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

Coumadin is used to treat or prevent blood clots in veins or arteries, which can reduce the risk of stroke, heart attack, or other serious conditions.

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

Warnings

You should not take Coumadin if you are prone to bleeding because of a medical condition, if you have an upcoming surgery, or if you need a spinal tap or epidural. Talk to your doctor if you think you will not be able to take Coumadin on time every day.

Warfarin increases your risk of severe or fatal bleeding, especially if you have certain medical conditions, if you are 65 or older, or if you have had a stroke, or bleeding in your stomach or intestines. Seek emergency help if you have any bleeding that will not stop.

Call your doctor at once if you have other signs of bleeding such as: swelling, pain, feeling very weak or dizzy, unusual bruising, bleeding gums, nosebleeds, heavy menstrual periods or abnormal vaginal bleeding, blood in your urine, bloody or tarry stools, coughing up blood or vomit that looks like coffee grounds.

Many other drugs can increase your risk of bleeding when used with Coumadin. Tell your doctor about all medicines you have recently used.

Avoid making any changes in your diet without first talking to your doctor. Some foods can make warfarin less effective.

Before taking this medicine

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

• you have malignant hypertension, which is a specific type of very high blood pressure that comes on suddenly and quickly;
• you recently had or will have surgery on your brain, spine, or eye;
• you undergo a spinal tap or spinal anesthesia (epidural); or
• if you think you will not be able to take Coumadin on time every day, talk to your prescriber about other treatment options.

You also should not take Coumadin if you are are prone to bleeding because of a medical condition, such as:

• a blood cell disorder (such as low red blood cells or low platelets);
• ulcers or bleeding in your stomach, intestines, lungs, or urinary tract;
• an aneurysm or bleeding in the brain; or
• an infection of the lining of your heart.

Do not take Coumadin if you are pregnant, unless your doctor tells you to. Warfarin can cause birth defects, but preventing blood clots may outweigh any risks to the baby. If you are not pregnant, use effective birth control to prevent pregnancy while taking warfarin and for at least 1 month after your last dose. Tell your doctor right away if you become pregnant.

Coumadin can make you bleed more easily, especially if you have ever had:

• high blood pressure or serious heart disease;
• kidney disease;
• cancer or low blood cell counts;
• an accident or surgery;
• bleeding in your stomach or intestines;
• a stroke; or
• if you are 65 or older.

To make sure this medicine is safe for you, tell your doctor if you have ever had:

• diabetes;
• congestive heart failure;
• liver disease, kidney disease (or if you are on dialysis);
• a hereditary clotting deficiency; or
• low blood platelets after receiving heparin.

It is not known whether warfarin passes into breast milk. Watch for signs of bruising or bleeding in the baby if you take Coumadin while you are breast-feeding a baby.

How should I take Coumadin?

Take Coumadin exactly as prescribed by your doctor. Follow all directions on your prescription label. Your doctor may change your dose based on your blood tests. Do not take warfarin in larger or smaller amounts or for longer than your doctor tells you to.

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

Coumadin can make it easier for you to bleed. Seek emergency help if you have any bleeding that will not stop.

You will need frequent “INR” or prothrombin time tests (to measure your blood-clotting time and determine your warfarin dose). You must remain under the care of a doctor while taking Coumadin.

If you receive Coumadin 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 Coumadin 5 to 7 days before having any surgery, dental work, or a medical procedure. Call your doctor for instructions.

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 taking this medicine.

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

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 to avoid

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 Coumadin.

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, cranberry juice, noni juice, and pomegranate juice may interact with warfarin and lead to unwanted side effects. Avoid the use of these juice products while taking Coumadin.

Avoid drinking alcohol.

Ask your doctor before using any medicine for pain, arthritis, fever, or swelling. This includes 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.

Coumadin side effects

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

Coumadin increases your risk of bleeding, which can be severe or life-threatening. Call your doctor at once if you have any signs of bleeding such as:

• sudden headache, feeling very weak or dizzy;
• swelling, pain, unusual bruising;
• bleeding gums, nosebleeds;
• bleeding from wounds or needle injections that will not stop;
• heavy menstrual periods or abnormal vaginal bleeding;
• blood in your urine, bloody or tarry stools; or
• coughing up blood or vomit that looks like coffee grounds.

Clots formed by Coumadin may block normal blood flow, which could lead to tissue death or amputation of the affected body part. Get medical help at once if you have:

• pain, swelling, hot or cold feeling, skin changes, or discoloration anywhere on your body; or
• sudden and severe leg or foot pain, foot ulcer, purple toes or fingers.

What other drugs will affect Coumadin?

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 Coumadin. Not all possible drug interactions are listed in this medication guide. It is very important to ask your doctor and pharmacist before you start or stop using any other medicine, especially:

• other medicines to prevent blood clots;
• an antibiotic or antifungal medicine;
• supplements that contain vitamin K; or
• herbal (botanical) products – coenzyme Q10, cranberry, echinacea, garlic, ginkgo biloba, ginseng, goldenseal, or St. John’s wort.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guidelines for Pharmacogenetics-guided Warfarin Dosing: 2016 Update(December 2016) 

Updates since publication:

No updates on dosing recommendations since this publication.

Figures provided in the main manuscript of the guideline:

Supplement to: Clinical Pharmacogenetics Implementation Consortium (CPIC) Guidelines for Pharmacogenetics-guided Warfarin Dosing: 2016 Update

Tables provided in the guideline publication supplement or referenced in the guideline^a:

^aSome of the tables included in the guideline may have been updated on-line, particularly to reflect newly described or newly characterized alleles. These include the gene-specific information tables (https://www.pharmgkb.org/page/pgxGeneRef) that support CPIC guidelines by providing information regarding star (*) allele definitions, allele function, allele frequency by major ethnic groups, translations of diplotype to phenotype, and gene resource mappings.

^bBecause this guideline’s recommendations are based on genotype and not phenotype, the diplotype-phenotype tables were not created for these genes.

Original publication (October 2011):

November 2013 update to 2011 guideline:
CPIC guideline authors are aware of several recently published studies on warfarin pharmacogenetics [Articles:24251361, 24251363, 24251360]. These papers have prompted several opinion pieces [Articles:24328463, 24251364]. The authors are evaluating the information, which will be incorporated into the next update of the CPIC guideline on warfarin.

• Clinical Pharmacogenetics Implementation Consortium Guidelines for CYP2C9 and VKORC1 Genotypes and Warfarin Dosing
• 2011 supplement
• IWPC Pharmacogenetic Dosing Algorithm

This guideline has been endorsed by the American Society of Health-System Pharmacists (ASHP).