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Protocol for initiating Warfarin (Slow initiation) in Primary Care.


Atrial Fibrillation is a common and serious heart arrhythmia associated with thromboembolic stroke.

The CHADS2 score is a clinical prediction rule for estimating the risk of stroke in patients with non rheumatic atrial fibrillation

In clinical use, the CHADS2 score has been superseded by the CHA2DS2-VASc score that gives a better stratification of low risk patients.

It is recommended that the GRASP – AF tool is used to identify existing high risk patients who are not receiving an anticoagulant.

Whilst the use of aspirin in patients with a CHADS2 score of 1 or above is still supported by QOF  Recent evidence for use of aspirin as primary prophylaxis in patients at high risk of CVD suggests negligible net benefit (De Berardis et al, 2009; Fowkes, et al 2010). For these patients currently receiving aspirin reconsider anti coagulation as an option.

It is important that an assessment of bleeding risk should be considered before starting anti coagulation. The HAS-BLED score is recommended to assess bleeding risk in A/F patients, however remember stroke and bleeding share risk factors.

A HAS-BLED score of >3 indicates an increased one-year bleed risk on anticoagulation which would be sufficient to justify caution or more frequent evaluation. Where a patient scores 1 point for labile INR, a score of >4 would indicate a need for caution.

 Recommendations by BCSH guideline refers to target INRs rather than target ranges, although the target range is generally taken to be within 0.5 of the target therefore target INR of 2.5 equates to target range of 2.0 – 3.0.

Patients with AF who require warfarin for the prevention of cardio-embolic should have an INR target of 2·5


Guideline for Initiating Warfarin in Primary Care

General practitioners may initiate warfarin in the community, usually in older patients with atrial fibrillation, when urgent anticoagulation is not required. This guideline is only intended for initiating warfarin over several weeks in non-acute situations.

Anticoagulation urgency?  If urgent initiation required refer.


Existing patients taking warfarin for non-valvular atrial fibrillation

WARFARIN REMAINS A SUITABLE FIRST-LINE ORAL ANTICOAGULANT FOR MOST PATIENTS.

Conversion to NOAC recommended for patients:

. intolerant of vitamin K antagonists (VKA)

. resistant to the effects of warfarin (failure to get into the therapeutic range despite dose escalation)

. TTR < 65% after > 3 months (despite good compliance with warfarin)

NOACS are still black triangle drugs; whilst they have a shorter half-life than warfarin, they have no simple anti dote. Whilst they don’t need anti coagulation monitoring, there is no standardised easy way of measuring their effectiveness. Conversely, warfarin has been in use for over 60yrs its effects are measureable and can be rapidly reversed in the event of major bleeding.



Exclusion criteria

SENSITIVITY TO WARFARIN LIKELY Interacting drugs analgesics, amiodarone, some

antibacterials, St John's Wort,antiepileptics, antifungals, lipidlowering drugs, some

ulcer healing drugs? (See BNF)

Liver disease abnormal liver function or raised PTR

Other diagnoses heart failure, low weight, age >80

Alcohol intake high raised GGT.

If concerned about sensitivity, consider more frequent monitoring for 2, then 4 and eventually to 12 weeks

Consider seeking specialist advice



IMPORTANT NOTES ABOUT THE GUIDELINE

• It is only intended for initiating warfarin over several weeks in non-acute situations.

• It is based on a validated protocol for similar patients being warfarinised in a hospital outpatient clinic (Oates et al. A new regimen for starting warfarin therapy in outpatients. Br J Clin Pharm 1998;46:157-161).

 It is intended to give an INR of 2.0-3.0 at 6 weeks. Patients with an INR target outside this range may still begin anticoagulation in this way with further adjustments made after 6 weeks.

• INRs are only required at weekly intervals.

• The dose of warfarin only changes if the INR is >3.0 or persistently <2.0.

• The INR at day 14 predicts the maintenance dose – any subsequent changes are based on routine INR checks at days 21, 28,

35 and 42.

• Once the INR is stable, the time between monitoring can be increased to 2, then 4, and eventually 12 weeks as recommended

by the British National Formulary.

• Patients should have their liver function tests [including prothrombin time], urea and electrolytes, creatinine and full blood count measured prior to treatment.

• Patients should always be provided with a treatment booklet containing appropriate information about safe use of warfarin.

Further information about oral anticoagulation can be obtained from:

• British Society of Haematology Guidelines (www.bcshguidelines.com)

• SIGN 36 on Antithrombotic Therapy (www.sign.ac.uk)


NOAC`s are recommended as an option where warfarin is either contraindicated or where the patient has a documented hypersensitivity to or intolerance of coumarin anticoagulants severe enough to cause treatment withdrawl. In situations where repeated international normalised ratio (INR) testing/monitoring may be impractical, the use of NOAC should be considered. However increased bleeding risk is a contraindication to warfarin this also applies to the NOACS.


 

NOACs are not a suitable alternative to warfarin in patients with bleeding complications associated with warfarin treatment, contraindications to warfarin therapy due to a high bleeding risk, poor compliance with warfarin therapy or trivial side effects related to warfarin.


The decision about whether to start a NOAC should be made after an informed discussion between the clinician and the patient about the risks and benefits of anticoagulants in particular NOAC compared to warfarin.


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