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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 direct oral anticoagulants (DOACs) or novel oral anticoagulants (NOACs). These include apixaban, rivaroxaban, edoxaban and dabigatran
  • injectable anticoagulants - also known as low molecular weight heparins

The most common side effects of all anticoagulants are bleeding and bruising. They are considered critical medicines and must be given at the prescribed times to make sure they are effective.

Information and awareness

People taking anticoagulants should have accessible 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

This information should be included in a care plan to support the use of anticoagulants.

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 a person cannot self administer the injection, a healthcare professional may administer. Or this can be delegated to a care worker. You must provide relevant training and assess the competency of care workers who accept this responsibility. A care plan should be in place to support this delegated task. For more information, see delegating medicines administration.

Dispose of used syringes in a sharps bin.

Non-vitamin K antagonist oral anticoagulants (DOACs)

DOACs must be given at the prescribed dose and frequency. Their duration of action is shorter than that of warfarin. The anticoagulant effect of DOACs 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 DOACs can be given once or twice a day depending on why they are prescribed.

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

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

People who take DOACs and injectable anticoagulants must have blood tests:

  • before starting treatment and
  • at intervals throughout treatment as specified by the prescriber.


People taking warfarin need regular blood tests. Where necessary people should be supported to access monitoring and testing.

Blood tests are more frequent at the start of treatment to ensure the person is on the correct dose. 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 a pharmacist first. They need to know that the person is on warfarin. Refer to the yellow book for information on how certain foods can affect INR levels.

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. For more detail on side effects, visit the NHS page on warfarin.

Always tell the relevant healthcare professional 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.

Prescribers may decide to switch people from Warfarin to a DOAC to reduce the need for blood tests.

People should not be taking both warfarin and a DOAC. If you see this combination, check with the prescriber before giving.

Last updated:
12 October 2020