What are the initial medications and dosages for a patient with suspected acute coronary syndrome?

Initial Medications and Dosages for Suspected Acute Coronary Syndrome

For any patient with suspected ACS, immediately administer aspirin 162-325 mg orally (chewed, non-enteric coated) as soon as possible, followed by a maintenance dose of 75-100 mg daily. 1

Immediate Antiplatelet Therapy

Aspirin (First-Line, Class I Recommendation)

• Loading dose: 162-325 mg orally, chewed (non-enteric coated) for faster absorption 1
• Alternative routes: Rectal or intravenous (where available) if patient cannot take oral medication 1
• Maintenance dose: 75-100 mg daily (non-enteric coated) 1
• Timing: Administer immediately upon presentation, regardless of whether invasive or conservative strategy is planned 1
• Evidence: Aspirin alone reduces 35-day mortality by 23% relative risk reduction (2.4% absolute benefit) in acute MI 2

P2Y12 Inhibitor (Add to Aspirin for Dual Antiplatelet Therapy)

For patients proceeding to PCI, prasugrel is preferred over ticagrelor 1:

• Prasugrel: 60 mg loading dose, then 10 mg daily (5 mg daily if age >75 years or weight <60 kg) 1
• Ticagrelor: 180 mg loading dose, then 90 mg twice daily (can be used regardless of invasive vs. conservative strategy) 1
• Clopidogrel: 300-600 mg loading dose, then 75 mg daily—only when prasugrel or ticagrelor are unavailable, not tolerated, or contraindicated 1, 3

Critical caveat: Do NOT routinely pre-treat with P2Y12 inhibitors before coronary anatomy is known if early invasive management is planned (Class III recommendation) 1. However, pre-treatment may be considered in patients not planned for early invasive strategy and without high bleeding risk 1.

Anticoagulation (Parenteral)

Initiate parenteral anticoagulation immediately for all patients 1:

• Unfractionated heparin (UFH): Weight-adjusted IV bolus of 70-100 IU/kg during PCI (50-70 IU/kg if combined with GP IIb/IIIa inhibitor); target activated clotting time 250-350 seconds 1
• Enoxaparin: Preferred alternative to UFH, particularly if medical management or logistical delays to PCI 1
• Fondaparinux: Recommended if medical treatment or transfer delays; give single UFH bolus at time of PCI 1
• Bivalirudin: May be considered as alternative to UFH 1

Do NOT crossover between UFH and low-molecular-weight heparin (Class III recommendation) 1.

Symptom Management

Nitroglycerin

• Sublingual: 0.4 mg every 5 minutes up to 3 doses for persistent chest pain 1
• Intravenous: Consider for persistent anginal pain after oral nitrates, or if ACS accompanied by hypertension or pulmonary edema 1
• Contraindications: Do NOT give if systolic BP <90 mmHg, >30 mmHg drop from baseline, suspected right ventricular infarction, or recent phosphodiesterase-5 inhibitor use (within 12 hours of avanafil, 24 hours of sildenafil/vardenafil, 48 hours of tadalafil) 1

Opioid Analgesia (Use Judiciously)

• Morphine: 2-4 mg IV, may repeat every 5-15 minutes (up to 10 mg) for pain resistant to maximally tolerated anti-ischemic medications 1
• Fentanyl: 25-50 μg IV, may repeat (up to 100 μg) 1
• Important warning: Opioids may delay absorption and pharmacodynamic effects of oral P2Y12 inhibitors 1. Do NOT use opioids solely to mask ongoing ischemic symptoms—pursue rapid revascularization instead 1

Beta-Blockers

Initiate within 24 hours unless contraindications exist 2:

• Metoprolol: IV administration of three 5 mg boluses at 2-minute intervals, followed by 50 mg orally every 6 hours for 48 hours, then 100 mg twice daily 4
• Contraindications: Heart failure, low-output state, risk of cardiogenic shock, hemodynamic instability 2

Critical Pitfalls to Avoid

• Do NOT use nonsteroidal anti-inflammatory drugs (NSAIDs) other than aspirin for chest pain—associated with increased MACE without documented benefit 1
• Do NOT delay reperfusion for consultation—delays increase mortality 5
• Do NOT give GP IIb/IIIa antagonists routinely before coronary anatomy is known (Class III recommendation) 1
• Recognize atypical presentations: Women and elderly frequently present with dyspnea, fatigue, or nausea rather than chest pain 5
• Balance bleeding risk: Particularly in elderly patients or those with renal impairment when selecting antithrombotic regimens 5

Timing and Monitoring

• ECG within 10 minutes of presentation to differentiate STEMI from NSTE-ACS 5
• Troponin measurements: At presentation and repeated at 6-12 hours 2
• Continuous multi-lead ECG monitoring for arrhythmias and recurrent ischemia 1
• Discontinue parenteral anticoagulation immediately after invasive procedure 1