What are the recommended loading doses of aspirin, P2Y12 inhibitors (clopidogrel, ticagrelor, prasugrel), and anticoagulants (unfractionated heparin, enoxaparin, cangrelor) for patients with non‑ST‑segment elevation myocardial infarction (NSTEMI), ST‑segment elevation myocardial infarction (STEMI), and unstable angina?

Loading Doses for NSTEMI, STEMI, and Unstable Angina

For patients with acute coronary syndromes (NSTEMI, STEMI, unstable angina), initiate aspirin 162-325 mg orally (chewed if non-enteric coated) immediately, followed by a P2Y12 inhibitor with ticagrelor 180 mg or prasugrel 60 mg preferred over clopidogrel for STEMI undergoing primary PCI, while clopidogrel 300-600 mg is acceptable for NSTEMI or when potent agents are unavailable. 1

Aspirin Loading and Maintenance

• Loading dose: 162-325 mg orally, chewed when possible for faster onset 1
• Administer immediately upon presentation regardless of management strategy (invasive vs. conservative)
• Maintenance: 75-100 mg daily (non-enteric coated) 1
• If oral route unavailable, use rectal or intravenous administration 1

Critical caveat: When using ticagrelor, aspirin maintenance dose must not exceed 100 mg daily due to increased bleeding risk at higher doses 1, 2

P2Y12 Inhibitor Selection and Loading Doses

For STEMI with Primary PCI:

Prasugrel or ticagrelor are strongly recommended over clopidogrel to reduce MACE and stent thrombosis 1:

• Prasugrel: 60 mg loading dose, then 10 mg daily 1, 3

  • Reduce maintenance to 5 mg daily if weight <60 kg or age ≥75 years 3
  • Contraindicated in patients with prior stroke/TIA 3

• Ticagrelor: 180 mg loading dose, then 90 mg twice daily 1, 2

  • Can be used regardless of treatment strategy (invasive or conservative) 2

• Clopidogrel: 300-600 mg loading dose, then 75 mg daily 1

  • Use only when prasugrel/ticagrelor unavailable, contraindicated, or not tolerated 1

For NSTEMI/Unstable Angina:

The 2025 ACC/AHA guidelines and 2021 ESC guidelines align on prasugrel or ticagrelor preference for patients proceeding to PCI 1, 2:

• Prasugrel: Should be considered in preference to ticagrelor for NSTEMI patients proceeding to PCI 2

  • Same dosing as STEMI (60 mg load, 10 mg daily)

• Ticagrelor: 180 mg loading dose acceptable for any NSTE-ACS patient 1, 2

• Clopidogrel: 300-600 mg loading dose 1, 2

  • May be considered for upstream treatment if angiography delayed >24 hours 1
  • Preferred in elderly patients ≥70 years due to lower bleeding risk without increased ischemic events 4

For STEMI with Fibrinolytic Therapy:

Clopidogrel is the recommended P2Y12 inhibitor when fibrinolysis is used 1:

• 300 mg loading dose if age ≤75 years
• 75 mg initial dose (no load) if age >75 years
• Then 75 mg daily maintenance 1

Important: Prasugrel and ticagrelor are NOT recommended with fibrinolytic therapy—insufficient safety data in this setting 1

Timing Considerations

NSTEMI/Unstable Angina:

• Routine pretreatment NOT recommended when early invasive strategy planned and coronary anatomy unknown 2
• The 2025 guidelines note no clear benefit to prasugrel loading before diagnostic angiography compared to at time of PCI, with increased bleeding risk if early CABG needed 1, 3
• May consider upstream treatment with clopidogrel or ticagrelor if angiography delayed >24 hours 1

STEMI:

• For primary PCI: Administer loading dose as soon as possible, ideally at time of diagnosis 1, 3
• For delayed presentation (>12 hours): May defer until coronary anatomy established 3

Anticoagulation Loading Doses

Parenteral anticoagulation is mandatory for all ACS patients at diagnosis and during revascularization 2:

Unfractionated Heparin (UFH):

• During PCI: 70-100 IU/kg IV bolus (or 50-70 IU/kg if using GP IIb/IIIa inhibitor) 2
• Target ACT: 250-350 seconds (or 200-250 seconds with GP IIb/IIIa inhibitor) 2

Enoxaparin:

• 1 mg/kg subcutaneous every 12 hours for medical management 2
• If pre-treated with subcutaneous enoxaparin, consider IV administration during PCI 2
• Do not crossover between UFH and LMWH 2

Fondaparinux:

• Recommended for medical management or when PCI transfer delayed 2
• Give single UFH bolus at time of PCI if patient on fondaparinux 2

Bivalirudin:

• May be considered as alternative to UFH during PCI 2

Discontinue parenteral anticoagulation immediately after invasive procedure 2

Special Populations and Caveats

Age ≥75 years:

• Prasugrel generally not recommended due to increased fatal/intracranial bleeding risk 3
• Exception: High-risk patients with diabetes or prior MI may benefit 3
• Consider clopidogrel as safer alternative with similar efficacy 4
• If using prasugrel, reduce maintenance to 5 mg daily 3

Weight <60 kg:

• Reduce prasugrel maintenance to 5 mg daily 3
• Increased bleeding risk with standard 10 mg dose 3

Planned CABG:

• Do not start prasugrel if urgent CABG likely 3
• Discontinue prasugrel ≥7 days before surgery when possible 3

GP IIb/IIIa Inhibitors:

• Consider for bail-out only (no-reflow, thrombotic complications) 2
• Not recommended as routine pretreatment when anatomy unknown 2
• Not recommended as triple antiplatelet therapy 2

The evidence strongly supports immediate dual antiplatelet therapy initiation with aspirin plus a P2Y12 inhibitor, with the choice of P2Y12 inhibitor guided by clinical presentation (STEMI vs. NSTEMI), management strategy (PCI vs. fibrinolysis), and patient characteristics (age, weight, bleeding risk).