Warfarin can cause major or fatal bleeding. Regular monitoring of INR should be performed on all treated patients. Drugs, dietary changes, and other factors affect INR levels achieved with warfarin sodium therapy. Instruct patients about prevention measures to minimize risk of bleeding and to report signs and symptoms of bleeding .
Medically reviewed on Oct 4, 2018
Commonly used brand name(s)
In the U.S.
Available Dosage Forms:
Therapeutic Class: Anticoagulant
Chemical Class: Coumarin (class)
Uses For warfarin
Warfarin is used to prevent or treat blood clots, including deep venous thrombosis or pulmonary embolism. It is also used for blood clots that may be caused by certain heart conditions, open-heart surgery, or after a heart attack. Warfarin is an anticoagulant (blood thinner) that decreases the clotting ability of the blood.
Warfarin is available only with your doctor's prescription.
Before Using warfarin
In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For warfarin, the following should be considered:
Tell your doctor if you have ever had any unusual or allergic reaction to warfarin or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.
Appropriate studies have not been performed on the relationship of age to the effects of warfarin in the pediatric population. Safety and efficacy have not been established.
Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of warfarin in the elderly. However, elderly patients may require caution and an adjustment in the dose, especially those who are at risk of bleeding.
Studies in women suggest that this medication poses minimal risk to the infant when used during breastfeeding.
Interactions with Medicines
Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking warfarin, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using warfarin with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.
Using warfarin with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Alipogene Tiparvovec
- Alteplase, Recombinant
- Amtolmetin Guacil
- Ceftaroline Fosamil
- Choline Salicylate
- Collagenase, Clostridium histolyticum
- Dabigatran Etexilate
- Doxorubicin Hydrochloride Liposome
- Drotrecogin Alfa
- Fenofibric Acid
- Fish Oil
- Flufenamic Acid
- Influenza Virus Vaccine
- Mefenamic Acid
- Methyl Salicylate
- Nalidixic Acid
- Niflumic Acid
- Nimesulide Beta Cyclodextrin
- Obeticholic Acid
- Peginterferon Alfa-2b
- Penicillin G
- Penicillin V
- Pentosan Polysulfate Sodium
- Reteplase, Recombinant
- St John's Wort
- Tiaprofenic Acid
- Tolfenamic Acid
- Valproic Acid
- Vincristine Sulfate Liposome
Using warfarin with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Bee Pollen
- Chloral Hydrate
- Choline Magnesium Trisalicylate
- Coenzyme Q10
- Dong Quai
- Eslicarbazepine Acetate
- Estradiol Cypionate
- Estradiol Valerate
- Ethinyl Estradiol
- Ethynodiol Diacetate
- Medroxyprogesterone Acetate
- Potassium Iodide
- Salicylic Acid
- Sodium Salicylate
- Sodium Thiosalicylate
- Trolamine Salicylate
- Vitamin A
- Vitamin E
Interactions with Food/Tobacco/Alcohol
Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using warfarin with any of the following is usually not recommended, but may be unavoidable in some cases. If used together, your doctor may change the dose or how often you use warfarin, or give you special instructions about the use of food, alcohol, or tobacco.
- Cranberry Juice
Using warfarin with any of the following may cause an increased risk of certain side effects but may be unavoidable in some cases. If used together, your doctor may change the dose or how often you use warfarin, or give you special instructions about the use of food, alcohol, or tobacco.
- Black Tea
- Enteral Nutrition
- Green Tea
- High Protein Food
- Noni Juice
- Vitamin K Containing Food
Other Medical Problems
The presence of other medical problems may affect the use of warfarin. Make sure you tell your doctor if you have any other medical problems, especially:
- Anemia or
- Catheter insertion or
- Congestive heart failure or
- Deep venous thrombosis, heparin-induced or
- Diabetes or
- Falls or blows to the body or head or
- Hypertension (high blood pressure) or
- Infection or
- Kidney disease, or history of or
- Major surgery, any type or
- Polycythemia vera (blood disease) or
- Protein C deficiency (rare hereditary disease), known or suspected or
- Stomach or bowel problems, including bleeding or
- Thrombocytopenia, heparin-induced or
- Trauma or
- Vasculitis (inflammation of blood vessel)—Use with caution. May cause side effects to become worse.
- Blood disease or bleeding problems or
- Heart infection or
- High blood pressure (high blood pressure), severe or
- Spinal anesthesia, recent or
- Stomach or intestinal ulcer, active or
- Stroke, history of or
- Surgery, recent or scheduled (eg, surgery of the eye, brain, or spine) or
- Threatened miscarriage—Should not be used in patients with these conditions. The risk of bleeding from warfarin may be increased.
- Diarrhea or
- Liver disease or
- Malnutrition or
- Steatorrhea (fats in the stool) or
- Vitamin K deficiency—Use with caution. May increase risk of bleeding.
Proper Use of warfarin
Take warfarin only as directed by your doctor. Your dose may need to be changed several times in order to find out what works best for you. Do not use more of it, do not use it more often, and do not use it for a longer time than your doctor ordered.
Warfarin should come with a Medication Guide. Read and follow these instructions carefully. Ask your doctor if you have any questions.
