Deep Vein Thrombosis -- First Event:

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of anticoagulant therapy for a first-time deep venous thrombosis is usually 3 to 12 months, depending on the reversibility of the condition which may have predisposed this patient to thrombosis. For patients with a first episode of DVT secondary to a reversible risk factor, 3 months of warfarin therapy is recommended. For patients with a first episode of idiopathic DVT, at least 6 to 12 months of treatment is recommended. For patients with two or more episodes of documented DVT, indefinite treatment with warfarin is recommended. For patients with a first episode of DVT who have documented antiphospholipid antibodies or who have two or more thrombophilic conditions, treatment for 12 months is recommended and indefinite therapy is suggested. For patients with a first episode of DVT who have documented deficiency of Protein C or Protein S, deficiency of antithrombin, or the Factor V Leiden or prothrombin 20210 gene mutation, homocystinemia, or high Factor VIII levels, treatment for 6 to 12 months is recommended and indefinite therapy is suggested for idiopathic thrombosis.

Usual Adult Dose for Deep Vein Thrombosis -- Recurrent Event:

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of anticoagulant therapy for a first-time deep venous thrombosis is usually 3 to 12 months, depending on the reversibility of the condition which may have predisposed this patient to thrombosis. For patients with a first episode of DVT secondary to a reversible risk factor, 3 months of warfarin therapy is recommended. For patients with a first episode of idiopathic DVT, at least 6 to 12 months of treatment is recommended. For patients with two or more episodes of documented DVT, indefinite treatment with warfarin is recommended. For patients with a first episode of DVT who have documented antiphospholipid antibodies or who have two or more thrombophilic conditions, treatment for 12 months is recommended and indefinite therapy is suggested. For patients with a first episode of DVT who have documented deficiency of Protein C or Protein S, deficiency of antithrombin, or the Factor V Leiden or prothrombin 20210 gene mutation, homocystinemia, or high Factor VIII levels, treatment for 6 to 12 months is recommended and indefinite therapy is suggested for idiopathic thrombosis.

Usual Adult Dose for Deep Vein Thrombosis Prophylaxis after Knee Replacement Surgery:

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of anticoagulant therapy for a first-time deep venous thrombosis is usually 3 to 12 months, depending on the reversibility of the condition which may have predisposed this patient to thrombosis. For patients with a first episode of DVT secondary to a reversible risk factor, 3 months of warfarin therapy is recommended. For patients with a first episode of idiopathic DVT, at least 6 to 12 months of treatment is recommended. For patients with two or more episodes of documented DVT, indefinite treatment with warfarin is recommended. For patients with a first episode of DVT who have documented antiphospholipid antibodies or who have two or more thrombophilic conditions, treatment for 12 months is recommended and indefinite therapy is suggested. For patients with a first episode of DVT who have documented deficiency of Protein C or Protein S, deficiency of antithrombin, or the Factor V Leiden or prothrombin 20210 gene mutation, homocystinemia, or high Factor VIII levels, treatment for 6 to 12 months is recommended and indefinite therapy is suggested for idiopathic thrombosis.

Usual Adult Dose for Prosthetic Heart Valves -- Tissue Valves:

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of anticoagulant therapy following tissue heart valve replacement surgery is usually 6 to 12 weeks. The duration of therapy may be longer in patients with a tissue valve in the mitral location, particularly in the presence of a large left atrium and/or atrial fibrillation. In patients who receive a mechanical heart valve, lifelong anticoagulant therapy is usually needed and low dose aspirin (80 to 100 mg/day) may be added in higher risk patients.

Usual Adult Dose for Prosthetic Heart Valves -- Mechanical Valves:

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of anticoagulant therapy following tissue heart valve replacement surgery is usually 6 to 12 weeks. The duration of therapy may be longer in patients with a tissue valve in the mitral location, particularly in the presence of a large left atrium and/or atrial fibrillation. In patients who receive a mechanical heart valve, lifelong anticoagulant therapy is usually needed and low dose aspirin (80 to 100 mg/day) may be added in higher risk patients.

Usual Adult Dose for Pulmonary Embolism -- First Event:

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of anticoagulant therapy for a first occurrence of pulmonary embolism is 3 to 12 months depending on the reversibility of the condition which may have predisposed this patient to thrombosis. For patients with a first episode of DVT or PE secondary to a reversible risk factor, 3 months of warfarin therapy is recommended. For patients with a first episode of idiopathic DVT or PE, at least 6 to 12 months of treatment is recommended. For patients with two or more episodes of documented DVT or PE, indefinite treatment with warfarin is recommended. For patients with a first episode of DVT or PE who have documented antiphospholipid antibodies or who have two or more thrombophilic conditions, treatment for 12 months is recommended and indefinite therapy is suggested. For patients with a first episode of DVT or PE who have documented deficiency of Protein C or Protein S, deficiency of antithrombin, or the Factor V Leiden or prothrombin 20210 gene mutation, homocystinemia, or high Factor VIII levels, treatment for 6 to 12 months is recommended and indefinite therapy is suggested for idiopathic thrombosis.

