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Warfarin (Coumadin)

Article Translations: (Spanish)

How does this medicine work?

Warfarin (war-far-in) is an anticoagulant, also known as a "blood thinner". Warfarin helps prevent blood clots from forming in the blood vessels. It is prescribed to patients to treat a blood clot or prevent formation of a blood clot in high risk settings. Warfarin does not dissolve clots but it prevents blood clots from forming and allows your body to break up the clot more easily on its own. In order for this medicine to safely help your child, it must be given correctly.

The most common brand of warfarin is Coumadin. Discuss with your provider before you switch brands of warfarin because different brands may not produce the same effect in your child's body. 

How should I give it?

  • Warfarin comes in tablet form. There are many strengths of warfarin tablets. These are color coded based on the strength of the warfarin tablet. Read the label and check to be sure that you are giving the correct dose.
  • Give the exact dose of warfarin that the provider prescribed at the same time each day. It is helpful to keep a warfarin calendar with the doses marked on each day, and check them off when they are given.
  • For children who cannot swallow pills, ask the pharmacist how to give it.

Are there any precautions about food or other medicines?

  • This medicine can be given with or without food. Avoid alcohol or foods/medicines containing alcohol.
  • Vitamin K decreases the effect of warfarin. Foods high in vitamin K include green leafy vegetables, cauliflower, egg yolks, liver, and soybean products. A change in the diet's intake of vitamin K foods can impact the dose the child needs. It is important to keep a consistent diet. If there are large changes in lab results, a diary of the food intake could help find a possible dietary cause for the fluctuations. 
  • Do not make major changes in your child's eating habits or give vitamins, herbal products, or nutrition supplements without checking with the provider.
  • Do not use any medicine (prescription or non-prescription) while taking warfarin without checking with the pharmacist or provider. Many medicines, such as antibiotics, birth control pills, aspirin, vitamins, antacids, laxatives, and nutrition supplements, can change the effect of warfarin in the body.

What should I do if a dose is missed?

If a dose is missed, give it as soon as you remember that day. If you do not remember if you have given a dose, do not give it. Go back to the regular schedule tomorrow. If you do not remember until the next day, continue with the regular schedule and do not give the missed dose. If in doubt, it is generally safer to take too little than too much warfarin.

If your child throws up within 30 minutes after receiving a dose, give it again. If your child vomits the second dose, do not repeat it again. If more than one dose is missed or vomited, call the clinic.

What are the side effects?

The main side effect of warfarin is bleeding. This is why it must be monitored carefully. Have your child's blood tests done regularly, as directed by the provider.

* Ways to prevent bleeding are:

  • Brush teeth gently with a soft toothbrush.
  • Floss teeth gently after brushing (for children younger than 9 years, parents should help with brushing and flossing).
  • Cut fingernails and toenails carefully.
  • Prevent constipation by drinking extra fluids and eating high-fiber foods.
  • Use an electric razor rather than a razor blade.

Other side effects include upset stomach and vomiting.

When should I call the Provider?

  • if 2 or more doses are missed
  • any new medical problems
  • any unexplained changes in body functions such as urinating or stools (bowel movements)
  • a major change in diet is planned
  • unable to eat for several days
  • temperature higher than 101° F for more than 2 days
  • diarrhea
  • vision changes
  • becomes pregnant
  • bleeding from a cut that will not stop after 5 minutes of pressure
  • bleeding from the mouth or nose
  • coughing up blood
  • other signs of bleeding:
    • swelling, tenderness, or redness in a joint, especially after an injury
    • increased menstrual flow
    • increased bruising
    • black stools
    • stools with red streaks
  • severe, prolonged headache
  • unusual stomach or back pain
  • weakness, dizziness, feeling faint
  • signs of allergic reaction
    • rash or hives
    • wheezing
    • trouble breathing - call 911

What else do I need to know?

  • It may take a few weeks to see the full effect.
  • Carry an ID card or wear a medical alert bracelet/necklace to let emergency caregivers know that your child is on warfarin.
  • While your child is taking warfarin, tests called prothrombin time (PT) or International Normalized Ratio (INR) must be done on a regular basis to check how well your child's blood is clotting. The tests are done more often at first, and less often after your child's dose has been established. These tests are needed to make warfarin therapy safe. It is very important to keep appointments with the lab for these tests so the provider can adjust the warfarin dose as needed.
  • If your pharmacist changes the warfarin brand or dose schedule, call the clinic about the change.
  • Be sure to see the dentist regularly.

What else do I need to know?

  • You and your child should know the names of all the medicines he or she is taking. Be sure to tell anyone involved (dentists, surgeons, others) in your child's care that he or she is taking warfarin. Bring the medicine container when your child comes to the clinic or emergency department.
  • Always make sure you have enough warfarin on hand. Each time you refill the prescription, check to see how many refills are left. If no refills are left, the pharmacy will need 2 or 3 days to contact the clinic to renew the prescription.
  • Before giving the first dose, read the label. Be sure it is what was prescribed. After a refill, if the medicine looks different to you, ask your pharmacist about it before giving it.
  • Check the label for the expiration date.
  • Store all medicines in their original containers and away from direct sunlight or heat. Do not store in humid places such as the bathroom. Keep all medicines out of children's reach, locked up if possible.
  • If too much or the wrong kind of medicine is taken, call the Poison Control Center right away (1-800-222-1222), or go to the nearest emergency room for treatment.
  • If your child is unconscious or has a seizure, call 911.


This sheet is not specific to your child, but provides general information. If you have any questions, please call the clinic or pharmacy.

Children's Hospitals and Clinics of Minnesota
Patient/Family Education
2525 Chicago Avenue South
Minneapolis, MN 55404
Last reviewed 1/2019 ©Copyright

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This page is not specific to your child, but provides general information on the topic above. If you have any questions, please call your clinic. For more reading material about this and other health topics, please call or visit Children's Minnesota Family Resource Center library, or visit

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