What is the recommended dosage of aspirin (acetylsalicylic acid) in the management of an anterior myocardial infarction (MI)?

Aspirin Dosing in Anterior Myocardial Infarction

For an anterior MI, administer 162-325 mg of non-enteric-coated aspirin immediately (chewed or crushed), followed by 81 mg daily indefinitely for maintenance therapy. 1

Initial Loading Dose

Give 162-325 mg of non-enteric-coated aspirin immediately upon diagnosis or suspicion of MI, with the patient chewing or crushing the tablet for rapid buccal absorption. 1, 2

• The 162 mg dose has Level of Evidence A support, while the 325 mg dose has Level of Evidence C support 1, 2
• This loading dose applies equally to anterior STEMI and should be administered as soon as possible, ideally in the prehospital setting when ACS is suspected 1
• Never use enteric-coated formulations for the loading dose, as they delay absorption by hours 2
• The loading dose achieves a 23% relative risk reduction in 5-week vascular mortality when given within 24 hours 1

Evidence Supporting the 162 mg Dose

While both doses are guideline-recommended, the 162 mg loading dose may be preferable as it appears as effective as 325 mg but with lower bleeding risk. 3

• A large analysis of 48,422 STEMI patients treated with fibrinolytics found no difference in 24-hour mortality (2.8% vs 2.9%), 7-day mortality (4.9% vs 5.2%), or 30-day mortality (6.5% vs 7.1%) between 162 mg and 325 mg 3
• However, moderate/severe bleeding was significantly higher with 325 mg (9.3% vs 12.2%, adjusted OR 1.14) 3
• This suggests 162 mg may be as effective and safer than 325 mg for acute treatment 3

Maintenance Dosing

After the loading dose, continue with 81 mg daily indefinitely for secondary prevention. 1, 4

• The 81 mg daily maintenance dose is preferred over higher doses to minimize bleeding risk while maintaining efficacy 1, 4
• This dose reduces serious vascular events by 1.5% per year in secondary prevention 4
• Meta-analyses demonstrate similar efficacy across doses from 75-1500 mg daily for long-term prevention, but doses below 75 mg show reduced benefit 5, 1

Bleeding Risk Considerations

The maintenance dose of 75-162 mg is specifically recommended because higher doses increase bleeding without additional efficacy. 5

• Analysis from the CURE trial showed major bleeding rates of 2.0% with <100 mg aspirin, 2.3% with 100-200 mg, and 4.0% with >200 mg daily 5
• Therefore, maintenance doses of 75-162 mg are preferred, with 81 mg being the most commonly recommended dose in current practice 5, 1

Location-Specific Considerations for Anterior MI

The aspirin dosing regimen is identical regardless of MI location—anterior, inferior, or lateral infarctions all receive the same aspirin protocol. 1, 6

• Anterior MIs with ST-segment elevation in two or more anterior precordial leads should receive aspirin as described above 6
• The location of the MI does not alter aspirin dosing, though it may influence other therapies such as ACE inhibitor use 6

Critical Implementation Points

Aspirin must be administered immediately upon suspicion of MI, even before definitive diagnosis, and can be initiated by emergency medical services in the prehospital setting. 1, 2

• The only contraindications are aspirin allergy, active bleeding, or documented aspirin intolerance 1
• For aspirin-allergic patients, use clopidogrel 75 mg daily as an alternative 4
• Continue aspirin indefinitely as part of comprehensive secondary prevention 1, 4