Anticoagulant drugs Flashcards
Features of venous thrombosis?
Low pressure system
Platelets not activated
Activates coagulation cascade, rich in fibrin clot
What effect does anti thrombin have on the coagulation cascade?
Inhibits Thrombin
Inhibits factors VIIa, Xa, IXa and XIa
Mode of action of heparin>
Potentiates antithrombin causing anticoagulation
Features of heparin?
Immediate effect
IV or S/C
Differences between unfractionated heparin and LMWH?
LMWH have greater inability to inactivate factor Xa and less effect on thrombin and platelet function–> less tendency to cause bleeding
No monitoring needed for LMWH as less interactions (anti Xa assay in rare circumstances)
How can unfractionated heparin be monitored
APTT
Activated partial thromboplastin time
Complications of heparin?
Bleeding
Heparin induced thrombocytopenia (monitor FBC)
Osteoporosis with long term use (due to effect on osteoclast activity)
Heparin reversal?
Stop heparin
Occasionally in severe bleeding:
- Protamine sulphate which reverses antithrombin effect
Partial reversal for LMWH
Full for unfractionated
What effect does vitamin K have on clotting factors?
II, VII, IX and X
Causes final carboxylation of these (adding COOH group)
Mechanism of action of warfarin?
Inhibition of vit K
Why are patients more likely to clot acutely when starting warfarin for the first 2/3 days?
Protein C and S (natural anticoagulants) are affected first in warfarin treatment, need to give heparin for 1st week
If second COOH group is not present on the clotting factor what is the consequence?
Chemical bond is too weak for effective attachment of coag factor to platelet –>Failure of cascade
How is warfarin metabolised?
Enzyme CYP450
How is INR calculated?
Patients PT/ Mean normal PT
to power of international sensitivity index
Adverse effects of Warfarin?
Haemorrhage
Drug interactions
