Select country
Membership information
0800 561 9000
Medicolegal advice
0800 561 9090
Refine my search

Anticoagulant monitoring and dosing

Post date: 07/11/2017 | Time to read article: 7 mins

The information within this article was correct at the time of publishing. Last updated 14/11/2018

Written by a senior professional

We have teamed up with NHS Improvement for a new series of risk warnings based on data from the National Reporting and Learning System (NRLS), the NHS’s national database of patient safety incidents in England and Wales. Each article will tackle a different risk commonly reported to the NRLS. In this issue we tackle a commonly reported incident type, medication errors associated with anticoagulants.

Dr Martyn Diaper, Head of Patient Safety (Primary Care) at NHS Improvement HS

Improvement is excited to have teamed up with Medical Protection to bring you this series of articles, highlighting the most common risks reported to the NRLS. 

We recently launched a new reporting tool - the GP eform, designed to make it quick and easy for GPs and the entire practice team to report patient safety incidents for national and local learning. It also provides evidence of reporting and reflection. Key features include the facility to:

  • receive a bounce back email with national reporting trends;
  • share the incident with the local CCG and NHS England team;
  • save the incident report as evidence for CPD, appraisal, revalidation and CQC inspections. 

Early adopter practices have reported over 2,000 incidents in the first year since the GP eform was launched. From these reports medication-related incidents were identified as the most common incident type, making up around 50% of the total. Of these, around 10% relate to anticoagulants, predominantly warfarin. Emerging themes relating to warfarin incidents include:

  • Failure to monitor – for example, patients continuing to receive prescriptions for warfarin without having their INR levels monitored for many months; or not undertaking the required additional monitoring when another medication is prescribed that concomitantly affected INR levels.
  • Wrong dose/strength – for example, a patient having been prescribed both warfarin 5mg and 0.5mg strengths and then inadvertently taking the wrong strength. 
  • Contraindications – for example, a patient prescribed another medication that interacts with warfarin (e.g. miconazole oral gel);
  • Communication issues across care settings – for example, incomplete/unclear discharge planning information when discharged on warfarin from hospital. 

Patients vary in how they respond to warfarin. This, and a narrow therapeutic range means it’s a fine balance between achieving the right INR to prevent thrombotic events while avoiding the risk of excessive bleeding. It is therefore imperative that we report incidents nationally and learn from things that go wrong, so that lessons can be learnt locally to improve safety and support colleagues who undertake prescribing, monitoring, dosing and supply of warfarin.

Julie Price, Head of Risk Management and Education Consultancy at Medical Protection

Around one billion prescription items were issued in primary care in 2015, costing around £9.3 billion1. According to the PRACtICe study 20122, one in 20 prescription items was associated with a clinically important error and one in 550 was associated with a serious error. Prescribing errors in primary care can cause considerable harm, with adverse drug events accounting for around 7% of hospital admissions in the UK, and half of these are judged to be preventable.3

Evidence from a systematic literature review4 revealed that 47% of all serious medication errors were caused by seven drugs or drug classes:

  • methotrexate;
  • warfarin;
  • nonsteroidal anti-inflammatory drugs (NSAIDS); 
  • digoxin;
  • opioids;
  • aspirin;
  • beta-blockers. 

The PRACtICe study2 also found that simvastatin, warfarin, ramipril and bendroflumethiazide accounted for over 60% of drug preparations associated with monitoring errors.

As seen from the evidence above and from the incidents reported to the NRLS, warfarin accounts for a substantial proportion of medication errors.

How can a practice prevent a potential error, associated with warfarin, occurring? 

