Your child needs to take the medicine called warfarin (say: WAR-far-in). This information sheet explains what warfarin does and how to give it to your child. It also explains what side effects or problems your child may have when they take this medicine.
What is warfarin?
Warfarin is a medicine called an anticoagulant (blood thinner). Warfarin is used to stop the blood from clotting too easily. It prevents harmful clots from forming and getting bigger in the blood. It does this by blocking the action of vitamin K, which is used to help the blood to clot.
You may hear warfarin called by its brand name, Coumadin. Warfarin comes in a tablet form. It is available in different strengths, which are colour-coded.
Before giving warfarin to your child
Tell your child's doctor if your child:
- has ever reacted badly to warfarin or any other medicine, preservative or colouring agent
- has recently had or will be having procedures that can increase the risk of bleeding (e.g., surgery)
- has any other conditions that increase the risk of bleeding, or has any active bleeding
- has very high blood pressure
- may be pregnant
Talk with your child's doctor or pharmacist if your child has any of the following conditions. Precautions may need to be taken with this medicine if your child has:
- kidney or liver problems
- diabetes
- heart disease
There are some medicines that should not be taken together with warfarin or in some cases the dose of warfarin or the other medicine may need to be adjusted.
It is important that you tell your doctor and pharmacist if your child takes any other medications (prescription, over the counter or herbal) including:
- medicines used for pain or fever: Non-Steroid Anti-Inflammatory Drugs (NSAIDs) such as ASA (Aspirin) and ibuprofen (Motrin, Advil) usually cannot be given while on warfarin as they may increase the risk of bleeding. Some cold and flu medicines contain ASA or ibuprofen too. Check with your pharmacist or doctor first.
- any other medicines that can affect blood clotting, such as heparin, enoxaparin (Lovenox) or tinzaparin (Innohep)
- antibiotics such as ciprofloxacin (Cipro), erythromycin (Eryc) and trimethoprim-sulfamethoxazole (Septra)
- herbals including: cranberry juice/products, St. John's Wort, ginseng, garlic, coenzyme Q10
How should you give your child warfarin?
Follow these instructions when giving your child warfarin:
- give your child warfarin exactly as the doctor or pharmacist tells you to
- give your child this medicine at the same times each day
- warfarin can be taken with or without food
- give warfarin with food if it causes an upset stomach
- if your child has difficulty swallowing tablets, dissolve the tablets in a small amount of fluid such as water or juice, or you may crush the tablets and mix it in a spoonful of applesauce or pudding.
What should you do if your child misses a dose of warfarin?
If your child misses a dose of this medicine:
- give the missed dose as soon as you remember.
- if it is almost time for the next dose, skip the missed dose. Give the next dose at the regular time.
- do not give two doses to make up for one missed dose.
- never give more than one dose a day.
How long does warfarin take to work?
Warfarin begins to work within 24 hours after first taking it but the full effect may take 3 to 4 days to occur.
What are the possible side effects of warfarin?
Your child may have some of these side effects while they take warfarin. Check with your child's doctor if your child continues to have any of these side effects, if they do not go away, or if they bother your child:
- bleeding or bruising more easily than normal e.g. increased bleeding from cuts, bleeding from the gums when brushing teeth; bruising or purplish areas on the skin; nosebleeds; for older girls, longer or heavier menstrual periods.
- headache
Most of the following side effects are not common, but they may be a sign of a serious problem. Call the Thrombosis Team or your child's doctor right away, or take your child to Emergency if your child has any of these side effects:
- unusual or severe bleeding, e.g., a very long nosebleed, blood in the urine or stools (red/dark urine, red/black tarry stools), coughing or throwing up blood or material that looks like coffee grounds, bleeding from cuts and wounds that does not stop
- dizziness, lightheadedness or fainting
- severe stomach pain
- swelling in hands, ankles or feet
- numbness, tingling or weakness anywhere in the body, or problems with movement, swallowing or speech
- signs of a life-threatening reaction, including wheezing; shortness of breath, chest tightness or chest pain; fever; itching; bad cough; blue skin colour; swelling of face, lips, tongue or throat
- purple discoloration of the toes or the soles of the feet, or new pain in a leg, foot or toes
What safety measures should you take when your child is using warfarin?
Before starting treatment with warfarin, inform the doctor if your child has problems with coordination as falling often may increase the risk of bleeding. During warfarin treatment, talk to the doctor immediately if your child has a bad fall, especially if your child hit their head.
Contact sports are not recommended, such as hockey or football. They may get bruised and bleed more easily from injuries. Head protection is important for sports, such as bicycling or skateboarding.
Before your child has any kind of surgery (including dental work), medical procedure or emergency treatment, tell the doctor or dentist that your child is taking warfarin. If your child is followed by the Thrombosis Service, please call them in advance. It may be necessary to stop giving this medicine temporarily to prevent bleeding from the surgery or procedure.
Inform your child's doctor before your child gets a vaccine by needle. Needles into the muscle may cause bleeding in patients taking this medicine.
Vitamin K can reverse the effects of warfarin and can be found in various multivitamins, dietary supplements and foods. Foods that have large amounts of vitamin K are dark green, leafy vegetables (alfalfa, asparagus, broccoli, brussel sprouts, collard greens, cabbage, cauliflower, kale, lettuce, spinach and water cress), green tea, liver and some vegetable oils. Foods rich in vitamin K do not need to be avoided, but make sure the amount of these foods your child eats is similar from day to day.
Inform your child's doctor if your child develops an illness including symptoms of diarrhea, vomiting or fever or has a change in eating habits as the doctor may want to adjust the dose of warfarin.
For older boys and girls, alcohol use should be avoided during warfarin treatment. Excessive alcohol use can increase the risk of bleeding with warfarin.
There is a chance that warfarin may cause birth defects if it is taken at the time of conception or if it is taken during pregnancy. If your child is sexually active it is best that she use some kind of birth control while receiving warfarin. Tell the doctor right away if your child may be pregnant.
It may be recommended that your child wear a Medic Alert bracelet or necklace while taking warfarin. The Thrombosis Team will tell you if this is needed depending on how long your child will be on warfarin.
How much of warfarin does my child need?
How much warfarin your child needs will depend on how their body responds to the medicine. The dose is changed according to the results of bloodwork, called INR. Follow your doctor's instructions for the right amount of warfarin to give
What other important information should I know about warfarin?
- When starting warfarin treatment, your child will need routine bloodwork (INR tests) to determine if the dose needs to be changed. The INR test is used to determine how much warfarin your child needs. Keep all appointments at the clinic or doctor's office and for blood tests, so that your child's response to warfarin can be checked. It may be helpful for you to use a calendar to keep track of how much warfarin is taken each day, changes in doses, and blood test appointments.
- Keep a list of all medications your child is taking and show the list to the doctor and pharmacist. Also, inform them if there are ever any changes or additions to your child's medications or diet.
- Do not share your child's medicine with others and do not give anyone else's medicine to your child.
- Make sure you always have enough warfarin to last through weekends, holidays and vacations. Call your pharmacy at least 2 days before your child runs out of medicine to order refills.
- Keep warfarin at room temperature in a cool, dry place away from sunlight. Do NOT store it in the bathroom or kitchen.
- Do not keep any medicines that are out of date. Check with your pharmacist about the best way to throw away outdated or leftover medicines.
Keep warfarin out of your child’s sight and reach and locked up in a safe place. If your child takes too much warfarin, call your local Poison Information Centre at one of these numbers. These calls are free.
- Call 1-844 POISON-X, or 1-844-764-7669, from anywhere in Canada except Quebec.
- Call 1-800-463-5060 if you live in Quebec.
