Transcript Louw
Oral anticoagulation
Illse Louw
Contents
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•
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What you should know
Cows and rats and creepy crawlies
INR
Stats
What you should know
• Warfarin is an oral anticoagulant
• It prolongs the time taken for blood to clot
• This reduces the possibility of clot formation
– To prevent harmful blood clots from forming
– To prevent worsening of existing clots
• Too little warfarin – will not prevent clotting
• Too much warfarin – possible bleeding
complications
What you should know
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Take the tablets once a day preferably in evening
The dose must be taken as prescribed
The dose must be monitored with regular lab tests
Keep written record of your target INR, INR results
and dosage
• Regular INR tests
– What is an INR
– What is my INR therapeutic target
• Testing intervals
What you should know
• Be aware of possible bleeding / thrombotic
complications, report
• Keep Vit K content of diet consistent
– Avoid changes to normal eating patterns
– Continue to eat a balanced diet
– Vit K rich foods – cauliflower, cabbage, broccoli,
spinach, brussel sprouts, avocado, liver
• Be aware of drug and intercurrent illness
interactions
What you should know
• Avoid heavy or binge drinking
– Moderate is OK
• Inform health care professional
– Miss a dose or doses
– Change diet or medication
– Surgical or dental procedure planned
– Pregnancy
• Travel
Of rats and cows and humans
• Schofield FW (1924). "Damaged sweet clover; the cause of a new disease
in cattle simulating haemorrhagic septicemia and blackleg". J Am Vet Med
Ass 64: 553–6.
• Roderick LM (1931). "A problem in the coagulation of the blood; "sweet
clover disease of the cattle"". Am J Physiol 96: 413–6
• Stahmann MA, Huebner CF, Link KP (1941). "Studies on the hemorrhagic
sweet clover disease. V. Identification and synthesis of the hemorrhagic
agent". J Biol Chem 138 (2): 513–27
• Dicumarol patented in 1941
• Warfarin patented with Wisconson Alumni Research Foundation
– Initially used as rodenticide
– 1950’s used in humans
Indications and target INR
• Prescribed for conditions such as
– Irregular heart rhythm, artificial heart valves,
stroke ; Clotting in veins
• Guidelines:
– British Committee for Standards in Haematology
2011
– American College of Chest Physicians 2012
– Southern African Society of Thrombosis and
Haemostasis SAMJ 2007 97 1259
Worldwide – patients on warfarin
Country
Population
Patients on OAT
Canada
England
France
Italy
Netherlands
Spain
USA
32 million
63 million
60 million
60 million
16,3 million
42 million
280 million
275 000
750 000
600 000
650 000
325 000
400 000
2,5 million
J Thromb Thrombolysis 2006 21 73
0.9%
1.2%
1%
1.1%
2%
1%
0.9%
Test for effect of warfarin
ISI
Patient PT
INR
Control PT
SSW stats
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•
•
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699 patients
INR < 2: 30%
INR2-4: 65%
INR > 4: 5%
100
90
80
70
63.8%
60
50
Series1
40
30
20
10
0
1
3
5
7
9
11 13 15 17 19 21 23 25 27 29 31 33 35
Make oral anticoagulants more
convenient
• Increase dose interval
– British Guidelines agree with longer intervals
– US 2008 guidelines – 4 wks
– US 2012 12 wkly intervals
• For patients taking VKA with consistently stable INRs we
suggest and INR testing freq of up to 12 weeks
• Unsuitable patients – congestive heart failure, other
major disease developing
– Leads to fewer dose changes
Make oral anticoagulants more
convenient
• Do not correct if one INR out of range
• Stable patients – no change for 3 months
• Then INR =
1.5-1.9
Extra dose
Versus
Continue with usual
3.1-4.4
Withhold dose
or
Versus
Usual
INR @ 2 weeks
60% in TR
56% in TR
… the future
…. new oral anticoagulants