Anti- platelet and anti- coagulants Flashcards
What is the difference in appearance, consequence and method of prevention of arterial vs venous clots?
Appearance: arterial= red// venous= white
Consequence: A–> MI, stroke// V–> DVT, PE
Prevention: A need anti-platelets, V need anti- coagulants
What activates the intrinsic and extrinsic pathways??
Intrinsic= exposure of tissue factor in basement membrane- activates factor X Extrinsic= abnormal surface (class, collagen) leading to factor XII activation
What 3 factors lead to increased coagulability? (virchows triad)
- abnormality in vessel wall
- abnormality in flow
- abnormality in blood components
How does warfarin work?
inhibits production of vitamin K dependant clotting factors (VII, IX and X)
Why do most people need to take heparin as well for the first 3 days of starting warfarin?
Because it takes a few days for the existing clotting factor to be used up and not replaced
What effect will alcohol and NSAIDS have on warfarins effect?
Both will increase effect, alcohol because it inhibits the CYP enzyme which metabolised warfarin and NSAIDS because it displaces warfarin from plasma proteins it binds to.
Why is warfarin avoided in young women?
It is teratogenic
Name 3 things which will inhibit warfarins effect
Leafy greens, cererals, antiepileptics, rifampicin, st johns wort–> these induce CYP450s
Give 3 indications of warfarin
AF, DVT, PE, prosthetic heart valve
Give 3 side effects of warfarin
bleeding, bruises, severe headache, vomiting, confusion
How can warfarin be reversed?
- Stop warfarin (needs 3 days to get back to normal)
- Give vitamin K IV if acutely unwelll
- Consider giving fresh frozen plasma and prothombin complex concentrate if severe bleeding
- Consider surgery to find source of bleeding
What are the two types of heparin and whats the difference between them?
Low molecular weight heparin- eg dalteparin, daily sub cut injections
Unfractionated heparin - IV bolus infusion
How does heparin work?
Heparins are glycosaminoglycans which bind and activate anti- thrombin III which then deactivates factor Xa. Unfractioned heparin also inhibits IIa by activating anti- thrombin III.
Describe the monitoring required of LMWH and unfractioned heparin
LMWH does need monitoring as response is very predictable. Unfractioned isn’t so requires monitoring
How fast do heparins work?
Fairly rapidly, also reverse fast on stopping use
Briefly describe the initiation of warfarin
Loading dose of 10mg, usually. Dose on second day will depend on INR response, gradually dose lowered until INR is within required range (usually 2-3). Cover first 3 days with heparin.
When is heparin used?
- LMWH peri operatively in low doses as youve removed warfarin
- LMWH during first few days of initiating warfarin treatment
- Reduce reoccurance/ extension of coronary artery thrombosis in unstable angina and MI
- Instead of warfarin in pregnancy
Give 3 ADRs of heparin
- intracranial bleeds
- bleeding at injection sites
- thrombocytopenia (may trigger autoimmune destruction of platelets)
- osteoporosis with long term use
How is heparin reversed?
Using protamine sulphate - dissociates heparin by binding to anti- thrombin III
How does dabigatran work?
It is a thrombin (factor IIa) inhibitor
List 3 anti-platelet drugs
Aspirin, dipyridamole, clopidogrel
How does dipyridamole work? when is it used?
phosphodiesterase inhibitor, this in turn inhibits platelet activation- uses lots in secondary preventions of strokes but can cause flushings and headaches
How does clopidogrel work and when is it used?
ADP antagonist, used in acute coronary syndromes and post PCI
Name two fibrinolytics other than streptokinase
Alteplase, reteplase
How do alteplase and reteplase work?
They are tissue plasminogen activators (tPA), tPA cleaves plasminogen into plasmin, which breaks down fibrin in the clot. It also breaks down fibrinogen systemically (bad), but less so than streptokinase.
