Flashcards in Anticogulant Drugs Deck (43):
What are you targeting in prevention of venous thrombosis?
What is a natural inhibitor of fibrin clot formation?
Anti thrombin III
What does heparin do?
How long does it take for heparin to work?
How do you give heparin?
Can also be given IV in rare situations
Why isn't unfractionated heparin used anymore?
Very narrow theraputic window - LMWH is better
How does heparin potentiate antithrombin?
Binds to Antithromibin to stabilise the link between it and thrombin or Xa.
What test do you use to monitor heparin?
APTT if unfractionated
Anti Xa assay for LMWH but not really used in clinical practice
What test do you do to monitor warfarin?
What other assay is occasionally used in heparin monitoring?
Why is APPT used in heparin monitoring?
APPT much more sensitive to heparin therapy
Why do you monitor FBC in heparin?
Risk of Heparin Induced Thrombocytopenia (HITT)
If platelet count drops call haematology
Give a long term risk of heparin
What should you do if you get a low platlet count n someone who is on heparin
- Contact haematology
- Stop heparin
Start other anticoagulant
What do you do in the case of bleeding in a patient who is on heparin?
Does heparin have a short of long half life
Short ~ 12 hours
What is the antidote to heparin?
Protamine sulphate. This reverses antithrombin effect. Only partially effects LMWH as it does not have an effect on Factor Xa
Why does protamine sulphate only partially reverse the effect of LMWH?
Does not have an effect on Factor Xa
Where is Vitamin K absorbed?
What dos Vitamin K require for absorption?
What clotting factors require Vitamin K?
What are the first clotting factors to fall when warfarin is started?
Protein C and S
Why do you need to have 5 days of initial heparin therapy with warfarin?
Different half lives of the clotting factors
How does vitamin K activate clotting factors?
Carboxylation of glutamic acid
Where is warfarin metabolised?
Liver - Cytochrome p450 pathway
What metabolises warfarin?
How do you start warfarin therapy?
Loading high dose with heparin. Monitor closely and then titrate down
If AF and they haven't had a blood clot then start slowly
When should warfarin be taken?
At the same time every day
What do you use to monitor warfarin therapy?
What is the equation for INR?
PT is seconds/Mean normal PT is seconds x International Sensitivity Index
What is the target INR in patients on warfarin?
2 - 3
If you have an INR of 5 are you more at risk of bleeding or clotting?
What are the side effects of warfarin?
What is the risk of an intracerebral haemmorhage in people on warfarin therapy?
1/200 per year
How do you reverse warfarin therapy?
1. Omit warfarin dose (this will take several days to get INR back into target range)
2. Oral vitamin K (takes about 6 hours)
What do you do if the INR is above 8 or if there is significant bleeding in a patient on warfarin?
Give oral vitamin K
What do you do if there is severe bleeding in a patient on warfarin?
1. Stop warfarin
2. Oral Vitamin K
3. Clotting factor administration
How long does it take for oral vitamin K to work?
What do you give to reverse warfarin therapy if you need an immediate reversal?
What are the two classes of new anticoagulants?
Oral direct thrombin inhibitors (Dabigatran)
Oral Xa inhibitors (Rivaroxaban)
Name a factor Xa inhibitor?
What is the advantage of Xa inhibitors over thrombin inhibitors?
Not renally excreted - won't cause kidney injury