What is the role of Acetylsalicylic acid (Aspirin) as an antiplatelet medication?

From the Guidelines

Aspirin is a highly effective anti-platelet medication for preventing cardiovascular events, particularly in patients with established cardiovascular disease or those at high risk, with a recommended daily dose of 75-100 mg. The use of aspirin as an anti-platelet medication is supported by numerous studies, including a meta-analysis of large randomized trials that showed a decrease of 10 to 20 vascular events and 1 to 2 additional cases of major GI bleeding for every 1000 patients treated with aspirin 1. Aspirin works by irreversibly inhibiting cyclooxygenase-1 (COX-1), which prevents the formation of thromboxane A2, a compound that promotes platelet aggregation and blood clotting 1.

Key Points to Consider

• The anti-platelet effect of aspirin lasts for the lifetime of the platelet (approximately 7-10 days), which is why even a single daily dose provides 24-hour protection 1.
• Common indications for aspirin include secondary prevention after heart attack or stroke, management of stable coronary artery disease, and prevention of clotting in patients with stents.
• Patients should take aspirin with food to minimize gastrointestinal irritation and should be aware of potential side effects including bleeding (especially gastrointestinal), bruising, and allergic reactions.
• Aspirin should not be stopped suddenly without medical advice as this can lead to a rebound effect with increased risk of clotting.
• For those unable to tolerate aspirin, alternative anti-platelet medications like clopidogrel (75 mg daily) may be considered 1.
• In acute coronary syndromes, a loading dose of 325 mg aspirin is often given, followed by the lower maintenance dose.

Special Considerations

• The role of aspirin in primary prevention remains unproven, and the decision to add aspirin in hypertensive patients should be taken in accordance with the total cardiovascular risk 1.
• A recent meta-analysis of six RCTs found no statistically significant reduction in the risk of major cardiovascular events or all-cause mortality when aspirin was compared with placebo or no aspirin in people with diabetes and no pre-existing CVD 1.
• Aspirin significantly reduced the risk of myocardial infarction in men, but not in women, and evidence relating to harm was inconsistent 1.

Recommendation

Based on the most recent and highest quality study, low-dose aspirin (75-100 mg daily) is recommended for patients with established cardiovascular disease or those at high risk, due to its proven effectiveness in reducing the risk of cardiovascular events 1.

From the Research

Aspirin as an Anti-Platelet Medication

• Aspirin is the most commonly prescribed antiplatelet agent, with a strong evidence base for its efficacy in secondary prevention of ischemic events in patients with established cardiovascular disease 2.
• However, its role in primary prevention has been subject to controversy over the past decades, with historical trials showing only modest benefit in terms of reduction of ischemic events, mostly myocardial infarction and to a lesser extent stroke, and only at the expense of an increased risk of bleeding 2, 3.

Efficacy of Aspirin in Primary Prevention

• Recent results from three trials of primary prevention have shown either no benefit or modest benefit on combined ischemic end points, without any impact on hard cardiovascular events such as myocardial infarction or stroke, accompanied by an increased risk of bleeding 2.
• Aspirin reduces the risk for myocardial infarction in men and strokes in women, but does not seem to affect cardiovascular disease mortality or all-cause mortality in either men or women 4.
• The use of aspirin for primary prevention increases the risk for major bleeding events, primarily gastrointestinal bleeding events, in both men and women 4.

Current Recommendations and Future Directions

• The current recommendations on the use of aspirin for primary prevention have been downgraded due to the neutral net benefit or even harm associated with its use in patients with no overt cardiovascular disease 2.
• A new, platelet-guided approach to the study of prophylactic aspirin therapy has been proposed, which involves quantifying platelet activity to identify individuals at elevated cardiovascular risk due to a hyperreactive platelet phenotype 5.
• This approach may reveal a population with hyperreactive platelets who will benefit most from primary cardiovascular disease prevention with aspirin, and usher in a new era of precision-guided antiplatelet therapy 5.