What is the typical dose for a heparin (unfractionated heparin) bolus?

Heparin Bolus Dosing

For acute myocardial infarction (MI), administer an initial intravenous bolus of 60 U/kg (maximum 4,000-5,000 units) followed by a continuous infusion of 12 U/kg/hour, targeting an aPTT of 50-70 seconds. 1

Context-Specific Dosing Recommendations

ST-Elevation Myocardial Infarction (STEMI)

Primary PCI without GP IIb/IIIa inhibitors:

• Initial bolus: 100 U/kg (or 70-100 U/kg weight-adjusted) 2
• Target ACT: 250-350 seconds 2
• Additional boluses may be given to maintain therapeutic ACT 2

Primary PCI with GP IIb/IIIa inhibitors:

• Initial bolus: 60 U/kg 2
• Target ACT: 200-250 seconds 2
• Lower dosing reduces bleeding risk when combined with platelet inhibitors 2, 3

With fibrinolytic therapy (alteplase):

• Initial bolus: 60 U/kg (maximum 4,000 units) 1
• Followed by 12 U/kg/hour infusion (maximum 1,000 U/hour) 1
• Target aPTT: 50-70 seconds 1

Non-ST-Elevation MI and Unstable Angina

• Initial bolus: 60-70 U/kg (maximum 5,000 units) 1
• Followed by 12-15 U/kg/hour continuous infusion 1
• Target aPTT: 50-70 seconds (1.5-2.5 times control) 2, 1

Venous Thromboembolism (for comparison)

• Initial bolus: 80 U/kg 2, 4, 5
• Followed by 18 U/kg/hour infusion 2, 4, 5
• Target aPTT: 1.5-2.5 times control (typically 45-75 seconds) 4

Critical Timing Considerations

Achieving therapeutic anticoagulation rapidly is essential:

• Patients who reach therapeutic aPTT within 24 hours have significantly lower mortality rates in pulmonary embolism 2, 4
• Weight-based dosing achieves therapeutic levels faster than fixed-dose regimens (97% vs 77% within 24 hours) 5
• Subtherapeutic anticoagulation in the first 24 hours increases recurrent thromboembolism risk to 25% 6

Monitoring Protocol

Initial monitoring:

• First aPTT check: 4-6 hours after bolus for continuous infusion 7
• First aPTT check: 3 hours after bolus for VTE treatment 2
• ACT monitoring during PCI: maintain target throughout procedure 2

Ongoing monitoring:

• aPTT every 6 hours until therapeutic, then daily 7, 5
• Platelet counts periodically throughout therapy 7
• Hematocrit and occult blood in stool 7

Common Pitfalls to Avoid

Fixed-dose regimens are inferior:

• Standard 5,000-unit bolus followed by 1,000 U/hour results in higher recurrent thromboembolism rates (relative risk 5.0) 5
• Weight-based dosing is superior and should always be used when patient weight is available 2, 5

Excessive anticoagulation with combination therapy:

• When combining heparin with GP IIb/IIIa inhibitors, reduce bolus to 60 U/kg to avoid bleeding complications 2, 3
• Bleeding rates increase from 3.9% to 16.4% with conventional higher dosing 3

Inadequate initial dosing:

• Failure to achieve therapeutic anticoagulation within 24 hours dramatically increases adverse outcomes 2, 4
• Do not use enteric-coated aspirin concurrently due to slow onset 2

Special Populations

Pediatric patients (cardiac catheterization):

• Initial bolus: 100-150 U/kg 2
• Target ACT: >200 seconds (250-300 seconds for high-risk procedures) 2
• A 50 U/kg bolus is insufficient and not recommended 2

Cardiovascular surgery:

• Initial dose: minimum 150 U/kg 7
• 300 U/kg for procedures <60 minutes 7
• 400 U/kg for procedures >60 minutes 7