Antiplatelet Therapy in Acute Myocardial Infarction

Introduction to Antiplatelet Loading Doses

The European Society of Cardiology recommends an antiplatelet loading dose in acute myocardial infarction (AMI) consisting of aspirin 150-325 mg (oral or IV if oral ingestion not possible) plus a P2Y12 inhibitor: clopidogrel 600 mg, prasugrel 60 mg, or ticagrelor 180 mg, with the specific P2Y12 inhibitor choice depending on the management strategy and patient characteristics 1, 2

The American Heart Association recommends administering aspirin as soon as possible after AMI diagnosis is deemed probable at a dose of 150-325 mg in a chewable form (avoid enteric-coated aspirin due to slow onset of action) 1
If oral ingestion is not possible, intravenous administration of aspirin at a dose of 250-500 mg is an alternative 1
After the loading dose, continue with a lower maintenance dose (75-160 mg) orally daily for life 1

For patients undergoing primary PCI, the American College of Cardiology recommends a 600 mg oral loading dose of clopidogrel (preferred over 300 mg due to more rapid and stronger inhibition of platelet aggregation) 1, 3
For patients receiving fibrinolytic therapy, the American Heart Association recommends a 300 mg loading dose of clopidogrel if PCI is performed within 24 hours of fibrinolytic therapy, and a 600 mg loading dose if PCI is performed more than 24 hours after fibrinolytic therapy 2
For patients who received fibrinolytic therapy, the American College of Cardiology recommends prasugrel 60 mg can be given if PCI is performed more than 24 hours after treatment with a fibrin-specific agent or more than 48 hours after a non-fibrin-specific agent 2
The American College of Cardiology recommends a 180 mg loading dose of ticagrelor followed by 90 mg twice daily maintenance dose 4, 5
The American Heart Association recommends a maintenance dose of aspirin of 81 mg daily when used with ticagrelor 4, 5

For patients with STEMI undergoing primary PCI, the American College of Cardiology recommends that both aspirin and a P2Y12 inhibitor should be administered before or at the time of PCI 2
For patients requiring urgent CABG after antiplatelet loading, the American Heart Association recommends that aspirin should not be withheld before urgent CABG, and clopidogrel or ticagrelor should be discontinued at least 24 hours before urgent on-pump CABG, if possible 2

The American College of Cardiology recommends considering patient-specific bleeding risk factors when selecting antiplatelet therapy, including history of bleeding 6
In patients with a history of gastrointestinal bleeding, the American Heart Association recommends considering co-administration of proton-pump inhibitors to minimize the risk of recurrent bleeding 3, 6