Heparin Dosing Recommendations for Anticoagulation
For patients requiring anticoagulation, unfractionated heparin should be administered using weight-based dosing with an initial IV bolus of 80 units/kg followed by an infusion of 18 units/kg/hour, with dose adjustments based on aPTT monitoring to maintain a therapeutic range of 1.5-2.5 times control. 1
Dosing Regimens by Clinical Indication
Venous Thromboembolism (VTE)
- Initial IV therapy:
- Subcutaneous administration options:
Acute Coronary Syndromes
- Unstable angina/NSTEMI:
- 60-70 units/kg bolus (maximum 5,000 units) followed by 12-15 units/kg/hour infusion (maximum 1,000 units/hour) 1
- STEMI with fibrinolytic therapy:
- 60 units/kg bolus (maximum 4,000 units) followed by 12 units/kg/hour infusion (maximum 1,000 units/hour) 1
Mechanical Heart Valves
- Mechanical mitral valves:
Monitoring and Dose Adjustment Protocol
Proper monitoring is essential to maintain therapeutic anticoagulation while minimizing bleeding risk. The following protocol should be used to adjust heparin dosing based on aPTT results 1, 2:
| aPTT (seconds) | aPTT (× control) | Action |
|---|---|---|
| <35 | <1.2 | 80 units/kg bolus; increase infusion rate by 4 units/kg/hour |
| 35-45 | 1.2-1.5 | 40 units/kg bolus; increase infusion rate by 2 units/kg/hour |
| 46-70 | 1.5-2.3 | No change (therapeutic range) |
| 71-90 | 2.3-3.0 | Reduce infusion rate by 2 units/kg/hour |
| >90 | >3.0 | Stop infusion for 1 hour, then reduce rate by 3 units/kg/hour |
- Check aPTT 6 hours after starting infusion and 6 hours after any dose change 2
- Once stable, check aPTT daily 1
Special Populations and Considerations
Renal Impairment
- In severe renal impairment, unfractionated heparin is preferred over LMWH due to risk of LMWH accumulation 1
- More frequent monitoring may be required
Obesity
- Weight-based dosing is particularly important in obese patients to ensure adequate anticoagulation 1
- Consider anti-Xa monitoring in morbidly obese patients 1
Pediatric Patients
- Initial dose: 75-100 units/kg IV bolus over 10 minutes
- Maintenance dose:
- Infants: 25-30 units/kg/hour (infants <2 months have highest requirements)
- Children >1 year: 18-20 units/kg/hour 3
Duration of Therapy
- For VTE, heparin should be continued for at least 5 days 1
- When transitioning to warfarin, continue heparin until INR is therapeutic (2.0-3.0) for at least 24 hours 1
- For mechanical heart valves, continue until INR reaches 2.5-3.5 2
Potential Complications and Management
Bleeding: Major bleeding occurs in approximately 1.9% of patients on therapeutic heparin 2
- Risk factors: High heparin dose, concomitant use of fibrinolytic agents or antiplatelet drugs, recent surgery/trauma, renal insufficiency, age >60 years 1
Heparin-induced thrombocytopenia (HIT):
- Monitor platelet count regularly during therapy 1
- If suspected, discontinue heparin and consult hematology
Clinical Pearls
- Weight-based dosing protocols have been shown to achieve therapeutic anticoagulation more rapidly and reduce recurrent thromboembolism compared to fixed-dose regimens 1
- Continuous IV infusion is associated with more stable anticoagulation and potentially lower bleeding risk compared to intermittent bolus dosing 1
- The therapeutic range of aPTT (1.5-2.5 times control) corresponds to a heparin level of 0.2-0.4 U/mL by protamine titration or an anti-factor Xa level of 0.3-0.7 U/mL 1
By following these evidence-based dosing recommendations and monitoring protocols, clinicians can optimize the efficacy and safety of unfractionated heparin therapy for patients requiring anticoagulation.