Starting Dose of Unfractionated Heparin for a 50 kg Patient
For a 50 kg patient, the appropriate starting dose of unfractionated heparin (UFH) is a bolus of 3,000 units followed by an initial infusion of 600 units/hour. 1, 2
Weight-Based Dosing Calculation
The recommended weight-based dosing for therapeutic anticoagulation with UFH follows this algorithm:
Initial bolus dose: 60 U/kg (maximum 4,000 U)
- For a 50 kg patient: 60 U/kg × 50 kg = 3,000 U
Initial infusion rate: 12 U/kg/hour (maximum 1,000 U/hour)
- For a 50 kg patient: 12 U/kg/hour × 50 kg = 600 U/hour
Monitoring and Adjustment
After initiating therapy, the UFH infusion should be adjusted based on activated partial thromboplastin time (aPTT) monitoring:
- Check baseline aPTT, INR, and platelet count before starting therapy
- Monitor aPTT approximately every 4-6 hours during initial treatment
- Target aPTT: 1.5-2.0 times the control value (approximately 50-70 seconds) 1, 2
Adjustment Protocol Based on aPTT Results
| aPTT (seconds) | aPTT (× control) | Action |
|---|---|---|
| <35 | <1.2 | 80 U/kg bolus; increase infusion by 4 U/kg/hour |
| 35-45 | 1.2-1.5 | 40 U/kg bolus; increase infusion by 2 U/kg/hour |
| 46-70 | 1.5-2.3 | No change (therapeutic range) |
| 71-90 | 2.3-3.0 | Reduce infusion by 2 U/kg/hour |
| >90 | >3.0 | Stop infusion for 1 hour, then reduce by 3 U/kg/hour |
Important Considerations
Avoid excessive dosing: The ACC/AHA guidelines define excessive initial UFH dosing as an initial bolus >70 U/kg, a total initial bolus >4,000 U, or an initial infusion >15 U/kg/hour or >1,000 U/hour 1
Monitor for complications: Regularly monitor platelet counts, hematocrit, and check for occult blood in stool throughout therapy 1, 2
Renal function: UFH is the preferred anticoagulant for patients with severe renal dysfunction (CrCl <30 mL/min) as it's primarily metabolized by the liver 3
Duration of therapy: There is no benefit to prolonging UFH infusion beyond 48 hours in the absence of ongoing indications for anticoagulation, and prolonged infusions increase the risk of heparin-induced thrombocytopenia 1
Special Considerations for Lower Weight Patients
While most UFH dosing studies focus on average or higher-weight patients, it's important to note that lower-weight patients like this 50 kg individual may be more sensitive to standard dosing. The maximum caps (4,000 U bolus and 1,000 U/hour infusion) are designed for patients weighing >70 kg, so this patient would receive proportionally lower doses based on their weight 1, 2.
By following this weight-based dosing approach, you can minimize the risk of both inadequate anticoagulation and excessive bleeding in this 50 kg patient.