What are the recommended loading doses of antiplatelet and anticoagulant agents for a patient presenting with ST-elevation myocardial infarction (STEMI)?

Cardiac Loading Doses for STEMI

For STEMI patients undergoing primary PCI, administer aspirin 162-325 mg (chewed if possible) plus a P2Y12 inhibitor loading dose (prasugrel 60 mg or ticagrelor 180 mg preferred; clopidogrel 600 mg if others unavailable), along with anticoagulation using either unfractionated heparin (UFH) or bivalirudin.

Antiplatelet Therapy

Aspirin Loading

• Loading dose: 162-325 mg orally before primary PCI 1, 2, 3
• Aspirin should be chewed (non-enteric coated) when possible to achieve faster onset of antiplatelet action 3
• Administer even if patient is already on aspirin therapy 3
• Maintenance: 75-100 mg daily (preferred) or 81-325 mg daily indefinitely after PCI 1, 2, 3
• The 75-100 mg daily dose is preferred for maintenance to reduce bleeding risk while maintaining efficacy 1, 2, 3

P2Y12 Inhibitor Loading (Primary PCI)

Three options exist, with prasugrel and ticagrelor preferred over clopidogrel:

Prasugrel (Preferred for Primary PCI)

• Loading dose: 60 mg orally as early as possible or at time of PCI 1, 2, 3
• Maintenance: 10 mg daily (5 mg daily if age ≥75 years or body weight <60 kg) 1, 2, 3
• Contraindication: History of prior stroke or TIA 1, 4, 3
• Prasugrel provides faster onset and superior effectiveness compared to clopidogrel in STEMI 5

Ticagrelor (Preferred for Primary PCI)

• Loading dose: 180 mg orally as early as possible or at time of PCI 1, 2, 3
• Maintenance: 90 mg twice daily 1, 2, 3
• Important: Aspirin maintenance dose must be ≤100 mg daily when using ticagrelor 1, 2, 3

Clopidogrel (Alternative)

• Loading dose: 600 mg orally as early as possible or at time of PCI 1, 2, 3
• Use when prasugrel or ticagrelor are unavailable, not tolerated, or contraindicated 3
• Maintenance: 75 mg daily 1, 2
• The 600 mg loading dose is superior to 300 mg, reducing infarct size, improving TIMI flow, and decreasing 30-day major adverse cardiovascular events 6, 7, 8

Anticoagulation Therapy

Unfractionated Heparin (UFH)

• With GP IIb/IIIa inhibitor planned: 50-70 units/kg IV bolus to achieve ACT 200-250 seconds 1, 2
• Without GP IIb/IIIa inhibitor: 70-100 units/kg IV bolus to achieve ACT 250-350 seconds 1, 2
• Additional boluses administered as needed to maintain therapeutic ACT 1, 2

Bivalirudin (Alternative)

• 0.75 mg/kg IV bolus, then 1.75 mg/kg/hour infusion 1, 2
• Can be given with or without prior UFH treatment 1, 2
• Additional 0.3 mg/kg bolus can be given if needed 1, 2
• Preferred over UFH with GP IIb/IIIa inhibitor in patients at high bleeding risk 1, 2
• Reduce infusion to 1 mg/kg/hour if creatinine clearance <30 mL/min 1, 2

GP IIb/IIIa Inhibitors (Selected Patients)

Use is reasonable but not mandatory in selected high-risk patients:

• Abciximab: 0.25 mg/kg IV bolus, then 0.125 mcg/kg/min infusion (maximum 10 mcg/min) 1, 2
• Tirofiban (high-bolus): 25 mcg/kg IV bolus, then 0.15 mcg/kg/min (reduce by 50% if CrCl <30 mL/min) 1, 2
• Eptifibatide (double bolus): 180 mcg/kg IV bolus, then 2 mcg/kg/min; second 180 mcg/kg bolus at 10 minutes (reduce by 50% if CrCl <50 mL/min; avoid in hemodialysis) 1, 2
• Pre-catheterization laboratory administration may be considered but is not strongly recommended 1

Special Considerations for Fibrinolytic Therapy

If primary PCI cannot be performed within 120 minutes of first medical contact:

Antiplatelet Therapy with Fibrinolysis

• Aspirin: 162-325 mg loading dose given with fibrinolytic agent 4, 9
• Clopidogrel: 300 mg loading dose if age ≤75 years; 75 mg if age >75 years 4, 9
• Clopidogrel is indicated in addition to aspirin with fibrinolytic therapy 9

Anticoagulation with Fibrinolysis

• Enoxaparin IV followed by subcutaneous (preferred over UFH) 9
• UFH: weight-adjusted IV bolus followed by infusion 9
• Continue anticoagulation until revascularization or for duration of hospital stay up to 8 days 9

Critical Pitfalls to Avoid

• Never use fondaparinux as sole anticoagulant for PCI - requires additional anticoagulant with anti-IIa activity due to catheter thrombosis risk 1, 2, 4
• Do not give prasugrel to patients with prior stroke/TIA - absolute contraindication 1, 4, 3
• Do not exceed 100 mg daily aspirin maintenance when using ticagrelor - higher doses associated with reduced ticagrelor efficacy 1, 2, 3
• Avoid 300 mg clopidogrel loading in primary PCI - 600 mg loading dose significantly reduces infarct size and improves outcomes 6, 7, 8