CPTP 2.6 Drugs and blood clotting Flashcards
Three types of drugs used in patients with thrombosis
Anticoagulants
Antiplatelet agents
Fibrinolytic agents
Describe arterial thrombus and venous thrombus
Arterial thrombus
- Slow formation
- Larger white head
- Firm and hard
- Formed by turbulence and rupture
- Treated by antiplatelet agent
Venous thrombus
- Fast formation
- Larger red tail
- Soft
- Formed by low pressure/ stagnation
- Treated by anticoagulant agents
Four classes of anticoagulant
- Heparin and LMWH
- Warfarin
- Selective factor Xa inhibitors
- Direct thrombin (factor IIa) inhibitors
How does heparin work in the body?
Inhibits coagulation by activating ATIII
Inhibits (intrinsic pathway) clotting factors IX, Xa, XI and XII (especially Xa)
Prevent coagulation (not to break down fibrin webs already formed)
Clinical use of heparin
Monitored using APTT test (for intrinsic pathway)
Treat venous thromboembolism and cardiac disease.
Rapid onset of action, need frequent dosing
Given IV
How does warfarin work in the body?
Inhibits K-dependent clotting factors (VII, IX, Xa, II)
Metabolised by CYP450 enzymes in the liver
Clinical use of Warfarin
Orally given
Slow onset of action, so Heparin is used until Warfarin shows its effect
Venous thrombosis, pulmonary embolus
Monitored using NRI test (for extrinsic)
Direct thrombin (factor IIa) inhibitors
e.g. dabigatran
Inhibitor of thrombin
Orally given
Rapid onset of action
Prevention of stroke and embolism in patients with atrial fibrillation
Three steps of platelet-plug formation
- Platelet adhesion (vWF)
- Platelet secretion (thromboxane A2, ADP, serotonin, PAF)
- Platelet aggregation
Antiplatelet drug e.g. aspirin
Inhibits COX1 and so inhibits the synthesis of TXA2
Used prophylactically to prevent arterial thrombosis leading to stroke, MI and transient ischemic attack
Fibrinolytic drugs
e.g. alteplase
Activate conversion of plasminogen to plasmin which breaks down fibrin, thus dissolves clots
IV, immediate effect