Usual Adult Dose for Pulmonary Embolism -- Recurrent Event:

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of anticoagulant therapy for a first occurrence of pulmonary embolism is 3 to 12 months depending on the reversibility of the condition which may have predisposed this patient to thrombosis. For patients with a first episode of DVT or PE secondary to a reversible risk factor, 3 months of warfarin therapy is recommended. For patients with a first episode of idiopathic DVT or PE, at least 6 to 12 months of treatment is recommended. For patients with two or more episodes of documented DVT or PE, indefinite treatment with warfarin is recommended. For patients with a first episode of DVT or PE who have documented antiphospholipid antibodies or who have two or more thrombophilic conditions, treatment for 12 months is recommended and indefinite therapy is suggested. For patients with a first episode of DVT or PE who have documented deficiency of Protein C or Protein S, deficiency of antithrombin, or the Factor V Leiden or prothrombin 20210 gene mutation, homocystinemia, or high Factor VIII levels, treatment for 6 to 12 months is recommended and indefinite therapy is suggested for idiopathic thrombosis.

Usual Adult Dose for Chronic Central Venous Catheterization:

1 mg orally or intravenously once a day

Therapy should be initiated three days before insertion of the catheter. No changes in coagulation values are expected with this low dose.

What happens if I miss a dose?

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. Overdose can cause excessive bleeding.

What should I avoid while taking warfarin?

Avoid activities that may increase your risk of bleeding or injury. Use extra care to prevent bleeding while shaving or brushing your teeth. You may still bleed more easily for several days after you stop taking warfarin.

Ask your doctor before taking any medicine for pain, arthritis, fever, or swelling. This includes acetaminophen (Tylenol), aspirin, ibuprofen (Advil, Motrin), naproxen (Aleve), celecoxib (Celebrex), diclofenac, indomethacin, meloxicam, and others. These medicines may affect blood clotting and may also increase your risk of stomach bleeding.

Avoid making any changes in your diet without first talking to your doctor. Foods that are high in vitamin K (liver, leafy green vegetables, or vegetable oils) can make warfarin less effective. If these foods are part of your diet, eat a consistent amount on a weekly basis.

Grapefruit juice may interact with warfarin and lead to unwanted side effects. Avoid the use of grapefruit products while taking this medicine.

Warfarin side effects

Get emergency medical help if you have any of these signs of an allergic reaction to warfarin: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Warfarin may cause you to bleed more easily, which can be severe or life-threatening. Seek emergency medical attention if you have any unusual bleeding, or bleeding that will not stop. You may also have bleeding on the inside of your body, such as in your stomach or intestines. Call your doctor at once if you have black or bloody stools, or if you cough up blood or vomit that looks like coffee grounds. These could be signs of bleeding in your digestive tract.

Also call your doctor at once if you have:

• pain, swelling, hot or cold feeling, skin changes, or discoloration anywhere on your body;

• sudden and severe leg or foot pain, foot ulcer, purple toes or fingers;

• sudden headache, dizziness, or weakness;

• easy bruising, purple or red pinpoint spots under your skin, bleeding from wounds or needle injections;

• pale skin, feeling light-headed or short of breath, rapid heart rate, trouble concentrating;

• dark urine, jaundice (yellowing of the skin or eyes);

• little or no urinating;

• numbness or muscle weakness; or

• pain in your stomach, back, or sides.

Common warfarin side effects may include:

• nausea, vomiting, mild stomach pain;

• bloating, gas; or

• altered sense of taste.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

See also: Side effects (in more detail)

What other drugs will affect warfarin?

Many drugs (including some over-the-counter medicines and herbal products) can affect your INR and may increase the risk of bleeding if you take them with warfarin. Not all possible drug interactions are listed in this medication guide. It is very important to ask your doctor before you start or stop using any other medicine, especially:

• other medicines to prevent blood clots;

• medicine to treat any type of infection, including tuberculosis;

• supplements that contain vitamin K;

• an antidepressant--citalopram, duloxetine, fluoxetine, fluvoxamine, paroxetine, sertraline, venlafaxine, vilazodone, and others; seizure medicine--carbamazepine, phenobarbital, phenytoin; herbal (botanical) products--coenzyme Q10, cranberry, echinacea, garlic, ginkgo biloba, ginseng, goldenseal, or St. John"s wort.

This list is not complete and many other drugs can interact with warfarin. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Give a list of all your medicines to any healthcare provider who treats you.