UFH Infusion Dosing
For acute coronary syndromes, administer an initial bolus of 60 U/kg (maximum 4,000 units) followed by an infusion of 12 U/kg/hour (maximum 1,000 units/hour), adjusted to maintain aPTT at 1.5-2.0 times control (50-70 seconds). 1
Initial Dosing by Clinical Indication
Acute Coronary Syndromes (STEMI/NSTEMI)
- Bolus: 60 U/kg IV (maximum 4,000 units) 1, 2
- Infusion: 12 U/kg/hour (maximum 1,000 units/hour) 1, 2
- Target aPTT: 1.5-2.0 times control (approximately 50-70 seconds) 1
- Duration: 48 hours, then discontinue unless high risk for systemic or venous thromboembolism 1
PCI Support (No Prior Anticoagulation)
- Bolus: 70-100 U/kg IV to achieve target ACT of 250-300 seconds 1
- If using concomitant glycoprotein IIb/IIIa inhibitors, reduce bolus to 60 U/kg (maximum 4,000 units) and target ACT of 200-250 seconds 1
Venous Thromboembolism
Atrial Fibrillation/Flutter
- No bolus recommended 3
- Infusion: 9.7-11.0 U/kg/hour (lower than ACS dosing) 3
- Initial rates >11.0 U/kg/hour are associated with increased bleeding risk (OR 1.95) without improved therapeutic efficacy 3
Critical Dosing Caveats
Maximum Dose Caps
- Never exceed 4,000 units for initial bolus in patients >70 kg 1
- Never exceed 1,000 units/hour for initial infusion in ACS patients >70 kg 1
- Exceeding these caps significantly increases bleeding risk, particularly in elderly patients and women 4
Weight-Based Dosing is Mandatory
- Fixed-dose regimens (e.g., 5,000 unit bolus, 1,000 units/hour infusion) result in subtherapeutic anticoagulation in 70.8% of patients at 6 hours 5
- Body weight is the strongest predictor of heparin effect on aPTT 5
- Excess weight-adjusted dosing occurs in 35% of patients, particularly in elderly and female patients with lower body weight 4
Obesity Considerations
- Standard protocols with maximum dose caps cause significant delays in achieving therapeutic anticoagulation in obese patients 6, 7
- For morbidly obese patients (BMI >40), consider using adjusted body weight: dosing weight = IBW + 0.3(ABW - IBW) or IBW + 0.4(ABW - IBW) 6
- Higher maximum infusion rates (up to 2,250 units/hour) achieve therapeutic aPTT more rapidly in obese patients without increased bleeding 7
Monitoring Requirements
aPTT Monitoring Schedule
- Initial: Check aPTT at 3,6,12, and 24 hours after starting infusion 1, 2
- After dose adjustments: Check aPTT 4-6 hours after any rate change 2
- Ongoing: Continue monitoring at appropriate intervals to maintain therapeutic range 2
Platelet Monitoring
- Check daily platelet counts throughout entire course of therapy to detect heparin-induced thrombocytopenia 1, 2
Additional Safety Monitoring
- Monitor hematocrit and occult blood in stool periodically 2
- For subcutaneous dosing, draw aPTT samples 4-6 hours after injection 2
Common Pitfalls to Avoid
Premature Discontinuation
- Do not stop heparin before 48 hours in ACS patients without clear clinical justification 1
- Prolonged infusions beyond 48 hours increase risk of heparin-induced thrombocytopenia without additional benefit 1
Bolus Administration in Atrial Fibrillation
- Bolus dosing in AF/AFL patients does not improve time to therapeutic aPTT (56.1% vs 56.3%) and does not significantly increase bleeding (35.7% vs 31.3%) 3
- However, boluses are unnecessary in this population and should be avoided 3
Concurrent Anticoagulation
- Exclude patients already receiving enoxaparin, bivalirudin, or fondaparinux from standard UFH protocols 1
- For patients on enoxaparin requiring PCI: if last dose was 8-12 hours prior, give 0.3 mg enoxaparin IV; if within 8 hours, give no additional anticoagulation 1
Excessive Dosing Recognition
- Excessive bolus: >70 U/kg or total dose >4,000 units 1
- Excessive infusion: >15 U/kg/hour or total rate >1,000 units/hour (for ACS) 1
- Both excess bolus (OR 1.03) and infusion (OR 1.16) independently increase major bleeding risk 4