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High risk medicines: anticoagulants

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Anticoagulants are used to prevent the blood from clotting as normal.

They treat and prevent blood clots. Examples of anticoagulants include:

  • warfarin
  • non-vitamin K antagonist oral anticoagulants (also known as DOACs or NOACs). This includes apixaban, rivaroxaban, edoxaban and dabigatran
  • injectable anticoagulants (also known as low molecular weight heparins)

The common side effect of all anticoagulants is bleeding. NOACs do not carry the same level of bleeding risk as warfarin. They do not need routine blood tests. People must take these medicines as prescribed to maintain blood clotting.

Information and awareness

People taking anticoagulants should have enough information to use them safely and effectively. The NICE guideline on venous thromboembolic diseases says that people should know:

  • how to use anticoagulants
  • how long to take anticoagulation treatment
  • possible side effects of anticoagulant treatment and what to do if these occur
  • the effects of other medications, foods and alcohol on oral anticoagulation treatment
  • how to monitor their anticoagulant treatment
  • how anticoagulants may affect their dental treatment
  • what to do if they are planning pregnancy or become pregnant
  • how anticoagulants may affect activities such as sports and travel
  • when and how to seek medical help

Injectable heparins

These are often prescribed for prevention of blood clots in patients after surgery.

Injectable heparins are normally prescribed as pre-filled syringes. The person can administer these by subcutaneous injection. Manufacturers recommend that the site of administration is rotated.

If you are responsible for administering, you should have relevant training and competence. A care plan should be in place to support the use of injectable heparins.

Dispose of used syringes in a sharps bin.

Non-vitamin K antagonist oral anticoagulants (DOACs/NOACs)

NICE provides guidance about NOACs and their place in therapy.

Some of these medicines do not have reversal agents. You should take extra care that doses are given as prescribed.

NOACs must be given at the prescribed dose and frequency. Their duration of action is shorter than that of warfarin. The anticoagulant effect of NOACs fades 12–24 hours after taking the last dose. Omitting or delaying doses could lead to a reduction in anticoagulant effect. This would cause a higher risk of blood clots.

Some NOACs can be given once or twice a day depending on why they are prescribed.

If someone misses a dose of a NOAC, you need to know what action to take and record this. For example, you should contact the pharmacist for advice about taking the next dose. You should also inform the person’s GP.

Do not dispense dabigatran in a dosette box. Store it in its original container to protect from moisture.


People taking warfarin need regular blood tests.

Blood tests are more frequent at the start of treatment. They may become less frequent once the person is on stabilised treatment.

The maximum time between blood tests is 12 weeks.

Regular blood tests measure the International Normalised Ratio (INR). This is a measure of how fast the blood clots. INR blood tests can be done at the GP practice or hospital. Specialist clinics might test blood depending on the services they provide.

The dose prescribed often changes in response to the blood test. So it is often prescribed 'as directed'. Make sure you are aware of the person's current warfarin dose.

The National Reporting and Learning Service issued an alert to highlight the importance of warfarin compliance and monitoring. The service produced a booklet (commonly known as 'the yellow book'). The booklet and supporting information should be given to all people taking warfarin.

The booklet explains important information about:

  • the medicine
  • how to take it
  • how to recognise side effects
  • how to keep track of ongoing blood monitoring

INR blood test results should be in writing. This could be in the patient's handheld yellow INR record book. Or the results could be in direct written communication from the prescriber.

The person should usually take warfarin at the same time each day.

If a person takes too much or too little warfarin, you must contact their GP.

If you are responsible for administering warfarin, you should accurately record how much is administered each time. You can do this on the MAR or on other appropriate forms.

Warfarin interacts with many medicines. This includes over the counter medicines and herbal products. If a person starts a new medicine, the GP and pharmacist should check for any interactions. If the person needs any over the counter medicines, you must consult the pharmacist first. They need to know that the person is on warfarin.

Drinking cranberry juice might increase the effect of warfarin.. The same is true for other cranberry products such as capsules or concentrates.

People should not consume large amounts of alcohol when taking warfarin.

Be aware of known side effects of warfarin. These include spontaneous, severe or prolonged bruising, blood in the urine or faeces.

Always tell the GP if the person taking warfarin has a fall. They are at a higher risk of internal bleeding. Often they will need to be managed or assessed in secondary care.

Last updated:
02 December 2019