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Warfarin and INRs for cardiac patients fact sheet

Warfarin and INRs for cardiac patients

Warfarin (Marevan ®) is an anticoagulant. Anticoagulants are medications prescribed specifically to prevent and treat the formation of clots within blood vessels, also called thrombosis.

There are several reasons why children may need to take Warfarin; these include cardiomyopathy, arrhythmias, some cyanotic lesions, but most commonly, the replacement of a heart valve with a mechanical valve.

Warfarin treatment is monitored by the International Normalized Ratio (INR).  Warfarin comes in tablet form (1mg, 3mg, or 5mg) and is taken orally. You will be prescribed bottles of all three doses as your child’s doses will change regularly.

NOTE: This medicine is a long-term medication and it is very important that your child keeps taking it as stopping, in some cases, could be life threatening.

INR machines

Point of care testing machines

If your child has a mechanical valve, you may automatically be eligible for a free Coaguchek® machine for home use. While the machine is free, there is an ongoing cost to families to supply the strips that enable the machine to work. This machine is similar to a blood sugar machine and uses a small drop of blood from a finger prick to get an INR reading. It is then your responsibility to notify QPCS of the INR in order to receive any changes to the Warfarin dose.

Your Care Coordinator and your Cardiologist will help to decide if this is a good monitoring option for your child.

INR testing through a pathology service

A free INR monitoring service can be accessed through local pathology services in the community. This involves having a blood test at a pathology centre and the service then adjusts the dose of warfarin according to the INR result.

Your Care Coordinator and your Cardiologist will help to decide if this is a good monitoring option for your child.

Warfarin instructions

Your child will be given a desired INR range on discharge. Your child will commence taking Warfarin while still in hospital and once your child is within range, they will be discharged.

INRs are managed on a Monday to Friday basis between the hours of noon to 6pm. On occasions, you will be asked to ring during the weekend if testing is needed more frequently.

When you ring the 10b (cardiac ward), make sure you know your child’s INR reading, the current dose they are on, and how long they have been on this dose for. You will then be instructed by the cardiac registrar or cardiac fellow as to a new dose of Warfarin, and when to recheck your child’s INR.

Possible side effects of medication

  • bleeding
  • bruising
  • nausea
  • headache
  • light headedness or dizziness.

If your child misses a dose

For any medication information related to your child’s dosing schedule and/or missed doses, contact Ward 10b at Queensland Children’s Hospital on 3068 1627.

Things to know about taking Warfarin

  • It is very important that your child takes their dose of Warfarin each day and you keep a record of your child’s INR and dose.
  • Tell your child’s dentist or GP at the beginning of each visit if they are taking Warfarin.
  • Ensure that you store Warfarin securely and out of reach of children.
  • Do not give any other medicine, prescription or over-the-counter, without first talking to your child’s doctor or pharmacist about any interactions with Warfarin.
  • Do not use after the expiration date on the bottle.
  • Do not change the brand of Warfarin. QPCS uses the “Marevan®” brand of Warfarin. Do not use the brand “Comadin®” as it could affect your child’s INR.
  • If too much medication is given by accident, call the Cardiac ward immediately on 3068 1627.

Vitamin K and Warfarin

Eating food that contains vitamin K may make Warfarin less effective in preventing blood clots.

These foods are high in vitamin K: Broccoli, brussels sprouts, cabbage, chickpeas, green tea, lettuce, liver, spinach, and turnip greens.

These foods have a moderate amount of vitamin K: Asparagus, avocado, cauliflower, cheese, coffee, and peas.

These foods have little vitamin K: Bacon, beef, bread, butter, capsicum, carrots, celery, chicken, corn, eggs, green beans, onions, peanuts, potatoes, pork, pumpkin, rice, and tomatoes.

Call your child’s doctor if you observe any of the following:

  • Bruises or tender swellings without obvious cause
  • Severe and prolonged headaches
  • Nose bleeds lasting longer than 10 minutes
  • Coughing up blood
  • Bleeding heavily from gums after brushing teeth
  • Prolonged bleeding from small cuts. To treat cuts, apply pressure with a clean dressing and call a doctor if bleeding does not stop within 10 minutes
  • Heavy bleeding at menstrual periods or bleeding between periods
  • Swelling and tenderness or pain in abdomen
  • Vomiting red blood or material that looks like coffee grounds
  • Bowel movements that are loose or containing blood or that are black and bad smelling
  • Urine containing blood or that is dark brown or cloudy
  • Severe, prolonged back pain, without obvious cause
  • If your child falls or suffers a blow to the head, even if they do not lose consciousness or have a headache.

Please note

  • A child who has had rheumatic heart disease must still receive their prophylactic penicillin injection after valve replacement surgery.

Contact us

If you still have any questions or concerns after the appointment, please contact the relevant care coordinator.

Queensland Paediatric Cardiac Service
Queensland Children’s Hospital
501 Stanley Street, South Brisbane
t: 07 3068 1627
t: 07 3068 1111 (general enquiries)

In an emergency, always call 000.

If it’s not an emergency but you have any concerns, contact 13 HEALTH (13 43 25 84). Qualified staff will give you advice on who to talk to and how quickly you should do it. You can phone 24 hours a day, seven days a week.

Resource No: FS087. Developed by Queensland Paediatric Cardiac Service. Updated: June 2018. All information contained in this sheet has been supplied by qualified professionals as a guideline for care only. Seek medical advice, as appropriate, for concerns regarding your child’s health.

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