Treatments and tests

Warfarin safety

Safe warfarin use means reducing the risk of a blood clot forming in your body, without increasing the risk of bleeding. To do this your International Normalised Ratio (INR) needs to be within the target range.

What can I do to keep my International Normalised Ratio within the target range?

These include:

  • taking your warfarin exactly as prescribed
  • having regular blood tests exactly as recommended
  • making dose changes exactly as instructed
  • not stopping or starting any medicines without talking with your doctor
  • not making any major changes to your diet
  • limiting your alcohol consumption to 1 to 2 standard drinks per day
  • consulting your doctor if you become ill.
How should I take warfarin?

Warfarin should be taken:

  • exactly as prescribed by your doctor
  • once a day – during the evening is recommended.

Warfarin dose

Always take exactly the right dose. If you accidentally take too much warfarin, contact your doctor.

Warfarin brands come in different strength tablets. Your doctor may give you a prescription for more than one tablet strength to make up the right dose. The tablets are colour coded to help identify different strengths. Always check the label and the tablet colour so you have the right brand and tablet strength.

If you are unsure of the dose or which strength and colour tablets to use ask your doctor or pharmacist.

Read more about warfarin and the different types of tablets.

When should I take warfarin?

Take your warfarin exactly as prescribed by your doctor. That means taking the exact dose once a day at about the same time.

Warfarin can be taken before, with or after a meal. The time you take warfarin needs to fit into your daily routine. Taking the dose with the evening meal is a good idea. If an evening dose doesn’t suit you, talk to your doctor.

What if I miss a dose?

You should:

  • never skip a dose or take a double dose of warfarin
  • make sure you always have enough tablets.

It is very important to take your warfarin every day. To help you remember, mark off your dose in your diary, calendar or warfarin treatment card after you take it.

Special dose aids like Dosette boxes or a Webster-pak® can help. Ask your pharmacist about dose aids.

Make sure you plan ahead:

  • if you run out of tablets or cannot reach your doctor, visit the nearest doctor or hospital
  • before you travel consider having an extra prescription filled or ask your doctor for a spare prescription to take with you.

What if I only just missed taking my warfarin?

If it is only a few hours since you missed your warfarin dose then you should take your usual dose at once.

If you take warfarin with your evening meal and miss a dose, the missed dose can be taken any time before you go to sleep.

What if I missed my warfarin yesterday?

If it is more than a few hours since you missed a dose (for example, the next day), then don’t take the missed dose. Take the next dose instead at the usual time.

Do not change the dose. Doubling up the dose is dangerous.

Make a note that you have missed that dose and tell your doctor at the time of your next blood test.

What if I miss more than 1 dose?

If you miss your warfarin for more than 1 day, talk to your doctor for more advice.

How can I monitor my warfarin treatment?

You need to have regular blood tests. After each test, the doctor will tell you what dose to take each day and when your next blood test is due.

You must have regular blood tests to check the INR. If the INR is not within your target range your doctor may change your warfarin dose.

It is best to get your blood test in the morning, as the result will be available the same day.

Find out your INR result and the warfarin dose to take before your next dose is due. You should also ask for the date of your next blood test.

You should have a blood test at least once a month, but sometimes you will need to have them more often.

Write down the dose and test results for your records. Most patients keep a record on a card or in a special booklet.

What if I am ill?

If you are ill this may change the effect of warfarin in your body and your INR.

Contact your doctor if you experience:

  • vomiting or diarrhoea
  • fever or infection
  • loss of appetite
  • jaundice
  • any other illness.
What do I need to remember about my medicines?
  • Don’t stop taking your medicines or change the dose unless told to by your doctor.
  • Your medicines are yours alone. Don’t share medicines with anyone else.
  • Store all medicines out of reach of children.
  • Keep medicines securely in one place, away from light, heat and moisture.
  • Keep medicines in their original packets with all the labels and instructions.
  • Ask your pharmacist for help with containers and dosage aids.
  • Check expiry dates often – do not take out-of-date medicines. Take expired medicines to your pharmacist for safe disposal.
  • Keep an up-to-date list of all your medications.

Where to get help

Medic Alert

Medicines information line

Poisons information line

  • Immediate specialist advice for overdoses or poisoning
  • Phone 13 11 26 (local call rates from land line only)

Adverse Medicines Events Line

National Prescribing Service (NPS) MedicineWise

  • Visit NPS MedicineWise (external site) for information on warfarin and other medications.
  • Do not skip doses of warfarin – always have extra supplies available.
  • You need to have regular blood tests to monitor your INR.

Remember

  • Do not skip doses of warfarin – always have extra supplies available.
  • You need to have regular blood tests to monitor your INR.

Acknowledgements

Western Australian Therapeutic Advisory Group | The WA Medication Safety Group


This publication is provided for education and information purposes only. It is not a substitute for professional medical care. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your healthcare professional. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified healthcare professional for a diagnosis and answers to their medical questions.

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