Anti platelet agents Flashcards
Example of an anti-platelet agent
Aspirin
How do anti-platelet agents work?
Thrombotic events occur when platelet-rich thrombus forms in atheromatous arteries and occludes the circulation. Aspirin irreversibly inhibits cyclooxygenase (COX) to reduce production of the pro-aggregatory factor thromboxane from arachidonic acid, reducing platelet aggregation and the risk of arterial occlusion. The antiplatelet effect of aspirin occurs at low doses and lasts for the lifetime of a platelet (which does not have a nucleus to allow synthesis of new COX) and thus only wears off as new platelets are made.
Indications of anti-platelet agents
For treatment of acute coronary syndrome and acute ischaemic stroke, where rapid inhibition of platelet aggregation can prevent or limit arterial thrombosis and reduce subsequent mortality.
For long-term secondary prevention of thrombotic arterial events in patients with cardiovascular, cerebrovascular and peripheral arterial disease.
To reduce the risk of intracardiac thrombus and embolic stroke in atrial fibrillation where warfarin and novel oral anticoagulants are contraindicated.
To control mild-to-moderate pain and fever (although other drugs are usually preferred, particularly in patients with inflammatory conditions).
Contraindications of anti-platelet agents
Aspirin should not be given to children aged under 16 years due to the risk of Reye’s syndrome, a rare but life-threatening illness that principally affects the liver and brain.
It should not be taken by people with aspirin hypersensitivity, i.e. who have had bronchospasm or other allergic symptoms triggered by exposure to aspirin or another NSAID. However, aspirin is not routinely contraindicated in asthma.
Aspirin should be avoided in the third trimester of pregnancy when prostaglandin inhibition may lead to premature closure of the ductus arteriosus.
Aspirin should be used with caution in people with peptic ulceration (e.g. prescribe gastroprotection) or gout, as it may trigger an acute attack.
Side effects of anti-platelet agents
Common: Gastrointestinal irritation.
Serious: Gastrointestinal ulceration and haemorrhage and hypersensitivity reactions including bronchospasm.
High dose: Tinnitus.
Overdose (Life threatening): hyperventilation, hearing changes, metabolic acidosis and confusion, followed by convulsions, cardiovascular collapse and respiratory arrest.
Interactions of anti-platelet agents
Aspirin acts synergistically with other antiplatelet agents, which although therapeutically beneficial can lead to increased risk of bleeding. Thus, although it may be given with antiplatelet drugs (e.g. clopidogrel, dipyridamole) and anticoagulants (e.g. heparin, warfarin) in some situations (e.g. acute coronary syndrome), caution is required.
Elimination of anti-platelet agents
Renal
Patient information of anti-platelet agents
Aspirin is available for oral or rectal (higher doses) administration.
Advise patients that the purpose of low-dose aspirin treatment is to prevent heart attacks or strokes and to prolong life. Warn them to watch out for indigestion or bleeding symptoms and report these to their doctor if they occur.
