Unfractionated Heparin Dosing Recommendations for Anticoagulation
For patients requiring anticoagulation, weight-based dosing of unfractionated heparin is recommended with an initial IV bolus of 80 units/kg followed by a continuous infusion of 18 units/kg/hour, adjusted to maintain aPTT at 1.5-2.5 times control value. 1
Dosing Regimens by Indication
Venous Thromboembolism (VTE)
- Initial dosing options:
- Subcutaneous administration options (if IV not feasible):
Acute Coronary Syndromes
- Unstable angina/NSTEMI:
- 60-70 units/kg IV 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 IV bolus (maximum 4,000 units) followed by 12 units/kg/hour infusion (maximum 1,000 units/hour) 1
Mechanical Heart Valves
- 5,000 units IV bolus followed by 32,000 units/24 hours continuous infusion 2
Monitoring and Dose Adjustment
Target aPTT Range
- Maintain aPTT at 1.5-2.5 times control value 1
- This corresponds to a heparin level of 0.2-0.4 U/mL by protamine titration or anti-factor Xa level of 0.3-0.7 U/mL 1
Dose Adjustment Protocol
- aPTT <35 seconds (<1.2× control): 80 U/kg bolus; increase infusion rate by 4 U/kg/hour 1, 2
- aPTT 35-45 seconds (1.2-1.5× control): 40 U/kg bolus; increase infusion rate by 2 U/kg/hour 1, 2
- aPTT 46-70 seconds (1.5-2.3× control): No change (therapeutic range) 1, 2
- aPTT 71-90 seconds (2.3-3× control): Decrease infusion rate by 2 U/kg/hour 1, 2
- aPTT >90 seconds (>3× control): Stop infusion for 1 hour, then decrease rate by 3 U/kg/hour 1, 2
Monitoring Schedule
- Check baseline coagulation status (aPTT, INR, platelet count) 3
- First aPTT check 6 hours after starting infusion 2
- Continue monitoring approximately every 4-6 hours until stable, then at appropriate intervals 3
- For subcutaneous administration, check aPTT 4-6 hours after injection 1
- Monitor platelet count regularly to detect heparin-induced thrombocytopenia 1
Special Considerations
Pediatric Dosing
- Initial dose: 75-100 units/kg IV bolus over 10 minutes 3
- Maintenance dose:
- Infants: 25-30 units/kg/hour (infants <2 months have highest requirements)
- Children >1 year: 18-20 units/kg/hour 3
Renal Impairment
- Consider unfractionated heparin over LMWH in severe renal impairment 1
- Monitor more frequently for accumulation and bleeding risk 1
Obesity
- Weight-based dosing is particularly important in obese patients to ensure adequate anticoagulation 1
Duration of Therapy
- For VTE: Minimum 5 days, overlapping with oral anticoagulants 1
- Continue heparin until INR is therapeutic (2.0-3.0) for at least 24 hours if transitioning to warfarin 1
Potential Complications and Pitfalls
Bleeding Risk
- Risk increases with higher doses, concomitant use of fibrinolytics or antiplatelet agents, recent surgery, trauma, or invasive procedures 1
- Higher risk in patients >60 years, with hepatic dysfunction, or multiple comorbidities 1
Heparin Resistance
- May occur in inflammatory states with elevated acute phase reactants, especially fibrinogen 1
- Consider anti-Xa monitoring rather than aPTT in these cases 1
Heparin-Induced Thrombocytopenia (HIT)
- Monitor platelet count regularly throughout therapy 1
- If HIT is suspected, discontinue heparin immediately and switch to a non-heparin anticoagulant 1
Weight-based dosing protocols have been shown to achieve therapeutic anticoagulation more rapidly and with fewer complications than fixed-dose regimens, leading to lower rates of recurrent thromboembolism 1. The appropriate dosing strategy should be selected based on the specific indication, patient characteristics, and clinical setting.