What are the guidelines for heparin (unfractionated heparin) loading and maintenance doses, and what is the typical duration of therapy?

Heparin Loading and Maintenance Dosing Guidelines

For adult patients requiring therapeutic anticoagulation, unfractionated heparin (UFH) should be administered with an initial bolus of 60-80 U/kg (maximum 4000 U) followed by a maintenance infusion of 12-18 U/kg/hour (maximum 1000 U/hour), adjusted to maintain an aPTT of 1.5-2.0 times control (approximately 50-70 seconds). 1, 2, 3

Adult Dosing Regimen

Initial Dosing

• Loading dose: 60-80 U/kg IV bolus (maximum 4000 U)
• Initial maintenance infusion: 12-18 U/kg/hour (maximum 1000 U/hour)

Monitoring and Dose Adjustment

• Check baseline coagulation parameters (aPTT, INR, platelet count) before starting therapy
• Measure aPTT 4-6 hours after initiation and 4-6 hours after any dose change
• Target aPTT: 1.5-2.0 times control (approximately 50-70 seconds)
• Once stable, monitor aPTT daily

Dose Adjustment Protocol

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

1

Duration of Therapy

The duration of UFH therapy depends on the clinical indication:

1. Venous thromboembolism (DVT/PE):

   • Minimum 5-7 days of therapeutic anticoagulation
   • Overlap with oral anticoagulant (warfarin) for at least 4-5 days
   • Continue UFH until INR is therapeutic (2.0-3.0) for 2 consecutive days 1, 4

2. Acute coronary syndromes:

   • Without thrombolytic therapy: 48 hours to 8 days
   • With thrombolytic therapy: 24-48 hours 1

3. Atrial fibrillation with embolism risk:

   • Until therapeutic on oral anticoagulant (if transitioning) 1

Pediatric Dosing

For pediatric patients, age-specific dosing is recommended:

• Loading dose: 75-100 U/kg IV bolus over 10 minutes
• Maintenance dose:
  • Infants < 1 year: 28 U/kg/hour
  • Children > 1 year: 20 U/kg/hour
• Target aPTT: 60-85 seconds (reflecting anti-Factor Xa level of 0.35-0.70) 1, 3

Special Considerations

Monitoring Parameters

• aPTT: Primary monitoring parameter; target 1.5-2.0 times control
• Platelet count: Monitor daily to detect heparin-induced thrombocytopenia (HIT)
• Hematocrit and occult blood in stool: Monitor periodically throughout therapy 1, 3

Alternative Monitoring

• Anti-Xa levels: Consider for patients with heparin resistance, inflammatory conditions, or those requiring unusually high doses (≥35,000 units/day)
• Target anti-Xa level: 0.3-0.7 IU/mL 2

Transitioning to Oral Anticoagulants

• To warfarin: Continue full-dose heparin until INR is in therapeutic range (2.0-3.0) for 2 consecutive days
• To other oral anticoagulants: Stop heparin infusion immediately after administering first dose of oral agent 3

Common Pitfalls and Caveats

1. Weight-based dosing is critical: Fixed dosing regimens often lead to subtherapeutic or supratherapeutic levels, increasing risk of treatment failure or bleeding 1, 5

2. Early monitoring is essential: Failure to achieve therapeutic aPTT within the first 24 hours is associated with increased risk of recurrent thromboembolism (up to 25%) 4, 6

3. Avoid intramuscular injections: These can cause hematoma; use intravenous or deep subcutaneous routes instead 3

4. Medication errors: Accidental overdose can occur when high-concentration vials (5,000 units/mL) are confused with low-concentration vials (50 units/mL) 1

5. Warfarin effect on aPTT: Concurrent warfarin therapy can artificially increase aPTT, potentially leading to inappropriate heparin dose reductions 7

By following these evidence-based guidelines for heparin loading, maintenance dosing, and monitoring, clinicians can optimize anticoagulation efficacy while minimizing bleeding complications, ultimately improving patient outcomes.