What is the recommended intravenous (IV) dose of heparin (unfractionated heparin) for therapeutic anticoagulation?

Recommended IV Heparin Dose for Therapeutic Anticoagulation

For therapeutic anticoagulation, administer an initial IV bolus of 80 units/kg followed by a continuous infusion of 18 units/kg/hour, with dose adjustments based on aPTT monitoring to maintain a target of 1.5-2.5 times control (typically 45-75 seconds). 1, 2, 3

Initial Dosing Regimen

Weight-based dosing is superior to fixed-dose regimens and should be used in all patients when weight is available 1, 2:

• Bolus: 80 units/kg IV push 4, 1, 3
• Infusion: 18 units/kg/hour continuous IV 4, 1, 3

If patient weight is unavailable, an alternative fixed-dose regimen consists of 5,000 units IV bolus followed by at least 32,000 units/24 hours continuous infusion 1. However, this approach is associated with higher rates of subtherapeutic anticoagulation 1, 2.

Monitoring and Dose Adjustments

The first aPTT should be checked 4-6 hours after the initial bolus, with subsequent monitoring after any dose change and daily once therapeutic range is achieved 1, 5. The target aPTT is 1.5-2.5 times control value, typically 45-75 seconds 1, 3.

aPTT-Based Dose Adjustment Protocol

Use the following standardized nomogram for dose adjustments 4, 1:

• aPTT <35 seconds (<1.2 times control): Give 80 units/kg bolus; increase infusion by 4 units/kg/hour 4
• aPTT 35-45 seconds (1.2-1.5 times control): Give 40 units/kg bolus; increase infusion by 2 units/kg/hour 4
• aPTT 46-70 seconds (1.5-2.3 times control): No change needed 4
• aPTT 71-90 seconds (2.3-3.0 times control): Reduce infusion by 2 units/kg/hour 4
• aPTT >90 seconds (>3.0 times control): Stop infusion for 1 hour, then reduce infusion by 3 units/kg/hour 4

Critical Timing Considerations

Achieving therapeutic aPTT within 24 hours is essential, as failure to do so is associated with a 25% risk of recurrent venous thromboembolism and significantly higher mortality in pulmonary embolism patients 1, 2, 3. Early therapeutic anticoagulation is the primary objective to prevent death and recurrent events 4.

Duration and Transition to Oral Anticoagulation

Continue heparin for at least 5 days with overlap of warfarin for at least 4-5 days 1. Discontinue heparin only when INR is ≥2.0 for at least 24 hours 1. Do not taper heparin when discontinuing 5.

Common Pitfalls to Avoid

• Using fixed-dose regimens instead of weight-based dosing leads to subtherapeutic anticoagulation and increased recurrence rates of up to 25% 1, 2
• Applying lower ACS dosing protocols (60 units/kg bolus, 12 units/kg/hour) to VTE patients results in inadequate anticoagulation and higher recurrence rates 2
• Failure to achieve therapeutic aPTT within 24 hours is associated with higher mortality in pulmonary embolism 1, 2, 3
• Inadequate monitoring frequency can lead to either subtherapeutic anticoagulation or excessive bleeding 1
• Discontinuing heparin before warfarin reaches therapeutic levels can lead to treatment failure 1

Special Populations

Pediatric patients require higher weight-based doses: infants (<1 year) need 28 units/kg/hour, children (1-15 years) need 20 units/kg/hour, and adolescents (≥15 years) need 18 units/kg/hour 1. The initial bolus for pediatric patients is 50 units/kg 5.

Geriatric patients over 60 years may require lower doses 5.