UFH Dosing for Myocardial Infarction
For patients with MI, administer unfractionated heparin as a weight-adjusted bolus of 60 U/kg (maximum 4000 U) followed by an infusion of 12 U/kg/hour (maximum 1000 U/hour), adjusted to maintain aPTT at 1.5-2.0 times control (50-70 seconds). 1
Dosing Regimen by Clinical Scenario
STEMI with Fibrin-Specific Thrombolytics (Alteplase, Reteplase, Tenecteplase)
- Initial bolus: 60 U/kg IV (maximum 4000 U) 1
- Initial infusion: 12 U/kg/hour (maximum 1000 U/hour) 1
- Target aPTT: 1.5-2.0 times control (approximately 50-70 seconds) 1
- Duration: 48 hours, then discontinue unless high risk for systemic/venous thromboembolism 1
- Monitoring: Check aPTT at 3,6,12, and 24 hours 1
The weight-adjusted approach is critical because traditional fixed-dose regimens (5000 U bolus, 1000 U/hour infusion) result in unpredictable anticoagulation and frequently lead to excessive initial anticoagulation, particularly in lighter patients. 1, 2
STEMI with Non-Selective Fibrinolytics (Streptokinase, Anistreplase, Urokinase)
- Timing: Withhold heparin for 4 hours after thrombolytic administration 1
- Initiation: Start when aPTT returns to <2 times control (<70 seconds) 1
- Dosing: Same weight-adjusted regimen as above (60 U/kg bolus, 12 U/kg/hour infusion) 1
- High-risk patients only: Those with large or anterior MI, atrial fibrillation, previous embolus, or known LV thrombus 1
NSTEMI/Unstable Angina (Without Fibrinolytics)
- Initial bolus: 60-70 U/kg IV (maximum 4000-5000 U) 1, 3
- Initial infusion: 12-15 U/kg/hour (maximum 1000 U/hour) 1, 3
- Target aPTT: 1.5-2.0 times control (50-70 seconds) 1
The slightly higher dosing range (up to 70 U/kg bolus and 15 U/kg/hour infusion) for NSTEMI reflects ACC/AHA UA/NSTEMI guideline recommendations, though the lower end of this range is equally acceptable. 1, 3
Primary PCI (Without Fibrinolytics)
- Without GP IIb/IIIa inhibitors: 70-100 U/kg IV bolus 1
- With GP IIb/IIIa inhibitors: 50-60 U/kg IV bolus 1
- Additional boluses: Administer as needed during procedure, accounting for GP IIb/IIIa use 1
Critical Dosing Caveats
Maximum Dose Caps Are Essential
Never exceed 4000 U bolus or 1000 U/hour initial infusion in patients >70 kg. 1 These caps prevent excessive anticoagulation, which is associated with increased bleeding, intracranial hemorrhage, reinfarction, and death. 1, 2 Registry data demonstrate that overdosing is common in clinical practice, making adherence to these maximums a quality measure. 1
Weight-Based Dosing Is Non-Negotiable
Body weight is the strongest predictor of heparin effect on aPTT. 3, 2 Fixed-dose regimens result in 95% of patients being above target aPTT at 6 hours, while weight-adjusted dosing achieves therapeutic range in only 23-34% at 6 hours—still suboptimal but significantly better. 4, 2 Calculate actual body weight in kilograms before administration. 1
Duration Limitations
Do not continue UFH infusion beyond 48 hours unless ongoing indications exist (high embolic risk, recurrent ischemia). 1 Prolonged infusions increase risk of heparin-induced thrombocytopenia without additional benefit. 1
Monitoring Requirements
- Daily platelet counts to detect heparin-induced thrombocytopenia 1
- Serial aPTT measurements at 3,6,12, and 24 hours to guide dose adjustments 1
- Adjust infusion rate to maintain aPTT 1.5-2.0 times control 1
Special Populations
Obese Patients
Standard weight-based dosing with maximum caps applies equally to obese and non-obese patients. 4 However, obese patients in particular are prone to subtherapeutic anticoagulation with standard dosing, and some evidence suggests even higher maximum infusion rates (up to 2250 U/hour) may be safe and more effective, though this exceeds current guideline recommendations. 4
Patients Already on Anticoagulation
Exclude patients who received enoxaparin, bivalirudin, or fondaparinux prior to UFH from standard dosing protocols. 1 For patients already on UFH who require PCI, give additional boluses as needed rather than restarting the full regimen. 1