What are the recommended loading and maintenance doses of aspirin and ticagrelor, and when should each be administered in the setting of acute myocardial infarction?

Aspirin and Ticagrelor Dosing in Acute Myocardial Infarction

In acute MI, give aspirin 162-325 mg loading dose (chewed, non-enteric coated) immediately on presentation, followed by 75-100 mg daily maintenance, and ticagrelor 180 mg loading dose followed by 90 mg twice daily. 1

Loading Doses - Administer Immediately on Presentation

Aspirin

• Loading dose: 162-325 mg orally 1
• Must be chewed (non-enteric coated) to achieve faster onset of antiplatelet action 1
• Give this loading dose even if the patient is already on chronic aspirin therapy 1, 2
• Timing: As soon as possible on presentation, regardless of whether invasive or conservative strategy is planned 1

Clinical Pearl: Recent evidence shows that patients with acute MI already on chronic aspirin who receive a loading dose (200-500 mg) achieve 6-fold greater thromboxane A2 suppression compared to continuing 100 mg alone, with 53% having inadequate platelet inhibition without the loading dose 2. This translates to better left ventricular function.

Ticagrelor

• Loading dose: 180 mg orally 1
• Timing: Should be administered as early as possible, ideally at first medical contact 3, 4
• Prehospital administration is superior: When given by EMS before hospital arrival, ticagrelor achieves better TIMI 3 flow (91.4% vs 82.2%), better ST-segment resolution (76.3% vs 64.5%), and reduced 30-day MACE (5.4% vs 11.2%) without increased bleeding 3

Maintenance Doses

Aspirin

• 75-100 mg daily (non-enteric coated) 1
• Critical: When using ticagrelor, aspirin must be ≤100 mg daily 1
  • Post-hoc analysis of the PLATO trial showed worse outcomes with higher aspirin doses when combined with ticagrelor 1
• Full-dose aspirin (300-325 mg daily) for 30 days after loading was not superior to low-dose and caused more bleeding 1

Ticagrelor

• 90 mg orally twice daily 1
• Continue for 12 months in ACS patients 5

Timing Algorithm

1. At first medical contact (ideally prehospital via EMS):

   • Aspirin 162-325 mg (chewed)
   • Ticagrelor 180 mg

2. Starting next day through 12 months:

   • Aspirin 75-100 mg daily
   • Ticagrelor 90 mg twice daily

3. After 12 months: Typically transition to aspirin monotherapy (though this is beyond the scope of acute dosing)

Evidence Strength

The 2025 ACC/AHA/ACEP/NAEMSP/SCAI guidelines provide Class 1 (strong) recommendations for:

• P2Y12 inhibitor plus aspirin in all ACS patients (Level A evidence) 1
• Ticagrelor or prasugrel over clopidogrel in STEMI with primary PCI (Level B-R evidence) 1
• Ticagrelor in NSTE-ACS managed conservatively (Level B-R evidence) 1

Common Pitfalls to Avoid

1. Don't skip the aspirin loading dose in patients already on aspirin - they still need it for adequate platelet inhibition 2
2. Don't use high-dose aspirin maintenance with ticagrelor - keep aspirin ≤100 mg daily to avoid worse outcomes 1
3. Don't delay ticagrelor until catheterization - prehospital administration improves reperfusion and outcomes 3, 4
4. Don't use enteric-coated aspirin for loading - it delays onset of action 1

Special Considerations

Contraindication: Do not use ticagrelor with strong CYP3A4 inhibitors like itraconazole - this is contraindicated per FDA labeling 6

Bleeding risk: While ticagrelor increases dyspnea as a side effect, major bleeding rates are acceptable when used appropriately. Prehospital administration does not significantly increase bleeding (4.39% vs 1.39%, p=0.142) 4.