The NRLS identified emerging themes for incidents reported. Below is risk management advice for each theme:

Failure to monitor

  • It is essential that a practice has a robust monitoring system in place and always checks the current INR result and any untoward INR trends before generating repeat prescriptions for warfarin. • The practice should also implement appropriate strategies to ensure nonattendees are identified and monitored. If a patient fails to attend for a blood test or is not at home (for a domiciliary visit), the practice should schedule a new appointment within a set time, perhaps one week.
  • If no result is available, eg, the patient has undergone the test in the hospital clinic and no result is available, the GP should telephone the clinic to request the result. It may be helpful to discuss with the hospital warfarin clinic how INR results could be delivered in a timely way to the practice prior to the practice issuing a prescription. 
  • The National Patient Safety Agency (NPSA) states: “Ensure that before issuing a repeat prescription for anticoagulant medication, the GP checks that the patient’s INR is being monitored regularly and that it is at a safe level for the repeat prescription to be issued. The easiest way to do this is to ask to see the patient-held INR record, which may be in the form of a single printed sheet, a small booklet or another format used locally.”5
  • The patient’s yellow warfarin booklet should be updated at every INR test. If this booklet is not available, a temporary record booklet must be completed and given to the patient. The patient should be encouraged to take the booklet to every appointment.

Wrong dose/strength

  • The NPSA states in Patient Safety Alert no. 18: “It is essential for the safe use of anticoagulants that patients and carers receive adequate verbal and written information about their treatment. This information should be provided before the first dose of anticoagulant is administered, and reinforced at hospital discharge, at the first anticoagulant clinic appointment, and when necessary throughout the course of their treatment. It is important that the healthcare practitioner who first provides this information records in the patient’s healthcare records that this information has been supplied.”6
  • NHS Cumbria in Warfarin Management Guidelines (para 16.3) states that: “Wherever possible the patient should not be provided with more than two strengths of warfarin. Tablets should be routinely supplied in 1mg and 3mg strengths to ensure a consistent approach across primary and secondary care and minimize the risk of confusion. In exceptional circumstances eg, high warfarin sensitivity or high dosage requirements, warfarin may be prescribed in 0.5mg or 5mg strengths. In these instances the prescription must indicate the strength prescribed in both numbers and words (‘half mg’ or ‘five mg’) to ensure that the correct tablet is given. The patient should be supplied with the least number of different strengths of tablets possible.”7

Contraindications and interactions

  • It is important that prescribers consider interactions between warfarin and commonly prescribed medicines or complimentary medicines. It is important not to overlook over-thecounter and herbal products; certain food substances can also interact with prescribed medication. Prescribers should refer to latest BNF for a list of drugs known to interact with warfarin.
  • Advise the patient to inform a healthcare professional (including anticoagulant clinic staff, GP, dentist, pharmacist, or nursing staff) of changes to their lifestyle, for instance if he/she starts, stops, or changes the dose of other medications. Other medicines include not only prescribed drugs, but also products that may be bought without prescription, such as aspirin and medicines containing aspirin, vitamins, food supplements, and herbal or homeopathic remedies.8

Communication issues across care settings

  • Discharge arrangements for warfarin monitoring should be clearly established and documented. Responsibility for the discharge arrangements lies with the clinician referring the patient. Patients should remain the responsibility of the hospital team until arrangements and agreement have been made with the GP to take over.
  • The front of the patient’s yellow warfarin booklet should be completed to include indication of treatment, INR target range and duration of treatment, person with clinical responsibility and emergency contact number. The patient’s GP should contact the initiating hospital if any of these details are omitted.

Nominated anticoagulant lead for the practice

Practices should consider nominating a clinical member of the practice staff to be responsible and oversee the provision of the warfarin monitoring services. The nominated person should understand the whole care pathway and review this periodically to identify potential problems. In particular, the nominated clinical person should ensure:

  • There is a system for identifying all INR test results, which includes patients seen on home visits;
  • There is a failsafe system which ensures all results are received and appropriate action taken;
  • Patients are aware of how they will be informed of their INR result, dosing instructions and recall date;
  • Patients with specific needs are identified and appropriately managed, ie, where there are communication problems, patients in social care settings, patients using Monitored Dosage Systems etc. 

