4. Anticoagulant and antiplatelet drugs

Question 1

Anticoagulants

Answer 1

warfarin

heparin:
unfractionated and lmw heparin

newer agents:

• dabigatran (oral direct thrombin (factor IIA) inhibitor
• rivaroxaban - oral direct factor Xa inhibitor

antiplatelet drugs

antifibrinolytics

Question 2

Warfarin mechanism of action and INR

Answer 2

vit K antagonist
prevents gamma carboxylation of factors II, VII, IX, X

prolongs extrinsic pathway - prothrombin time
monitored by INR

target INR 2.5 for DVT/PE and AF, 3.5 for recurrent VTE or metal heart valves

Question 3

Target INRs

Answer 3

target INR 2.5 for DVT/PE and AF

3.5 for recurrent VTE or metal heart valves

Question 4

Metabolism of warfarin

Answer 4

metabolised in liver by CYP2C9

inhibits vit K reductase (VKORC-1) so prevents gamma carboxylation of factors II, VII, IX, X

vitamin K needed for gamma carboxylation of precursor forms of factors II, VII, IX, X, protein C and protein S bound to glutamic acid to gamma-carboxylated glutamic acid version

gamma-carboxylated glutamic acid version will bind to platelet phospholipids