inr for warfarin monitoring ©bpac nz, october 2006

nzbpacbetter edicin m e

INR for warfarin

monitoring

©bpacnz, October 2006


Key Messages

• A systematic and methodological approach is needed for managing warfarin therapy

• Patient education is an important part of achieving good INR levels

• For most people once the INR is stable, the rate of testing can be extended 4 to 6 weekly


IntroductionGood management of INR levels requires a

systematic approach involving the whole practice team

• Warfarin is the most widely used anticoagulant in NZ

• Use of warfarin is associated with serious risks

• A systematic and methodological approach is needed for warfarin therapy


The role of INR


What is INR?

INR = ( _________ ) ISI

Some people are at particular risk from warfarin therapy

• The large number of variables in controlling INR levels

• There is no standard response to warfarin

• Elderly people often require lower doses of warfarin

• Poor literacy or numeracy skills are associated with poor INR control

Patient PT

Control PT


Low-dose initiation protocols

• Suitable for outpatients

• Safe

• Achieves therapeutic anticoagulation within 3 to 4 weeks

• Reduces the risk of over-anticoagulation


Transfer of care across the primary – secondary interface

High risk due to:

• Poor communication on discharge

• Tablet strengths may be inappropriate for maintenance therapy.

• Other medications, e.g antibiotics, may interact with warfarin.


Transfer of care across the primary – secondary interface…..contd

New Zealand hospitals must effectively transfer the following essential details of warfarin therapy:

• Condition for which warfarin has been prescribed

• Target INR range

• Planned duration of treatment

• Brand and strength of warfarin tablets given

• Last three doses

• Last three INRs

• Date next INR test due


Pre initiation tests

• Complete blood count including platelets

• INR/PR and APTT

• Liver function tests


Detailing the plan for warfarin therapy

The patient notes should contain the following information:

• The patient is on warfarin

• Condition for which prescribed

• Target INR range

• Planned duration of treatment

• Brand of warfarin


Target INR range

• In most situations the target INR range is 2.0 – 3.0


Prescribing warfarin

• All clinicians should use the same brand of warfarin

• Warfarin use: Marevan ~ 95%, Coumarin® ~ 5%

• The brands are not interchangeable and come in different tablet strengths

• Use only 1 mg tablets during initiation to minimise confusion


Drug labelling can highlight the importance of INR monitoring

• Use labelling on warfarin to remind patients of the need for regular blood tests

• Labels such as “PRN” or “as required” may confuse

• A better option may be “Take the dose advised by your doctor or nurse. You need regular INR blood tests to make sure this dose is right for you”


Patient Education

• Patients who understand what they are doing, benefit more from treatment


Patient education must to cover:

• Need for patient to remind their health professional they are receiving warfarin

• Requirement for regular blood tests

• Adherence to dosage changes after blood tests

• Importance of avoiding other medications except with medical advise

• Significance of illness, such as diarrhoea, infection or fever

• Ability to recognise the signs of bleeding


Signs of possible bleeding

• Red or dark brown urine

• Severe headache

• Excessive menstrual bleeding

• Dizziness, trouble breathing or chest pain

• Dark, purplish or mottled fingers or toes

Indications to call the doctor immediately:

• Red or dark brown stool

• Unusual weakness

• Prolonged bleeding from gums or nose

• Unusual pain, swelling or bruising

• Vomiting or coughing up blood


“The red book”• Facilitates patient education

• Means of sharing information

• Patients should always show to any health professional

• Clinicians and pharmacists should asking to see the book

• The book should be kept up to date.


Monitoring INR

• A reasonable standard of warfarin therapy is an INR within the target range 60% of the time

• Regular testing of INR levels is essential

• Once the INR is stable the rate of INR testing can be extended to 4 to 6 weekly in most people


For patients initiated with low-dose protocol

(warfarin initial dose 2 – 3mg daily):

Initially:

• When INR < 4: Weekly

• When INR > 4: Every 2-3 days until stable for 2 consecutive tests

• Then: fortnightly until stable for 2 - 3 consecutive tests

• Maintenance: Most patients can be extended to 4 – 6 weekly testing however a minority may require more frequent testing.


For patients initiated with higher doses:

• Initially: daily for at least five days until stable for 2 consecutive tests

• Then: every 3 – 5 days until stable for 2 consecutive tests

• Then: weekly until stable for 2 - 3 consecutive tests

• Then: fortnightly until stable for 2 - 3 consecutive tests

• Maintenance: Most patients can be extended to 4 – 6 weekly testing however a minority may require more frequent testing.


Changes in INR levels

Changes in the INR level in a usually stable patient may be due to a number of reasons:

• Non-adherence to dosage regimen

• Drug interactions (pharmaceutical or herbal)

• Major changes in diet or alcohol intake

• Systemic or concurrent disease

• Unknown causes


Managing alterations in the INR

• Changes in weekly doses are usually not required for minor fluctuations.

• For more significant fluctuations in the INR use a standard guide to assist dose modification.


Managing Overanticoagulation

INR 5 – 8 without bleeding

1. Stop warfarin

2. Restart in reduced dose when INR < 5

3. Test INR daily until stable

4. Given Vitamin K 0.5 – 1 mg oral/sc if INR fails to fall, or reversal required within 24 – 48 hours


Managing Overanticoagulation….contd

INR > 8 with minor bleeding

1. Stop warfarin

2. Consider admission if clinical appropriate

3. Restart in reduced dos when INR < 5

4. Given Vitamin K 1 – 2 mg oral/sc


Managing Overanticoagulation….contd

High INR and major bleeding

1. Stop warfarin

2. Give Vitamin K 10 mg sc

3. Admit stat


Sample collection for INR

• Collect blood into a light blue top tube

• The tube must be filled completely

• View the patient handbook

• Ask questions specific to warfarin control, for example:

Adherence to the dosing regimen, Any changes in diet Any medications the patients may have

stopped or started Signs of bleeding


Ceasing warfarin therapy

• Warfarin therapy can be discontinued abruptly at the end of treatment period

• Prospective studies have not indicated a rebound prothrombotic state


Dental extractions and preoperative warfarin doses

• For minor surgical procedures aim for a target INR of approx 2.0 on the day of surgery

• Stop warfarin at least three days prior to major surgery

• When INR < 3.0 warfarin does not need to be stopped for dental extractions


Warfarin and pregnancy

• Pregnant women should never take warfarin, as it is teratogenic

• Women on warfarin should contact their doctor urgently if they think they are pregnant.


Managing warfarin in rest homes

• In rest homes there may be several health professionals involved in the prescribing, dose adjustment and administration of warfarin.

• Clear written instructions are necessary to guide rest home staff.

• Verbal instructions should be avoided whenever possible.


Near patient testing

• Near patient testing (NPT) of INR levels is effective for selected patients

• NPT is risky for patients who are unmotivated or do not understand the process

• NPT requires high standard of quality assurance procedures


Resources available from bpacnz for INR monitoring

• Evidence based guide “INR monitoring”

• Interactive online quiz

• Quiz feedback

• Clinical audit pack for general practice

visit

www.bpac.org.nz

inr for warfarin monitoring ©bpac nz, october 2006

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