What is the role of injectable enoxaparin (low molecular weight heparin) in patients with ST elevation myocardial infarction (STEMI)?

Role of Injectable Enoxaparin in ST Elevation Myocardial Infarction

Enoxaparin is the preferred anticoagulant over unfractionated heparin (UFH) in STEMI patients receiving fibrinolytic therapy, and should be administered as an adjunctive therapy to reduce mortality and reinfarction risk. 1

Indications for Enoxaparin in STEMI

Enoxaparin is indicated in STEMI patients in the following scenarios:

1. With fibrinolytic therapy:

   • Class I, Level A recommendation as the preferred anticoagulant over UFH 1
   • Should be administered until revascularization (if performed) or for the duration of hospital stay up to 8 days 1

2. For primary PCI:

   • When used for primary PCI, additional considerations are needed
   • For patients previously on subcutaneous enoxaparin, an additional 0.3 mg/kg IV dose should be administered if the last dose was 8-12 hours before PCI 1

3. For patients not receiving reperfusion therapy:

   • Enoxaparin is superior to placebo and UFH in reducing death and reinfarction 1

Dosing Recommendations

For Fibrinolytic Therapy

• Patients <75 years old: 30 mg IV bolus followed by 1 mg/kg SC every 12 hours (first SC dose shortly after IV bolus) 2
• Patients ≥75 years old: 0.75 mg/kg SC every 12 hours without initial IV bolus 2
• Impaired renal function (CrCl <30 mL/min): 1 mg/kg SC once daily 2
• Continue until revascularization or hospital discharge (maximum 8 days) 1

For Primary PCI

• If patient received subcutaneous enoxaparin <8 hours before PCI: No additional anticoagulation needed 1
• If 8-12 hours since last subcutaneous dose: Additional 0.3 mg/kg IV bolus at time of PCI 1
• If no prior antithrombin therapy: Consider 0.5-0.75 mg/kg IV at time of PCI 1, 3

Clinical Evidence

The ExTRACT-TIMI 25 study demonstrated that enoxaparin was superior to UFH in STEMI patients receiving fibrinolytic therapy:

• Primary endpoint of death or nonfatal recurrent MI at 30 days: 9.9% with enoxaparin vs. 12.0% with UFH 1, 4
• Net clinical benefit (death, MI complications, or major bleeding): 10% with enoxaparin vs. 15% with UFH (P=0.03) 1

For primary PCI, studies have shown that enoxaparin is associated with:

• Reduction in all ischemic complications compared to UFH 5
• More frequent therapeutic anticoagulation (68% vs. 50%, P<0.0001) 5
• No significant increase in major bleeding events 5

Important Considerations and Pitfalls

1. Do not switch between enoxaparin and UFH during treatment due to increased bleeding risk 2

2. Do not use fondaparinux alone for primary PCI due to risk of catheter thrombosis 1

3. Bleeding risk considerations:

   • Enoxaparin may be associated with increased bleeding risk compared to UFH (2.1% vs. 1.4% in ExTRACT-TIMI 25) 1
   • Consider reduced dosing in elderly patients and those with renal impairment 2

4. Catheter thrombosis risk:

   • When using subcutaneous enoxaparin before primary PCI, consider supplementary IV enoxaparin to ensure adequate anticoagulation 6
   • Anti-Xa activity should be at target level (>0.5 IU/ml) during PCI 3

5. Timing of administration:

   • For fibrinolytic therapy, start anticoagulation as soon as possible after STEMI diagnosis 1
   • For primary PCI, ensure proper timing of doses relative to the procedure 1

By following these evidence-based recommendations, enoxaparin can effectively reduce mortality and reinfarction risk in STEMI patients while maintaining an acceptable safety profile.