Unfractionated Heparin Dosing for a 50kg Patient
For a 50kg patient, the appropriate unfractionated heparin dosing is 60 U/kg (3000 U) IV bolus followed by an initial infusion of 12 U/kg/hour (600 U/hour) when treating venous thromboembolism, with dose adjustments based on aPTT monitoring targeting 1.5-2.0 times control (50-70 seconds). 1
Dosing Recommendations Based on Clinical Scenario
For Venous Thromboembolism (VTE) Treatment
- Initial bolus: 60 U/kg = 3000 U IV 1
- Initial infusion: 12 U/kg/hour = 600 U/hour 1
- Target aPTT: 1.5-2.0 times control (50-70 seconds) 1
- Monitor aPTT at 6 hours after initiation and adjust according to protocol 2
For Acute Coronary Syndrome (ACS)
- With primary PCI: 50-60 U/kg (2500-3000 U) IV bolus when used with GP IIb/IIIa inhibitors; 70-100 U/kg (3500-5000 U) when no GP IIb/IIIa inhibitor is planned 1
- With fibrinolytic therapy: 60 U/kg (3000 U) IV bolus with maximum of 4000 U, followed by infusion of 12 U/kg/hour with maximum of 1000 U/hour 1
- Without reperfusion therapy: Same dose as with fibrinolytic therapy 1
For Prophylaxis of Postoperative Thromboembolism
- 5000 U subcutaneously 2 hours before surgery and every 8-12 hours thereafter 3
Monitoring and Dose Adjustment
The following aPTT-based dose adjustment protocol should be used 2:
| aPTT (seconds) | Bolus (U/kg) | Hold (min) | Rate Change | Repeat aPTT |
|---|---|---|---|---|
| < 50 | 50 | 0 | ↑ 10% | 4 hours |
| 50-59 | 0 | 0 | ↑ 10% | 4 hours |
| 60-85 (target) | 0 | 0 | No change | Next day |
| 86-95 | 0 | 0 | ↓ 10% | 4 hours |
| 96-120 | 0 | 30 | ↓ 10% | 4 hours |
| > 120 | 0 | 60 | ↓ 15% | 4 hours |
Special Considerations for Low Body Weight
For patients with low body weight (50kg), several important considerations apply:
- Do not exceed the maximum initial bolus of 4000 U and maximum initial infusion rate of 1000 U/hour regardless of weight-based calculations 1
- Monitor more frequently for bleeding complications, as lower body weight can be a risk factor for bleeding 1
- Consider checking platelet counts daily to monitor for heparin-induced thrombocytopenia 2
- For patients with renal impairment, more careful monitoring is required due to increased risk of bleeding 2
Duration of Therapy
- For VTE: Minimum of 5-7 days of therapeutic anticoagulation, overlapping with oral anticoagulant (if transitioning) 2
- For ACS: 48 hours to 8 days without thrombolytic therapy; 24-48 hours with thrombolytic therapy 2
Potential Pitfalls and Caveats
- Underdosing risk: Patients may experience delayed time to therapeutic anticoagulation if initial dosing is inadequate 4
- Monitoring frequency: The first aPTT should be checked 6 hours after initiation of therapy to ensure appropriate dosing 2
- Bleeding risk: The risk of heparin-associated bleeding increases with higher doses and supratherapeutic clotting times 1
- Concomitant medications: Assess for medications that may interact with heparin, such as antiplatelet agents and other anticoagulants 2
- Transitioning to oral anticoagulants: When converting to warfarin, continue full heparin therapy until INR has reached a stable therapeutic range 3
By following these weight-based dosing recommendations and monitoring protocols, you can ensure safe and effective anticoagulation for your 50kg patient requiring unfractionated heparin therapy.