Loading Doses in Myocardial Infarction
For acute MI, administer aspirin 162-325 mg loading dose immediately, followed by a P2Y12 inhibitor loading dose (clopidogrel 600 mg, prasugrel 60 mg, or ticagrelor 180 mg) as early as possible before or at the time of PCI. 1, 2
Antiplatelet Loading Doses
Aspirin
- Loading dose: 162-325 mg orally (non-enteric coated, chewed when possible for faster absorption)
- Administer immediately upon presentation to all STEMI and NSTE-ACS patients without contraindications
- Continue with maintenance dose of 75-100 mg daily indefinitely 1, 2
P2Y12 Inhibitors - Primary PCI Setting
For STEMI undergoing primary PCI, choose one of the following:
- Clopidogrel: 600 mg loading dose 1
- Prasugrel: 60 mg loading dose (preferred over clopidogrel for better outcomes) 1, 2
- Ticagrelor: 180 mg loading dose (preferred over clopidogrel) 1, 2
Critical contraindication: Do not use prasugrel in patients with prior stroke or TIA - this carries a Class III Harm recommendation 1, 3
P2Y12 Inhibitors - Post-Fibrinolytic PCI Setting
The loading dose timing depends on when PCI occurs after fibrinolysis:
If no prior clopidogrel loading dose given with fibrinolytic:
- PCI ≤24 hours after fibrinolysis: Clopidogrel 300 mg 4
- PCI >24 hours after fibrinolysis: Clopidogrel 600 mg 4
- Prasugrel 60 mg: Only if PCI >24 hours after fibrin-specific agent or >48 hours after non-fibrin-specific agent 4
If already received clopidogrel loading dose with fibrinolytic:
- Continue 75 mg daily without additional loading dose 4
Anticoagulant Loading Doses
For Primary PCI
Unfractionated Heparin (UFH):
- With planned GP IIb/IIIa inhibitor: 50-70 units/kg IV bolus
- Without GP IIb/IIIa inhibitor: 70-100 units/kg IV bolus
- Adjust additional boluses to maintain therapeutic ACT (250-300 seconds with HemoTec device or 300-350 seconds with Hemochron device) 1
Bivalirudin:
- 0.75 mg/kg IV bolus, then 1.75 mg/kg/hour infusion
- Additional 0.3 mg/kg bolus can be given if needed
- Preferred over UFH with GP IIb/IIIa inhibitor in high bleeding risk patients 1
Fondaparinux: Class III Harm - do not use as sole anticoagulant for PCI due to catheter thrombosis risk 1, 4
For Post-Fibrinolytic PCI
- Continue UFH through PCI with additional boluses as needed for therapeutic ACT 4
- Enoxaparin: No additional dose if last dose within 8 hours; 0.3 mg/kg IV bolus if last dose 8-12 hours earlier 1, 4
Statin Loading Doses
The guidelines do not specify a loading dose for statins in acute MI. While high-intensity statin therapy should be initiated early (ideally within 24 hours), the evidence focuses on early initiation rather than loading doses. Standard dosing of high-intensity statins (e.g., atorvastatin 80 mg daily) should begin promptly 5.
Key Clinical Considerations
Timing is critical: Aspirin should be given immediately upon presentation. P2Y12 inhibitors should be administered "as early as possible" - ideally before or at the time of PCI, not delayed until after angiography 1, 2.
Prasugrel-specific warnings:
- Absolute contraindication: Prior stroke/TIA
- Use caution in patients ≥75 years (consider 5 mg maintenance dose)
- Use caution in patients <60 kg body weight (consider 5 mg maintenance dose) 1, 3, 2
Ticagrelor-specific requirement: When using ticagrelor, aspirin maintenance dose must be ≤100 mg daily (preferably 81 mg) for optimal efficacy 1, 2
Common pitfall: Do not give prasugrel <24 hours after fibrin-specific fibrinolytic or <48 hours after non-fibrin-specific fibrinolytic 4