What is the recommended loading dose regimen for an adult presenting with an acute ST‑elevation or non‑ST‑elevation myocardial infarction?

Loading Dose Regimens for Acute Myocardial Infarction

For adults presenting with acute MI (both STEMI and NSTEMI), administer aspirin 162-325 mg loading dose immediately, followed by a P2Y12 inhibitor: ticagrelor 180 mg (preferred), prasugrel 60 mg (only if proceeding to PCI with known anatomy), or clopidogrel 300-600 mg (if others contraindicated), plus anticoagulation with weight-based dosing. 1, 2

Antiplatelet Loading Doses

Aspirin

• Administer 162-325 mg oral loading dose immediately upon presentation to all patients with acute MI 1, 2
• If oral administration is not possible, give intravenous (250-500 mg) or rectal aspirin 2
• Continue with 75-100 mg daily maintenance dose (81 mg preferred when combined with ticagrelor) 1

P2Y12 Inhibitor Selection (in order of preference)

Ticagrelor (First-line for most patients):

• Loading dose: 180 mg orally 1, 3
• Maintenance: 90 mg twice daily 1, 3
• Recommended for all patients at moderate-to-high risk (elevated troponins), regardless of initial treatment strategy 1, 3
• Can be given to patients already on clopidogrel (discontinue clopidogrel when starting ticagrelor) 1
• No dose adjustment needed for renal impairment 3
• Contraindications: prior intracranial hemorrhage, active bleeding 1, 3

Prasugrel (Second-line, PCI-specific):

• Loading dose: 60 mg orally 1, 4
• Maintenance: 10 mg daily (5 mg if weight <60 kg) 1, 4
• Only administer AFTER coronary anatomy is known and patient is proceeding to PCI 1, 4
• Contraindications: prior stroke/TIA, age ≥75 years, weight <60 kg, prior intracranial hemorrhage, active bleeding 1, 4

Clopidogrel (Third-line alternative):

• Loading dose: 300-600 mg orally (600 mg preferred for faster platelet inhibition) 1, 2, 5
• For patients >75 years receiving fibrinolysis: 75 mg loading dose (no loading dose >75 years) 1
• Maintenance: 75 mg daily 1
• Use when ticagrelor or prasugrel contraindicated or when oral anticoagulation required 1

Anticoagulation Loading Doses

Select ONE of the following:

Unfractionated Heparin (UFH)

• Weight-based: 60 U/kg IV bolus (maximum 4000 U) 1
• Followed by 12 U/kg/h infusion (maximum 1000 U/h) 1
• Adjust to therapeutic aPTT (1.5-2.0 times control) 1
• Continue for minimum 48 hours or until revascularization 1

Enoxaparin (Low Molecular Weight Heparin)

• 30 mg IV bolus, followed in 15 minutes by 1 mg/kg subcutaneous every 12 hours 1, 2
• Dose adjustment for renal impairment: CrCl <30 mL/min: 1 mg/kg subcutaneous every 24 hours 1
• CrCl 30-60 mL/min: reduce dose by 25% 1
• Continue for duration of hospitalization, up to 8 days or until revascularization 1

Bivalirudin

• 0.75 mg/kg IV bolus 2
• Followed by 1.75 mg/kg/h infusion during PCI 2
• Alternative: 0.10 mg/kg loading dose followed by 0.25 mg/kg/h for early invasive strategy 1
• Dose adjustment for renal impairment: CrCl <30 mL/min: 1 mg/kg/h infusion 1

Fondaparinux

• Initial IV dose followed by 2.5 mg subcutaneous daily 1
• Continue for duration of hospitalization, up to 8 days or until revascularization 1
• Contraindicated if CrCl <30 mL/min 1
• Critical caveat: Must administer additional anticoagulant with anti-IIa activity (UFH or enoxaparin) if proceeding to PCI 1

Timing Considerations

NSTEMI Patients

• Aspirin and anticoagulation: immediately upon presentation 1, 2
• P2Y12 inhibitor: as early as possible 1, 2
• Ticagrelor: can be given before knowing coronary anatomy 1
• Prasugrel: wait until coronary anatomy known 1, 4

STEMI Patients

• All medications immediately upon diagnosis 1, 2
• For fibrinolysis strategy: administer aspirin and clopidogrel before or with fibrinolytic 1
• For primary PCI: administer all antiplatelet agents before catheterization when possible 2

Glycoprotein IIb/IIIa Inhibitors (Optional, High-Risk Patients)

Consider in troponin-positive, high-risk patients undergoing early invasive strategy: 1

Eptifibatide:

• 180 mcg/kg IV bolus (maximum 22.6 mg) 1, 2
• Followed by 2 mcg/kg/min infusion 1
• Dose adjustment: CrCl ≤50 mL/min: 1.0 mcg/kg/min infusion 1

Tirofiban:

• Weight-based: 12 mcg/kg IV bolus 1
• Followed by 0.14 mcg/kg/min infusion 1
• Dose adjustment: CrCl <30 mL/min: 6 mcg/kg bolus + 0.05 mcg/kg/min infusion 1

Abciximab:

• 0.25 mg/kg IV bolus 2
• Followed by 0.125 mcg/kg/min infusion (maximum 10 mg/min for 12 hours) 2
• Not recommended in elderly due to increased bleeding without benefit 1

Critical Pitfalls to Avoid

• Never give prasugrel before knowing coronary anatomy – substantial bleeding risk if urgent CABG needed 1, 4
• Do not use higher aspirin maintenance doses (>100 mg) with ticagrelor – reduces ticagrelor effectiveness 3
• Always use weight-based dosing for anticoagulants – critical to avoid underdosing and overdosing 2
• Check renal function before dosing enoxaparin, eptifibatide, fondaparinux – requires dose adjustment or contraindicated 1, 2
• Add anti-IIa anticoagulant if using fondaparinux and proceeding to PCI – prevents catheter thrombosis 1
• Elderly patients (≥75 years) have increased bleeding risk – consider lower clopidogrel loading dose (75 mg) with fibrinolysis, avoid prasugrel 1, 4
• Patients <60 kg have increased bleeding risk with prasugrel – use 5 mg maintenance dose if prasugrel selected 4