Anticoagulants, antifibrinolytic and antiplatelet drugs Flashcards
What are the stages of haemostasis?
Constriction of damaged vessels
Mechanical blockage of hole by platelet plug
Coagulation cascade
Thrombolysis
What causes platelet activation and aggregation?
Thromboxane A2 (TXA2)
ADP
Thromboxane
what is the purpose of fibrinogen?
Links adjacent platelets
Other than TXA2, what activates platelets?
Thrombin
When does thrombolysis occur?
Fibrin mesh is prevented from increasing so is slowly dissolved by plasmin
What 3 stages can drugs target?
Platelets - anti-platelet
Coagulation - anti-coagulant
Thrombolysis - thrombolytic therpay
What is the most common anti-platelet drug?
Aspirin
Indications for antiplatelet therapy?
Previous MI Previous stroke stable angina Claudication Atrial fibrillation
what kind of anti-platelet drug is aspirin?
Cyclooxygenase inhibitor
Function of cyclooxygenase?
Formation of thromboxane
Mechanism of action of cyclooxygenase inhibitors like aspirin?
Inhibit the formation of thromboxane - stop platelet activation and aggregation
What dose is aspirin given prophylactically?
75mg/day
What dose is aspirin given in emergency?
300mg/day
Contraindications of aspirin?
Allergies Age less than 12 GI bleeding Bleeding disorder Severe liver disease
How do ADP receptor antagonists work?
Inhibit binding of ADP so platelet aggregation cannot occur
When are ADP receptor antagonists (clopidogrel) chosen over aspirin?
Safer in GI bleeding
Less toxicity
What drugs can clopidogrel (ADP receptor antagonist)?
Proton pump inhibitors
When are adenosine re-uptake inhibitors used? (dipyridamole)
Prosthetic heart valves, alternative or in addition to aspirin
When is dipyridamole (adenosine re-uptake inhibitor) contraindicated?
Uncontrolled angina - may exacerbate
Mechanism of action of anticoagualnt like heparin?
Vitamin K antagonist
Enhance antithrombin III
Inactive prothrombin
Impair platelet function
Why can heparin not be given through GI tract?
Poorly absorbed
How is heparin adminsitered?
Low dose = subcutaneous
High dose = Iv
Why are low molecular weight heparin sometimes used?
Once daily dosing
No need to monitor
Smaller bleeding risk
Reduced risk of thrombocytopeaenia
What are the disadvantages of low molecular weight heparins?
Less reversible than heparin
Unwanted effects of heparin?
Haemorrhage
Thrombocytopenia
Allergy
What kind of drug is warfarin?
Anti-coagulant - vit K antagonist
Why is warfarin slow acting?
Highly protein bound
How can warfarin be reversed?
Vit K
Disadvantages of warafarin?
Drug interactions with everything
Warfarin uses?
Prevent DVT (deep vein thrombosis)
Treatment of PE (pulmonary embolism)
Atrial fibrillation - prevent risk of embolisation
Prosthetic heart valves to prevent emboli developing on valves
Problems with warfarin?
Increased risk of bleeding (unless INR is less than 4)
How do thrombolytics work?
Plasminogen activators (degrades clots)
What is an indication for thrombolysis
Arterial thrombosis
When is INR value required?
For procedures where there is a risk of bleeding extractions Surgery that involves making a flap extensive RSI IDB
What is the threshold INR value for no risk of bleeding?
4
How does dabigatran work?
Direct thrombin inhibtor
Disadvantage of direct oral anticoagulants?
No INR value - dont know how bleeding will go
