10. Anti-platelets Agents Flashcards
What are the processes involved in homeostasis?
Vessel wall constriction
Platelet adhesion to sub-endothelial collagen, degranulation, aggregation, plug formation
Blood coagulation
Define haemostasis
Arrest of haemorrhage
Define thrombosis
Pathological formation of a “haemostatic” plug within the vasculature in the absence of bleeding
What is virchows traid?
Three broad categories of factors that contribute to thrombosis
Stasis of blood flow
Endothelial injury
Hypercoagulbility
What are the roles of anti platelet drugs?
Critical role for platelets in development of arterial thrombi
Damaged endothelium activates platelets which respond by adhering to endothelium and aggregating
Examples of anti-platelet agents?
Cyclo-oxygenase inhibitors
ADP receptor pathway inhibitor
Phosphodiesterase inhibitors
Mechanism of action of aspririn
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When is aspirin used for clinical indications?
Ischaemic stroke/ TIA Acute coronary syndrome Post Myocardial Infarcation Following coronary bypass Angina Pectoris Peripheral arterial disease/ claudication Atrial fibrillation
What are the adverse effects of aspirin?
Gastric irritation/bleeding
Hypersensitivity reactions
Reyes syndrome in children
What are the drawbacks of aspirin?
Lack of response in some patients
-rare often related to poor drug adherence
Irreversible platelet
-continued bleeding risk for some time after stopping the drug
What is the mechanism of action of clopidogrel?
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What are the clinical indications of clopidogrel?
Secondary prevention in patients intolerant of aspririn
Used with aspirin for 3-12 months after acute coronary syndrome and after procedures to coronary arteries to prevent thrombosis
What are the adverse effects of clopidogrel?
Gastro-intestinal irritation and bleeding
Dyspepsia
Hypersensitivity reactions
What are the potential drawbacks of clopidogrel?
Pro-drug: delayed onset of action
Genetic variation of liver enzymes responsible for metabolism and activation so response varies between individuals
Drug-drug interactions
Irreversible inhibition of P2Y12 receptor
What is prasugrel?
A prodrug but different chemical structure permits conversion to active metabolite in liver
An irreversible inhibitor of platelet P2Y12 receptor but greater absorption and higher metabolite bioavailibilty gives more predictable antiplatlet response than clopidogrel
What is tricagrelor?
A pyrimidine that does not bind to ADP binding site but separate site on P2Y12 receptor to inhibit G-protein signalling
reversible inhibitor of platelet P2Y12 receptor with rapid onset and offset of action
Dipyridamole-mechanism of action
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What are the clinical indications of Dipyridamole?
With oral anticaogulants for prevention of thromboembolism in patients with prosthetic heart valves
Given with aspirin for secondary prevention of ischaemic stroke (TIA)
What are the adverse affects of dipyridamole?
Gastro-intestinal irritation/bleeding Dizziness, flushing and headache Myalgia Chest pain Hypersensitivity reactions
Abciximab –mechanism of action
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What are the clinical indications of Abciximab?
Given with aspirin and heparin during coronary interventions in patients at high risk of MI
What are the adverse effects of Abciximab?
Bleeding
Chest pain
Hypersensitivity
