Non-reversible inhibitor of COX 1 and COX 2
Cyclooxygenase is responsible for prostaglandin, prostacyclin and thromboxane synthesis. The blocking of thromboxane A2 formation in platelets reduces the ability of platelets to aggregate which has lead to the widespread use of low-dose aspirin in cardiovascular disease. Until recent guidelines changed all patients with established cardiovascular disease took aspirin if there was no contraindication. Following the 2010 technology appraisal of clopidogrel this is no longer the case ^.
Two recent trials (the Aspirin for Asymptomatic Atherosclerosis and the Antithrombotic Trialists Collaboration) have cast doubt on the use of aspirin in primary prevention of cardiovascular disease. Guidelines have not yet changed to reflect this. However the Medicines and Healthcare products Regulatory Agency (MHRA) issued a drug safety update in January 2010 reminding prescribers that aspirin is not licensed for primary prevention.
What do the current guidelines recommend?
Potentiates
Aspirin should not be used in children under 16 due to the risk of Reye's syndrome. An exception is Kawasaki disease, where the benefits are thought to outweigh the risks.
^ NICE now recommend clopidogrel first-line following an ischaemic stroke and for peripheral arterial disease. For TIAs the situation is more complex. Recent Royal College of Physician (RCP) guidelines support the use of clopidogrel in TIAs. However the older NICE guidelines still recommend aspirin + dipyridamole - a position the RCP state is 'illogical'
Nasal polyps are a common finding in patients with aspirin sensitivity, forming part of the Samter's triad (aspirin sensitivity, asthma and nasal polyps). Aspirin can exacerbate respiratory symptoms by inhibiting the cyclooxygenase pathway of arachidonic acid metabolism, leading to an overproduction of leukotrienes. This causes bronchoconstriction and inflammation in sensitive individuals.