Antiplatelet and Fibrinolytic agents Flashcards
(18 cards)
What is the primary difference between arterial and venous thrombosis?
Arterial thrombosis is typically superimposed on an atheroma, occurs in high-pressure systems, and is primarily composed of platelets (white thrombus). Venous thrombosis, on the other hand, is most commonly caused by stasis, occurs in low-pressure systems, and is mainly made up of coagulation factors and red blood cells (red thrombus).
What are the two common treatments for arterial and venous thrombosis?
For arterial thrombosis, antiplatelet drugs like aspirin and clopidogrel are used. For venous thrombosis, anticoagulants such as warfarin, heparin, and NOACs (e.g., rivaroxaban) are used.
How do prostaglandins contribute to platelet aggregation?
Prostaglandins prevent platelets from spontaneously sticking together. However, when glycoproteins are activated, they promote the conversion of arachidonic acid into thromboxane A2 via cyclooxygenase 1, encouraging platelet aggregation.
How does aspirin work as an antiplatelet drug?
Aspirin is an irreversible COX-1 inhibitor that reduces platelet aggregation by more than 95%. It is typically used at a lower dose (75mg per day) for thromboprophylaxis and in patients who have experienced cardiovascular events.
What is the mechanism of action of clopidogrel as an antiplatelet drug?
Clopidogrel is an irreversible antagonist of the P2Y12 receptor, which ADP activates on platelets. It has a slow onset of action (around 5 days) and is often used in patients who are intolerant to aspirin.
What is the POINT trial, and what did it reveal about combined antiplatelet therapy?
The POINT trial (Johnston et al., 2018) compared clopidogrel and aspirin in acute stroke patients. It found that combined therapy reduced mortality and recurrence of ischaemic strokes but increased the risk of bleeding.
What is abciximab, and when is it used?
Abciximab is a glycoprotein IIb/IIIa receptor antagonist that inhibits all platelet activation pathways. It is used in high-risk patients undergoing coronary angioplasty and has shown effectiveness in treating refractory unstable angina.
What are the main mechanisms of action of dipyridamole?
Dipyridamole inhibits phosphodiesterase, blocks adenosine uptake, and reduces ADP levels. It also inhibits thromboxane A2 synthesis. When combined with aspirin, the effects are additive.
How does epoprostanol work in preventing thrombosis?
Epoprostanol (PGI2) inhibits platelet activation and induces vasodilation. It is used in haemodialysis to prevent thrombosis and has a short half-life, so its side effects are brief.
What are fibrinolytic drugs used for, and what are some examples?
Fibrinolytic drugs, such as streptokinase, alteplase, tenecteplase, reteplase, and urokinase, are used to break down clots by converting plasminogen into plasmin. They are primarily used in conditions like acute myocardial infarction, thrombotic stroke, life-threatening deep vein thrombosis, and pulmonary embolism, though they may increase the risk of bleeding.
What is the role of thromboxane A2 in platelet aggregation?
Thromboxane A2 promotes platelet aggregation by encouraging platelets to stick together. It is produced from arachidonic acid through the action of cyclooxygenase 1 (COX-1).
What is the usual dose of aspirin for antiplatelet therapy, and why is it used at this dose?
Aspirin is typically used at a lower dose of 75mg per day for antiplatelet therapy. This dose is effective for thromboprophylaxis and to prevent further cardiovascular events, without causing excessive bleeding.
How long does it take for clopidogrel to reach its full effect?
Clopidogrel has a slow onset of action, taking about 5 days to reach its full effect.
In which patients is clopidogrel typically used instead of aspirin?
Clopidogrel is typically used in patients who are intolerant to aspirin.
What is the major limitation of using abciximab in treatment?
The major limitation of using abciximab is that it is limited to single use in high-risk patients undergoing coronary angioplasty.
How does dipyridamole enhance the effect of aspirin in platelet inhibition?
Dipyridamole enhances aspirin’s effect by inhibiting phosphodiesterase, blocking adenosine uptake, and reducing ADP levels, which further reduces platelet aggregation when combined with aspirin.
What is the clinical use of epoprostanol, and how does it work?
Epoprostanol (PGI2) is used to prevent thrombosis in haemodialysis. It works by inhibiting platelet activation and inducing vasodilation. It has a short half-life, so its side effects are brief.
What are some common side effects of fibrinolytic drugs like alteplase and streptokinase?
The main side effect of fibrinolytic drugs such as alteplase and streptokinase is an increased risk of bleeding.
