What is the recommended loading dose for a patient presenting with acute myocardial infarction (MI)?

Loading Doses for Acute Myocardial Infarction

For patients presenting with acute MI, administer aspirin 162-325 mg (chewed, non-enteric coated) immediately, followed by a P2Y12 inhibitor loading dose: ticagrelor 180 mg for NSTE-ACS or STEMI without fibrinolysis, prasugrel 60 mg for patients undergoing PCI with known coronary anatomy (if no contraindications), or clopidogrel 300-600 mg when ticagrelor or prasugrel cannot be used. 1, 2, 3

Aspirin Loading Dose

• Loading dose: 162-325 mg orally (non-enteric coated, chewed when possible for faster onset) 1, 2
• Administer as soon as possible on presentation, regardless of final management strategy (invasive or noninvasive) 1
• If oral administration is not possible, rectal or intravenous routes (where available) are alternatives 1
• Maintenance dose: 75-100 mg daily (non-enteric coated) after the loading dose 1
• When using ticagrelor, aspirin maintenance dose should be 81-100 mg daily (not higher) to avoid reducing ticagrelor's effectiveness 1, 4

P2Y12 Inhibitor Loading Doses: Algorithm for Selection

For STEMI or NSTE-ACS Undergoing Primary PCI:

First-line choice: Ticagrelor 180 mg loading dose 1, 2, 3

• Administer as soon as ACS is diagnosed 3
• Can be given to patients already pre-treated with clopidogrel (discontinue clopidogrel when starting ticagrelor) 3
• Maintenance: 90 mg twice daily 1, 4

Alternative for PCI with known coronary anatomy: Prasugrel 60 mg loading dose 1, 2, 3, 5

• Critical timing consideration: Do not administer until coronary anatomy is known in NSTE-ACS patients 5
• For STEMI presenting within 12 hours, can give at diagnosis, though most receive it at time of PCI 5
• Maintenance: 10 mg daily (or 5 mg daily if body weight <60 kg) 1, 5

Contraindications to prasugrel (use ticagrelor or clopidogrel instead):

• Prior stroke or TIA (absolute contraindication) 1, 5
• Age ≥75 years (generally not recommended except in high-risk situations like diabetes or prior MI) 1, 5
• Body weight <60 kg (use 5 mg maintenance dose if prasugrel is used) 1, 5
• Likely to undergo urgent CABG 1, 5

Third-line option: Clopidogrel loading dose 1, 2

• Use when ticagrelor or prasugrel are unavailable, contraindicated, or not tolerated 1
• For NSTE-ACS or STEMI without fibrinolytic: 300 mg or 600 mg loading dose 1
• The 600 mg dose is generally preferred for invasive strategy due to more rapid and stronger platelet inhibition 1
• Maintenance: 75 mg daily 1

For STEMI Managed with Fibrinolytic Therapy:

Clopidogrel is the recommended P2Y12 inhibitor 1

• Loading dose: 300 mg if age ≤75 years 1
• Initial dose: 75 mg (no loading dose) if age >75 years 1
• Administer concurrently with fibrinolytic therapy 1
• Maintenance: 75 mg daily 1

If PCI is performed after fibrinolytic therapy:

• If patient already received clopidogrel loading dose with fibrinolytic: continue 75 mg daily without additional loading 1
• If no prior clopidogrel loading and PCI ≤24 hours after fibrinolytic: give clopidogrel 300 mg loading dose 1
• If no prior clopidogrel loading and PCI >24 hours after fibrinolytic: give clopidogrel 600 mg loading dose 1
• Prasugrel 60 mg can be given if PCI >24 hours after fibrin-specific agent (but not <24 hours) 1, 5

Duration of Dual Antiplatelet Therapy

• Standard duration: 12 months for all ACS patients regardless of stent type or management strategy 1, 3, 4
• Continue aspirin indefinitely after 12 months 1

Critical Pitfalls to Avoid

• Do not use enteric-coated aspirin for loading dose - it has slow onset of action 2
• Do not give prasugrel to patients with prior stroke/TIA - this is an absolute contraindication due to increased risk of intracranial hemorrhage 1, 5
• Do not administer prasugrel before coronary anatomy is known in NSTE-ACS - wait until decision to proceed with PCI is made 1, 5
• Do not use aspirin >100 mg daily with ticagrelor - higher aspirin doses reduce ticagrelor's effectiveness 1, 4
• Do not discontinue DAPT prematurely, especially within the first month after stent placement - this dramatically increases thrombotic risk 3

Bleeding Risk Mitigation

• Prescribe a proton pump inhibitor (PPI) with DAPT to reduce gastrointestinal bleeding risk 2, 3
• Use radial over femoral access for coronary procedures when performed by an expert radial operator 3
• Consider clopidogrel instead of more potent P2Y12 inhibitors in patients ≥70 years with high bleeding risk 6