What are the treatment options and dosages for myocardial infarction?

Treatment Options and Dosages for Myocardial Infarction

The primary treatment for myocardial infarction includes immediate administration of aspirin (162-325 mg loading dose), reperfusion therapy (either fibrinolysis or primary PCI), antiplatelet therapy, anticoagulation, and supportive care based on the type of MI and patient characteristics. 1

Initial Emergency Management

• Administer oxygen via nasal prongs to maintain adequate oxygenation, especially for patients who are breathless 1, 2
• Provide sublingual nitroglycerin unless systolic blood pressure is <90 mmHg or heart rate is <50 or >100 beats per minute 1
• Administer adequate analgesia with morphine sulfate or meperidine to relieve pain and reduce myocardial oxygen demand 1, 3
• Give aspirin 162-325 mg orally as a loading dose immediately 1
• Perform 12-lead ECG within 10 minutes of arrival to identify ST-segment elevation or new LBBB, which would indicate candidacy for immediate reperfusion therapy 1

Reperfusion Therapy

Fibrinolytic Therapy

• Initiate within 12 hours of symptom onset, with greatest benefit when given within 6 hours 1
• Options include:
  • Tissue plasminogen activator (tPA)
  • Streptokinase
  • Urokinase 3
• Contraindicated in patients with history of intracranial hemorrhage, recent stroke, or active bleeding 1

Primary Percutaneous Coronary Intervention (PCI)

• Preferred over fibrinolysis when performed by skilled operators within 90 minutes of first medical contact 1
• Requires access to emergency coronary artery bypass graft (CABG) surgery 1
• Urgent CABG indicated for patients with STEMI and coronary anatomy not amenable to PCI who have ongoing ischemia, cardiogenic shock, severe heart failure, or other high-risk features 1

Antiplatelet Therapy

Aspirin

• Initial loading dose: 162-325 mg 1
• Maintenance dose: 81-325 mg daily indefinitely, with 81 mg preferred 1
• If true aspirin allergy exists, use clopidogrel 75 mg daily or ticlopidine 250 mg twice daily 1

P2Y12 Inhibitors

• Clopidogrel:
  • For patients undergoing PCI within 24 hours after fibrinolytic therapy: 300 mg loading dose 1
  • For patients undergoing PCI more than 24 hours after fibrinolytic therapy: 600 mg loading dose 1
  • Maintenance dose: 75 mg daily 1
• Prasugrel:
  • Loading dose: 60 mg (only if PCI is performed >24 hours after fibrin-specific agent or >48 hours after non-fibrin-specific agent) 1
  • Maintenance dose: 10 mg daily 1
  • Contraindicated in patients with prior stroke or TIA 1

Anticoagulation Therapy

• Unfractionated heparin (UFH):
  • Continue through PCI, administering additional IV boluses as needed to maintain therapeutic ACT 1
• Enoxaparin:
  • Continue through PCI 1
  • No additional drug if last dose was within previous 8 hours 1
  • 0.3 mg/kg IV bolus if last dose was 8-12 hours earlier 1
• Fondaparinux should not be used as the sole anticoagulant for PCI due to risk of catheter thrombosis 1

Beta-Blockers

• For early treatment of MI:
  • Begin with three bolus injections of 5 mg metoprolol IV at approximately 2-minute intervals 4
  • For patients who tolerate the full IV dose, initiate metoprolol tablets 50 mg every 6 hours, 15 minutes after the last IV dose and continue for 48 hours 4
  • Maintenance dose: 100 mg orally twice daily 4
  • For patients with intolerance, start with 25 mg or 50 mg every 6 hours depending on the degree of intolerance 4
• Monitor blood pressure, heart rate, and ECG during administration 4

ACE Inhibitors

• For acute MI:
  • Lisinopril: Start with 5 mg within 24 hours of symptom onset, 5 mg after 24 hours, then 10 mg daily 5
  • For patients with systolic BP <120 mmHg, start with 2.5 mg 5
  • Reduce dose or discontinue if severe hypotension occurs 5

Duration of Therapy

• Aspirin: Indefinitely 1
• P2Y12 inhibitors:
  • With drug-eluting stent (DES): At least 1 year 1
  • With bare-metal stent (BMS): At least 30 days and up to 1 year 1

Special Considerations

• Avoid ibuprofen as it blocks the antiplatelet effects of aspirin 1
• For patients with RV infarction, aggressive volume resuscitation is essential to maintain adequate preload 6
• Avoid nitrates in patients with RV infarction as they can cause profound hypotension 6
• Consider temporary pacing for symptomatic high-degree AV block, especially if unresponsive to atropine 6
• Monitor for mechanical complications of MI, which may worsen the clinical picture 6

Common Pitfalls to Avoid

• Delaying aspirin administration while waiting for definitive diagnosis 2
• Using fondaparinux as the sole anticoagulant during PCI 1
• Administering prasugrel to patients with history of stroke or TIA 1
• Underestimating the importance of blood pressure control in preventing recurrence 2
• Using beta-blockers in patients with hemorrhagic shock, as they may worsen hypotension 6