What are the recommended loading doses of the essential acute‑care medications for a patient presenting with an acute myocardial infarction who has no contraindications such as active bleeding, severe asthma, bradycardia, or high‑grade atrioventricular block?

Loading Doses for Acute Myocardial Infarction

For a patient presenting with acute MI without contraindications, immediately administer aspirin 162–325 mg orally (chewed, non-enteric coated), followed by a P2Y12 inhibitor loading dose (ticagrelor 180 mg preferred, or clopidogrel 300–600 mg), and initiate anticoagulation with weight-based unfractionated heparin (60 U/kg IV bolus, max 4000 U) or enoxaparin (30 mg IV bolus followed by 1 mg/kg subcutaneous every 12 hours). 1, 2

Antiplatelet Loading Doses

Aspirin

• Give 162–325 mg oral loading dose immediately to all MI patients (both STEMI and NSTEMI) as soon as possible after presentation 2, 1
• Use non-enteric coated, chewable formulation for faster buccal absorption 2, 1
• If unable to swallow, administer 250–500 mg intravenously 2, 3
• Continue with 75–100 mg daily maintenance dose (81 mg preferred when combined with ticagrelor) 2, 1

P2Y12 Inhibitors

Ticagrelor (First-Line Choice):

• 180 mg oral loading dose followed by 90 mg twice daily 2, 1
• Preferred over clopidogrel for moderate-to-high risk patients with elevated troponins 2, 1
• Can be started before coronary anatomy is known 1
• No dose adjustment needed for renal impairment 1
• Contraindications: prior intracranial hemorrhage, active bleeding 1
• Critical: Use only 81 mg daily aspirin maintenance dose with ticagrelor—higher aspirin doses diminish ticagrelor efficacy 1

Clopidogrel (Third-Line Option):

• 300–600 mg oral loading dose (600 mg preferred for faster platelet inhibition) 2, 1
• Maintenance dose: 75 mg daily 2, 1
• Use when ticagrelor or prasugrel contraindicated, or when oral anticoagulation required 1
• For patients >75 years receiving fibrinolysis: use 75 mg loading dose only (no loading dose otherwise in this age group) 1

Prasugrel (PCI-Only, After Anatomy Known):

• 60 mg oral loading dose followed by 10 mg daily (reduce to 5 mg if body weight <60 kg) 2, 1
• Must only be given AFTER coronary anatomy is known and patient is proceeding to PCI 1
• Absolute contraindications: prior stroke/TIA, age ≥75 years, body weight <60 kg, prior intracranial hemorrhage, active bleeding 1

Anticoagulation Loading Doses

Unfractionated Heparin (UFH)

• 60 U/kg IV bolus (maximum 4000 U) followed by 12 U/kg/hour infusion (maximum 1000 U/hour) 2, 1
• Adjust to therapeutic aPTT (1.5–2.0 × control) 2, 1
• Continue for at least 48 hours or until revascularization 2, 1

Enoxaparin (Preferred Over UFH)

• 30 mg IV bolus followed by 1 mg/kg subcutaneous every 12 hours 2, 1
• Dose adjustments for renal impairment:
  • CrCl <30 mL/min: 1 mg/kg every 24 hours 1
  • CrCl 30–60 mL/min: reduce dose by 25% 1
• Continue up to 8 days or until revascularization 2, 1

Bivalirudin (Alternative for Early Invasive Strategy)

• 0.10 mg/kg IV loading dose followed by 0.25 mg/kg/hour infusion 2, 1
• For CrCl <30 mL/min: use 1 mg/kg/hour infusion 1

Fondaparinux

• Initial IV dose then 2.5 mg subcutaneous daily 2, 1
• Continue up to 8 days or until revascularization 2, 1
• Contraindicated if CrCl <30 mL/min 1
• Critical: When proceeding to PCI, must add an anti-IIa anticoagulant (UFH or enoxaparin) to prevent catheter thrombosis 2, 1

Glycoprotein IIb/IIIa Inhibitors (High-Risk Patients Only)

Consider only in troponin-positive, high-risk patients undergoing early invasive strategy 2, 1

Eptifibatide:

• 180 µg/kg IV bolus (max 22.6 mg) then 2 µg/kg/min infusion 1
• If CrCl ≤50 mL/min: reduce infusion to 1.0 µg/kg/min 1

Tirofiban:

• 12 µg/kg IV bolus then 0.14 µg/kg/min infusion 1
• If CrCl <30 mL/min: use 6 µg/kg bolus plus 0.05 µg/kg/min infusion 1

Beta-Blocker Loading (If No Contraindications)

Metoprolol IV (for STEMI):

• Three 5 mg IV boluses at 2-minute intervals (total 15 mg) 4
• Monitor blood pressure, heart rate, and ECG during administration 4
• 15 minutes after last IV dose: start oral metoprolol 50 mg every 6 hours for 48 hours 4
• Then maintenance: 100 mg orally twice daily 4
• Do not give IV beta-blockers if: cardiogenic shock risk factors, severe bradycardia (<50 bpm), hypotension, heart failure 1, 4

Critical Timing Considerations

NSTEMI:

• Give aspirin and anticoagulant immediately on presentation 1
• Administer P2Y12 inhibitor as early as possible—ticagrelor may be given before coronary anatomy known, prasugrel must wait until anatomy known 1

STEMI:

• All antiplatelet and anticoagulant agents immediately after diagnosis 1
• For fibrinolytic strategy: give aspirin and clopidogrel before or together with fibrinolytic agent 1

Critical Pitfalls to Avoid

• Never give prasugrel before coronary anatomy is known—markedly raises bleeding risk if urgent CABG required 1
• Never use aspirin maintenance >100 mg with ticagrelor—higher doses diminish ticagrelor efficacy 1
• Always calculate anticoagulant doses on weight-based basis to avoid under- or overdosing 1
• Always check renal function before dosing enoxaparin, eptifibatide, or fondaparinux and apply recommended dose adjustments 1
• When fondaparinux used and patient proceeds to PCI, must add anti-IIa anticoagulant (UFH or enoxaparin) to prevent catheter thrombosis 2, 1
• Elderly patients (≥75 years) have higher bleeding risk—consider reduced clopidogrel loading dose (75 mg) with fibrinolysis and avoid prasugrel 1
• Patients with body weight <60 kg have increased bleeding risk with prasugrel—use 5 mg maintenance dose if prasugrel selected 1