Why is Enoxaparin (low molecular weight heparin) preferred over Dalteparin (low molecular weight heparin) for treating Myocardial Infarction (MI)?

Enoxaparin vs Dalteparin for Myocardial Infarction Treatment

Enoxaparin is preferred over dalteparin for treating myocardial infarction due to its superior efficacy in reducing death, recurrent MI, and need for urgent revascularization, as demonstrated in multiple clinical trials. 1

Pharmacological Differences

The preference for enoxaparin over dalteparin can be explained by several key pharmacological differences:

• Anti-Xa:Anti-IIa ratio: Enoxaparin has a higher anti-Xa:anti-IIa ratio (3-4:1) compared to dalteparin (~2.2:1), which may contribute to its superior clinical efficacy 1
• Molecular structure: Both are low molecular weight heparins (LMWHs) but have different molecular compositions affecting their binding properties and bioavailability

Evidence Supporting Enoxaparin's Superiority

Clinical Trial Evidence

• The ESSENCE trial demonstrated that enoxaparin was significantly more effective than unfractionated heparin (UFH) with a 15% risk reduction in death, MI, or recurrent angina at 30 days (19.8% vs 23.3%, p=0.016) 2
• TIMI-11B showed an 18% relative risk reduction in events at 14 days (p=0.029) and a 12% risk reduction at 43 days (p=0.048) with enoxaparin compared to UFH 2
• The ExTRACT-TIMI 25 trial showed enoxaparin significantly reduced the 30-day combined incidence of all-cause mortality plus recurrent nonfatal MI compared to UFH, with benefits maintained at 1-year follow-up 3

Comparative Studies

• The ARMADA study directly compared enoxaparin, dalteparin, and UFH in patients with unstable angina or NSTEMI and found that enoxaparin had more favorable effects on key markers of blood cell activation, particularly glycoprotein Ib/IX complexes 4
• The composite clinical endpoint (death, MI, recurrent ischemia) occurred in 13% of patients with enoxaparin, 19% with dalteparin, and 28% with UFH 4

Dalteparin's Performance

• In the FRIC study (Fragmin In unstable Coronary disease), dalteparin showed no superiority over UFH in preventing death, MI, or recurrent angina at 6 days (9.3% vs 7.6%) or at 45 days (12.3% in both groups) 2
• While dalteparin did reduce left ventricular thrombus formation in anterior MI patients in the FRAMI study, it was associated with significantly increased bleeding risk 2

Safety Considerations

• Bleeding risk: Both LMWHs carry bleeding risks, but their safety profiles differ:

  • Enoxaparin has similar major bleeding rates compared to UFH in the acute phase but may have higher minor bleeding rates 1
  • Dalteparin showed significantly higher rates of both major (2.9% vs 0.3%, p=0.006) and minor bleeding (14.8% vs 1.8%, p<0.001) compared to placebo in the FRAMI study 2

• Special populations: Dose adjustments are recommended for enoxaparin in:

  • Patients ≥75 years old (no initial bolus, reduced maintenance dose)
  • Patients with severe renal insufficiency
  • Low body weight patients 1

Clinical Application

For ST-elevation myocardial infarction (STEMI):

• Primary PCI is preferred if available within 90 minutes
• If thrombolytics are used, enoxaparin is preferred with the following dosing:
  • 30 mg IV bolus followed by 1 mg/kg SC every 12 hours
  • For patients ≥75 years: omit bolus and reduce to 0.75 mg/kg SC every 12 hours 1

For non-ST-elevation acute coronary syndrome (NSTE-ACS):

• Enoxaparin (1 mg/kg SC every 12 hours) is recommended as first-line therapy
• Dalteparin (120 U/kg SC every 12 hours) may be considered as an alternative 1

Conclusion

The evidence clearly supports enoxaparin as the preferred LMWH for treating myocardial infarction based on superior efficacy outcomes and a favorable safety profile compared to dalteparin. The higher anti-Xa:anti-IIa ratio of enoxaparin likely contributes to its enhanced antithrombotic effects while maintaining an acceptable bleeding risk profile.