Best practice guidelines for oral anticoagulation
Prior to starting treatment routine blood samples should be taken for:
prothrombin time (PT)
activated partial thromboplastin time (APTT)
platelet count
liver function tests (LFTs).
A Trust anticoagulant chart should be used. Warfarin or Sinthrome should also be prescribed on the drug kardex with an instruction 'see chart for dosing'.
Oral anticoagulation should be prescribed for 5pm. Ideally this should be done by the medical team looking after the patient and NOT left to the on call team.
Heparin/LMWH should not be discontinued until the INR is within the therapeutic range (within 0.5 units of the target INR) and the patient is clinically stable.
The standard loading dose is 10mg on days 1 and 2 and 5mg on day 3. (See A/C card for details)
Modifications may be necessary:
if baseline anticoagulation results are abnormal;
if the patient is elderly;
if there are risk factors, e.g. CCF, liver disease;
if the patient is on drugs known to potentiate oral anticoagulants.
Daily measurement of INR for 4 days is recommended when treatment is commenced. Once the INR is in the desired range (within 0.5 units of the target INR) the INR should be monitored every 3rd day until control is stable and then every 5 to 7 days thereafter.
Discharge arrangements must be documented in the patient's notes. An appointment must be made for further INR measurement within 7 days of discharge.
Patients must be given an anticoagulant booklet prior to discharge.
Only 1mg tablets are dispensed by the Trust pharmacy unless there are special circumstances. This reduces the possibility of patients confusing strengths which may lead to overdose.
Note: Sinthrome 2mg is equivalent to warfarin 3mg.
When starting or stopping drugs, consider the effect on anticoagulation.
For patients maintained on anticoagulants
DO NOT do INR's too frequently. Every 3rd day is adequate if acutely unwell or on interacting drugs. Every 5th day is adequate if patient is stable.
If changing dose think about % increase, i.e. 1 mg to 2 mg is a 100% increase while 5mg to 6 mg is only a 20% increase. If usual dose is < 5 mg a change of 0.5 mg/day will usually be suitable. If usual dose > 6 mg a change of 1 mg/day would be more suitable. Changes of >1 mg/day are only needed in exceptional circumstances.
Look at the dose up to 5 days before the current INR to ascertain what dose change is needed.
Give new dose for at least 3 days before rechecking INR.
If INR high
Do not need to omit unless INR > 4 unless bleeding complications.
See BNF chapter 2, oral anticoagulants for guidance on management or consult a haematologist for advice. The haematologist must be alerted to patients with an INR >8 and those with bleeding problems.
Stopping for 1 day will bring the INR down by approximately 1 (2 days by 2 etc). Prescribe reduced dose for 3 days then recheck INR.
If expected high result (i.e. dose too high, drug interaction, acutely ill, malnutrition, alcohol) stop for necessary number of nights then prescribe reduced dose for 3 days then recheck INR.
If one off unexpected result stop for necessary number of days then revert to usual dose and recheck INR in 3 days.
If INR low
Only be concerned if INR < 1.5 (range 2 - 3) or 2 < (range 3 - 4).
If one off result with no apparent cause, give extra loading dose for one or two nights then revert to usual dose with recheck INR in 3 days.
If expected low result (i.e. dose too low, drug interaction, missed doses or Vitamin K/FFP given) give extra loading dose for one or two nights and then prescribe increased dose for 3 days and then recheck INR.
Remember: If you need to decrease warfarin dose due to interacting drugs, illness, malnutrition, you will need to revert to the old dose once these factors are no longer an issue (i.e. if stop interacting drug). Vice versa for increasing doses.
If you have any problems consult your ward pharmacist or the Haematology department
Guidelines on oral anticoagulation: Third edition. Br J Haematol 1998; 101: 374-87
Trust Medicines Information Centre
Dr Kanyiki Consultant Haematologist
May 2003