Anticoagulants, Antiplatelets & Thrombolytics Flashcards
Haemostasis
to stop bleeding in haemorrhage
Involves: local vasoconstriction, platelet aggregation and coagulation
Thrombosis
pathological, coagulation in the absence of bleeding
Involves: Virchow’s triad
Virchow’s triad
increase coagulation, vessel damage and abnormal blood flow
Arterial thrombus
white, platelet aggregation, embolus tends to cause stroke
Venous thrombus
red, white head, red-jelly tail, fibrin rich, embolus tends to lodge in lung: PE
Platelets in coagulation cascade
endothelial damage –> platelet aggregation–> mediator (pre-existing (ADP) and newly formed (TXA2)) release, further platelet aggregation
Fibrin in coagulation cascade
endothelial damage –> clotting factor release –> X activated (Xa) –> prothrombin –> thrombin (converts fibrinogen to fibrin (forms a fibrin mesh)
Fibrin clot formation
Platelet aggregation + blood coagulation
Thrombin
fibrinogen to fibrin
Platelet function
brings clotting factors closer together for activation
Activation of clotting factors
gamma-carboxylation
gamma carboxylation enzyme
carboxylase
Essential requirement of carboxylase?
vitamin K - therefore is required for coagulation
Warfarin target?
blocks vitamin K reductase - stopping vitamin K from binding to it (preventing gamma carboxylation and coagulation)
Anticoagulant function?
prevention/ treatment of venous thrombosis/ embolism
Caution with anticoagulants?
risk of haemorrhage
Which clotting factors does warfarin block?
II, VII, IX & X
How is warfarin standardly taken?
orally
Fast or slow action?
slow (2-3 days)
Half life?
long (40 hrs)
Warfarin warnings?
difficulty of balancing anticoagulance with haemorrhage risk - low therapeutic index
Factors that increase haemorrhage risk when on warfarin?
liver disease (less clotting factors) fast metabolism (fast clotting factor clearance) drug interaction: agents that inhibit hepatic metabolism of warfarin drugs that inhibit platelet function (aspirin and NSAIDS) drugs that inhibit reduction or availability of vitamin K
Factors that inhibit warfarin action (increase thrombosis risk)?
physiological state: pregnancy (higher clotting factor synthesis), hypothyroidism (less degradation of clotting factors), vitamin K consumption, drugs that increase the metabolism of warfarin
warfarin overdose treatment?
vitamin K or concentrate of clotting factors