💊 Aspirin

Aspirin is a non-steroidal anti-inflammatory drug (NSAID) and an antiplatelet agent. It belongs to the salicylate class.

Aspirin irreversibly inhibits cyclooxygenase (COX-1 and COX-2) enzymes. This prevents the synthesis of prostaglandins and, crucially for its antiplatelet effect, thromboxane A2 (TXA2) in platelets. Reduced TXA2 impairs platelet aggregation and vasoconstriction.

Low-dose aspirin is primarily used for secondary prevention of atherothrombotic events, such as myocardial infarction and stroke. It is also indicated for acute coronary syndromes, including unstable angina and NSTEMI, and for prevention of pre-eclampsia in high-risk pregnancies. Higher doses are used for pain, inflammation, and fever, though less commonly now due to alternatives.

Absolute contraindications include active peptic ulcer disease, aspirin hypersensitivity (including asthma, rhinitis, urticaria induced by aspirin or other NSAIDs), and severe hepatic or renal impairment. It should be avoided in children under 16 due to the risk of Reye's syndrome and in the third trimester of pregnancy due to premature closure of the ductus arteriosus.

Common adverse effects include gastrointestinal irritation, dyspepsia, and nausea. More serious effects include gastrointestinal bleeding, peptic ulceration, and bronchospasm in susceptible individuals. Hypersensitivity reactions, including angioedema and anaphylaxis, can occur. Tinnitus and hearing loss are signs of salicylism with higher doses.

For long-term use, no routine blood monitoring is typically required for low-dose aspirin. Patients should be counselled to report any signs of bleeding (e.g., melaena, haematemesis) or severe dyspepsia. Renal function should be considered in patients with pre-existing impairment or those on concomitant nephrotoxic drugs.

When prescribing, always check for aspirin allergy or NSAID hypersensitivity. Enquire about a history of peptic ulcer disease or gastrointestinal bleeding. Consider interactions with other antiplatelet agents, anticoagulants, and NSAIDs, which increase bleeding risk. Counsel patients on potential GI upset and to report any unusual bleeding.

Aspirin's irreversible COX-1 inhibition in platelets is key to its antiplatelet effect, lasting for the lifetime of the platelet. It is a cornerstone of secondary prevention in cardiovascular disease. Remember the Reye's syndrome risk in children and the GI bleeding risk, especially with concomitant NSAIDs or anticoagulants. Its role in pre-eclampsia prevention is important.

SBA questions often focus on the contraindications, particularly active bleeding or aspirin-induced asthma. Another common theme is the distinction between its antiplatelet use (low dose) and analgesic/anti-inflammatory use (higher dose). Questions might also explore its role in Reye's syndrome or its interaction with other antiplatelet agents.