In addition a GP should be available at all times for advice when warfarin monitoring services are offered to patients by the practice. 

Delegation of anticoagulant monitoring to other healthcare professionals 

In our experience GPs frequently delegate the role of anticoagulant monitoring (and sometimes dosing) to other healthcare professionals, eg, practice nurse, practice pharmacist, healthcare assistant. Practices may use a computer decision support system for monitoring and dosing patients on warfarin.

In Good Medical Practice9 the GMC makes clear that if a GP delegates this task to another healthcare professional the GP must ensure that the healthcare professional is trained and competent to undertake the tasks delegated to him/ her, and that accountability is clear. He/she should be supervised and work to practice protocols.

It is important to have a robust protocol in place for monitoring those patients who are taking warfarin. This should be reviewed regularly, and issues raised about the system in place addressed. Please see Box 1.

The protocol should be available to all staff, including locums, be signed and dated by staff and reviewed on a regular basis. Warfarin clinic practitioners should also follow other the relevant protocols including infection control, needlestick injuries, venous sampling, disposal of clinical waste and spillages.

Example of what to include in the practice warfarin protocol 

A warfarin clinic protocol for another Healthcare professional (HCP) including HCA, should address requirements for safe practice such as history taking, record keeping and ‘safety netting’. They should include:

  • The name of the nominated anticoagulation lead for the practice (usually a GP);
  • The minimum frequency of face to face review by the supervising doctor and the information to be recorded at a review (preferably using a computer template);
  • The training that the HCP should have completed initially and the required regular update training;
  • The written information that must be provided to patients about issues such as interactions, lifestyle restrictions while taking anticoagulants and symptoms that might indicate dangerous dosages;
  • The history items to be recorded by the healthcare professional at each encounter (preferably using a computer template);
  • How patients’ responses to questions and their concerns should be recorded and dealt with by the Healthcare professional;
  • Circumstances that must immediately and invariably be reported to the supervising doctor by the HCP;
  • What the HCP should do if an INR is outside normal limits at the time of testing; 
  • Who is responsible for action if a patient cannot be contacted by phone by the doctor;
  • Procedures to prevent patients being ‘lost to follow-up’ if they miss an appointment with the HCP (some INR monitoring computer packages have a specific facility to flag nonattendees);
  • Audit arrangements for monitoring the clinic


  1. Health and Social Care Information Centre, Prescription cost analysis (2016)
  2. Avery et al, Investigating the prevalence and causes of prescribing errors in general practice: The PRACtICe study. (2012) Commissioned by GMC
  3. Stock S et al, Examining variations in prescribing safety in UK general practice: cross sectional study using the Clinical Practice Research Datalink (2015) BMJ 2015;351:h5501 
  4. Saedder et al, Identifying high-risk medication: a systematic literature review (2014) Eur J Clin Pharmacol. 2014 Jun;70(6):637-45. doi: 10.1007/s00228-014-1668-z. Epub 2014 Mar 27.
  5. National Patent Safety Agency, Anticoagulant therapy: information for GPs (2007) 
  6. NHS Cumbria, Warfarin Management Guidelines (2014)
  7. National Institute for Health and Care Excellence (NICE) Anticoagulation – oral. Scenario: Warfarin (October 2015) 
  8. General Medical Council, Good Medical Practice (2013)

Share this article

New site feature tour

Introducing an improved
online experience

You'll notice a few things have changed on our website. After asking our members what they want in an online platform, we've made it easier to access our membership benefits and created a more personalised user experience.

Why not take our quick 60-second tour? We'll show you how it all works and it should only take a minute.

Take the tour Continue to site

Medicolegal advice
0800 561 9090
Membership information
0800 561 9000

Key contact details

Should you need to contact us, our phone numbers are always visible.

Personalise your search

We'll save your profession in the "I am a..." dropdown filter for next time.

Tour completed

Now you've seen all of the updated features, it's time for you to try them out.

Continue to site
Take again