Heparin Dosage and Administration for Thromboembolic Disorders
For prevention and treatment of thromboembolic disorders, heparin should be administered as follows: for prophylaxis, 5000 U subcutaneously every 8-12 hours; for treatment, 5000 U IV bolus followed by 32,000 U per 24 hours by continuous IV infusion, adjusted to maintain aPTT at 1.5-2.5 times control value. 1
Prophylactic Dosing
Low-Risk Patients
- Dosage: 5000 U subcutaneously every 8-12 hours 1
- Duration: Continue for 7 days or until patient is fully ambulatory, whichever is longer 2
- Administration: Use deep subcutaneous injection with a fine (25-26 gauge) needle to minimize tissue trauma 2
High-Risk Patients (e.g., total hip replacement)
- Dosage: Subcutaneous heparin every 12 hours, adjusted to prolong aPTT by 4-5 seconds into upper normal range 3
- Monitoring: Regular platelet count monitoring is recommended for early detection of heparin-induced thrombocytopenia 1
Treatment Dosing
Venous Thromboembolism
- Initial dose: 5000 U IV bolus 1
- Maintenance: 32,000 U per 24 hours by continuous IV infusion 1
- Alternative: 35,000-40,000 U per 24 hours subcutaneously 1
- Target: Adjust dose to maintain aPTT at 1.5-2.5 times control value 1, 3
- Duration: 5-day course is as effective as 10-day course 1
Coronary Heart Disease
Unstable angina or acute MI without thrombolytic therapy:
- Initial: 5000 U IV bolus
- Maintenance: 32,000 U per 24 hours by IV infusion
- Target: Maintain aPTT in therapeutic range 1
Acute MI after thrombolytic therapy:
- Initial: 5000 U IV bolus
- Maintenance: 24,000 U per 24 hours
- Target: Maintain aPTT in therapeutic range 1
Endovascular Procedures
- Pre-procedure: Consider aspirin with ticlopidine or clopidogrel for 3 days before procedure 4
- During procedure: Initial IV bolus of 100 units/kg followed by supplemental doses to maintain ACT between 300-350 seconds 4
- Post-procedure: For patients with complications (dissections, mural thrombosis, or new neurological symptoms), continue heparin to maintain aPTT at 1.5-2.3 times control values for 24 hours 1
Pediatric Dosing
- Initial dose: 75-100 units/kg IV bolus over 10 minutes 2
- Maintenance:
- Infants: 25-30 units/kg/hour (infants <2 months have highest requirements, averaging 28 units/kg/hour)
- Children >1 year: 18-20 units/kg/hour
- Older children: May require less heparin, similar to weight-adjusted adult dosage 2
- Target: Adjust to maintain aPTT of 60-85 seconds 2
Monitoring
- Initial testing: Baseline coagulation status (aPTT, INR, platelet count) 2
- Continuous IV infusion: Check aPTT approximately every 4 hours initially, then at appropriate intervals 2
- Intermittent IV injection: Perform coagulation tests before each injection during initiation 2
- Subcutaneous administration: Test 4-6 hours after injection 2
- Ongoing monitoring: Periodically monitor platelet counts, hematocrit, and occult blood in stool throughout therapy 2
Alternative Options
- Low molecular weight heparin (LMWH): Enoxaparin 1 mg/kg subcutaneously twice daily or 1.5 mg/kg once daily has shown equivalent efficacy to unfractionated heparin for venous thromboembolism 5
Special Considerations
- Heparin-induced thrombocytopenia (HIT): For patients with risk >1%, monitor platelet count every 2-3 days from day 4 to day 14 1
- Cardiovascular surgery: Initial dose of at least 150 units/kg; often 300 units/kg for procedures <60 minutes or 400 units/kg for procedures >60 minutes 2
- Converting to warfarin: Continue full heparin therapy until INR reaches stable therapeutic range 2
Pitfalls and Caveats
- Intramural thrombosis can occur in >90% of deeply injured arteries even with ACT elevated to 4-5 times control 1
- Avoid using heparin as a "catheter lock flush" product to prevent fatal medication errors 2
- Use different injection sites for subcutaneous administration to prevent hematoma development 2
- Use preservative-free heparin in neonates and infants 2
- Regular monitoring is essential as heparin has marked intra- and inter-patient variability in anticoagulant response 6