What is the recommended heparin (unfractionated heparin) dosing for a patient with Non-ST-Elevation Myocardial Infarction (NSTEMI)?

Unfractionated Heparin Dosing for NSTEMI

For patients with Non-ST-Elevation Myocardial Infarction (NSTEMI), the recommended unfractionated heparin (UFH) dosing is an initial bolus of 60 U/kg (maximum 4,000 U) followed by an infusion of 12 U/kg/hour (maximum 1,000 U/hour), with dose adjustments to maintain activated partial thromboplastin time (aPTT) at 1.5 to 2.0 times control (approximately 50 to 70 seconds). 1

Initial Dosing Recommendations

• The loading dose (bolus) should be 60 U/kg (maximum 4,000 U) administered intravenously 1
• The maintenance dose should be an IV infusion of 12 U/kg/hour (maximum 1,000 U/hour) 1
• Target aPTT should be 1.5 to 2.0 times control (approximately 50 to 70 seconds) 1
• The available data do not suggest a benefit of prolonging the duration of the UFH infusion beyond 48 hours in the absence of ongoing indications for anticoagulation 1

Dosing Considerations During PCI

For NSTEMI patients who will undergo percutaneous coronary intervention (PCI), the UFH dosing depends on whether glycoprotein (GP) IIb/IIIa inhibitors are planned:

• If GP IIb/IIIa inhibitors are planned: target activated clotting time (ACT) of 200 seconds 1
• If no GP IIb/IIIa inhibitors are planned: target ACT of 250-300 seconds for HemoTec device or 300-350 seconds for Hemochron device 1

Monitoring and Dose Adjustment

• Frequent monitoring of aPTT is essential to ensure therapeutic anticoagulation while minimizing bleeding risk 1
• Excess dosing (>70 U/kg for bolus or >15 U/kg/hour for infusion) is associated with increased risk of major bleeding 1, 2
• Studies show that standard dosing protocols may lead to subtherapeutic anticoagulation, particularly in obese patients 3
• Only 23% of patients achieve therapeutic aPTT values within 6 hours even with higher dosing strategies, suggesting careful monitoring and adjustment are critical 3

Special Considerations

• Elderly patients and females are at higher risk of receiving excess weight-adjusted dosing, which increases bleeding risk 2
• For patients with renal insufficiency, standard UFH is preferred over low molecular weight heparin as it does not require dose adjustment for renal function 4
• Patients who have already received one form of anticoagulant (e.g., enoxaparin) should not be given additional UFH to avoid increased bleeding risk 1, 5

Alternative Anticoagulation Options

If UFH is contraindicated or not preferred, other anticoagulation options for NSTEMI include:

• Enoxaparin: 1 mg/kg subcutaneously every 12 hours (maximum 10,000 IU twice daily) 1, 6
• Bivalirudin: 0.1 mg/kg bolus, followed by 0.25 mg/kg/hour infusion 1
• Fondaparinux: 2.5 mg subcutaneously once daily 1

Common Pitfalls to Avoid

• Using fixed-dose regimens rather than weight-based dosing can lead to subtherapeutic anticoagulation in larger patients and excessive anticoagulation in smaller patients 2
• Switching between different anticoagulants during the same admission increases bleeding risk 1, 5
• Failure to adjust dosing based on renal function can lead to accumulation and increased bleeding risk 4
• Excessive dosing is common and associated with increased bleeding, particularly in elderly patients and women 2

Conclusion

The optimal UFH dosing strategy for NSTEMI balances the need for adequate anticoagulation with minimizing bleeding risk. Weight-based dosing with careful monitoring and adjustment is essential for achieving this balance.