prophylactic treatment for hip surgery and surgery for femur fractures (short to medium term)
treatment of venous thromboembolism - deep vein thrombosis (DVT) or pulmonary embolism (PE) (1)
anticoagulation for 1 month is inadequate treatment after an episode of VTE
at least 6 weeks anticoagulation is recommended after calf vein thrombosis and at least 3 months after proximal DVT or PE
for patients with temporary risk factors and a low risk of recurrence 3 months of treatment may be sufficient
for patients with idiopathic VTE or permanent risk factors at least 6 months anticoagulation is recommended
target INR of 2·5 is recommended for long-term oral anticoagulant (VKA) therapy for secondary prevention of VTE
target INR of 2·5 is recommended for patients with DVT or PE associated with antiphospholipid syndrome
target of 3·5 is also recommended for patients who suffer recurrence of VTE whilst on warfarin with an INR between 2·0 and 3·0
cardioversion (1)
target INR of 2·5 is recommended for 3 weeks before and 4 weeks after cardioversion
to minimise cardioversion cancellations due to low INRs on the day of the procedure a higher target INR, e.g. 3·0, can be used prior to the procedure
peripheral arterial thrombosis and grafts
antiplatelet drugs remain first line intervention for secondary antithrombotic prophylaxis. If long-term anticoagulation is given to patients at high risk of femoral vein graft failure a target INR of 2·5 is recommended (1)
coronary artery thrombosis
if oral anticoagulant therapy is prescribed a target INR of 2·5 is recommended (1)
systemic embolism after MI
mitral stenosis with embolism (long term)
atrial fibrillation (long-term) - it may be safer to aim for an INR of 2 in those aged over 75 years (3)
risk of stroke is 3 times greater in patients with atrial fibrillation with mitral stenosis than in those without valve disease - based on its apparent effectiveness in non-randomized studies and its effect in non-rheumatic atrial fibrillation, warfarin is usually given to maintain an INR of 2.5 (5)
INR 3.0 or more
treatment of recurrent DVT, PE (long term)
target of 3·5 is also recommended for patients who suffer recurrence of VTE whilst on warfarin with an INR between 2·0 and 3·0
prosthetic heart valves (long-term)
for patients in whom valve type and location are known specific target INRs are recommended (1)
bileaflet valve (aortic) 2·5
tilting disk valve (aortic) 3·0
bileaflet valve (mitral) 3·0
tilting disk (mitral) 3·0
caged ball or caged disk (aortic or mitral) 3·5
otherwise a target INR of 3·0 is recommended for valves in the aortic position and 3·5 in the mitral position (1)
Notes (1):
bioprosthetic valves:
long-term warfarin not required in absence of atrial fibrillation
oral anticoagulants are not required for valves in the aortic position in patients in sinus rhythm, although many centres anticoagulate patients for 3?6 months after any tissue valve implant
patients with bioprostheses in the mitral position should receive oral anticoagulants to achieve an INR of 2.5 for the first 3 months. After 3 months, patients with atrial fibrillation should receive lifelong therapy to achieve an INR of 2.5
patients with bioprosthetic valves with a history of systemic embolism and those with intracardiac thrombus should also be anticoagulated to achieve an INR of 2.5
patients who do not require oral anticoagulants after the first 3 months may be considered for antiplatelet therapy, e.g. aspirin
INR values and risk of haemorrhage versus risk of thromboembolism in treatment of DVT/PE
risks of haemorrhage and thromboemboli are minimized at international normalized ratios of 2-3. Ratios that are moderately higher than this therapeutic range appear safe and more effective than subtherapeutic ratios (6)
Reference:
1. Baglin TP et al. British Committee for Standards in Haematology - Guidelines on oral anticoagulation (warfarin): third edition - 2005 update British Journal of Haematology 2006; 132 (3): 277-285.
2. MeReC Bulletin (1997); 8 (1): 1-4.
3.MeReC Bulletin (2002), 12 (5), 17-20.
4. MeReC Bulletin (2003); 13(4): 13-16.
5.British Committee for Standards in HaematologyGuidelines on oral anticoagulation: third edition British Journal of Haematology 1998;101 (2); 374-387.
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