Carefully follow your doctor's instructions about any special diet. Warfarin works best when you eat about the same amount of vitamin K in your food every day. Tell your doctor before changing your diet. Avoid big changes in how much vitamin K you eat. Some foods that have a high amount of vitamin K are asparagus, broccoli, brussels sprouts, cabbage, green leafy vegetables (such as collards, turnip greens, mustard greens, spinach, and salad greens), plums, rhubarb, and certain vegetable oils (such as soybean oil and canola oil).
You may take the tablets on a full or empty stomach.
Do not drink grapefruit juice while you are using warfarin. Grapefruit juice may change the amount of warfarin that is absorbed in the body.
The dose of warfarin will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of warfarin. If your dose is different, do not change it unless your doctor tells you to do so.
The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.
- For oral dosage form (tablets):
- For prevention or treatment of blood clots:
- Adult—At first, 2 to 5 milligrams (mg) as a single dose once per day. Your doctor may adjust your dose if needed. However, the dose is usually not more than 10 mg per day.
- Children—Use and dose must be determined by your doctor.
- For prevention or treatment of blood clots:
If you miss a dose of warfarin, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.
Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.
Keep out of the reach of children.
Do not keep outdated medicine or medicine no longer needed.
Ask your healthcare professional how you should dispose of any medicine you do not use.
Precautions While Using warfarin
It is very important that your doctor check your progress at regular visits to make sure warfarin is working properly. Blood tests, such as an INR, are needed to check for proper dosage and unwanted side effects. Be sure to keep all appointments.
Using warfarin while you are pregnant can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant during treatment and for at least 1 month after the last dose. If you think you have become pregnant while using warfarin, tell your doctor right away.
Make sure any doctor or dentist who treats you knows that you are using warfarin. You may need to stop using warfarin several days before having surgery or medical tests.
Check with your doctor immediately if you have diarrhea, fever, or any symptoms of an infection.
Warfarin may cause skin necrosis or gangrene. Call your doctor right away if you have pain, a color change, or a temperature change to any area of your body. Call your doctor right away if you have pain in your toes and they look purple or dark in color. These could be signs of a serious medical problem.
Calciphylaxis or calcium uremic arteriolopathy may occur in patients with or without end-stage kidney disease. Tell your doctor right away if you have purplish red, net-like, blotchy spots on the skin.
Warfarin may increase your risk of having kidney problems, including acute kidney injury. Check with your doctor right away if you have blood in the urine, decreased urine output, muscle twitching, nausea, rapid weight gain, seizures, stupor, swelling of the face, ankles, or hands, or unusual tiredness or weakness.
Warfarin may increase your chance of bleeding. Check with your doctor right away if you notice any unusual bleeding or bruising, black, tarry stools, blood in the urine or stools, or pinpoint red spots on your skin. Avoid picking your nose. If you need to blow your nose, blow it gently.
Be careful when using a regular toothbrush, dental floss, or toothpick. Your medical doctor, dentist, or nurse may recommend other ways to clean your teeth and gums. Check with your medical doctor before having any dental work done.
Be careful not to cut yourself when you are using sharp objects, such as a safety razor or fingernail or toenail cutters. Avoid contact sports or other situations where bruising or injury could occur.
It is recommended that you carry identification that says you are using warfarin. If you have any questions about what kind of identification to carry, check with your doctor.
Do not take other medicines unless they have been discussed with your doctor. This includes prescription medicines, nonprescription (over-the-counter [OTC]) medicines, and herbal or vitamin supplements.
Warfarin Side Effects
Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.
Check with your doctor immediately if any of the following side effects occur:
- Bleeding gums
- blood in the urine
- bloody stools
- blurred vision
- burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
- chest pain or discomfort
- coughing up blood
- difficulty with breathing or swallowing
- dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
- excessive bruising
- increased menstrual flow or vaginal bleeding
- peeling of the skin
- prolonged bleeding from cuts
- red or black, tarry stools
- red or dark brown urine
- stomach pain with cramping
- unexplained swelling
- unusual tiredness or weakness
- Arm, back, or jaw pain
- blue-green to black skin discoloration
- blue or purple toes
- change in consciousness
- chest tightness or heaviness
- clay-colored stools
- fainting or loss of consciousness
- fast or irregular breathing
- fast or irregular heartbeat
- itching or skin rash
- light-colored stools
- loss of appetite
- nausea and vomiting
- pain in the toes
- pain, redness, or sloughing of the skin
- pale skin
- purplish red, net-like, blotchy spots on the skin
- skin blisters
- small red or purple spots on the skin
- stomach pain
- swelling of the eyes or eyelids
- troubled breathing with exertion
- unpleasant breath odor
- unusual bleeding or bruising
- upper right stomach pain
- vomiting of blood
- yellow eyes and skin
Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:
- Joint pain
- muscle pain
- change in taste, or bad, unusual, or unpleasant (after) taste
- cold intolerance
- excess air or gas in the stomach or intestines
- full feeling
- general feeling of discomfort or illness
- hair loss or thinning of the hair
- hives or welts
- lack or loss of strength
- passing gas
- red, sore, or itching skin
- sores, welting, or blisters
- unusual drowsiness, dullness, or feeling of sluggishness
Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.
Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.
See also: Side effects (in more detail)
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
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