What is the typical dose of heparin for a patient requiring anticoagulation therapy, considering factors such as weight, renal function, and specific clinical scenario?

Heparin Dosing for Anticoagulation Therapy

For therapeutic anticoagulation with unfractionated heparin (UFH), use weight-based dosing with an initial IV bolus of 80 units/kg followed by continuous infusion of 18 units/kg/hour, targeting an aPTT of 1.5-2.5 times baseline. 1

Initial Dosing Regimens

Intravenous UFH (Preferred for VTE Treatment)

Weight-based dosing is superior to fixed-dose regimens and significantly reduces recurrent thromboembolism. 1

• Standard therapeutic dose: 80 units/kg IV bolus, then 18 units/kg/hour continuous infusion 1, 2
• Alternative regimen: 5,000 units IV bolus followed by at least 32,000 units/24 hours (minimum 1,000 units/hour infusion) 1
• Target aPTT: 1.5-2.5 times baseline (corresponding to anti-Factor Xa levels of 0.3-0.7 IU/mL) 1, 2

Subcutaneous UFH (Alternative Route)

• Option 1: 5,000 units IV bolus, then 250 units/kg subcutaneously every 12 hours 1
• Option 2: 333 units/kg subcutaneous initial dose, then 250 units/kg every 12 hours 1, 2

Acute Coronary Syndromes (Lower Doses Required)

• NSTE-ACS: 60-70 units/kg IV bolus (maximum 5,000 units), then 12-15 units/kg/hour infusion (maximum 1,000 units/hour) 1
• During PCI: 70-100 units/kg IV bolus if not previously anticoagulated; 50-70 units/kg if receiving concomitant GP IIb/IIIa inhibitors 1

Monitoring and Dose Adjustment

Achieving therapeutic aPTT within 24 hours is critical—failure to do so increases recurrent VTE risk to 25% compared to 2% with adequate anticoagulation. 1

• Initial monitoring: Check aPTT at baseline, then approximately every 4 hours after starting infusion until stable 2
• Intermittent IV dosing: Check aPTT before each injection 2
• Subcutaneous dosing: Optimal sampling time is 4-6 hours after injection 2
• Ongoing monitoring: Monitor platelet counts, hematocrit, and occult blood in stool throughout therapy 2

Special Population Adjustments

Severe Renal Insufficiency (CrCl <30 mL/min)

For patients requiring LMWH with severe renal impairment, reduce the dose rather than using standard doses. 1

• UFH is preferred over LMWH as it does not require renal dose adjustment (primarily hepatic metabolism) 3
• Enoxaparin: If used, reduce to 1 mg/kg once daily (instead of twice daily) 1
• Monitor anti-Xa levels more frequently 1

Obesity (BMI ≥30 or Weight >100 kg)

• Use actual body weight for dosing calculations 1
• Class 3 obesity (BMI ≥40): Consider using ideal body weight (IBW) to avoid overdosing, particularly during procedures requiring ACT monitoring 1
• Monitor aPTT or ACT carefully as conventional nomograms may lead to supratherapeutic levels 1

Underweight Patients

• Use actual body weight for calculations 1
• Monitor more frequently for bleeding risk 1

Pediatric Dosing

Use preservative-free formulations in neonates and infants. 2

• Initial dose: 75-100 units/kg IV bolus over 10 minutes 2
• Maintenance infusion:
  • Infants: 25-30 units/kg/hour (infants <2 months require highest doses, averaging 28 units/kg/hour) 2
  • Children >1 year: 18-20 units/kg/hour 2
• Target aPTT: 60-85 seconds (corresponding to anti-Factor Xa 0.35-0.70) 2

Clinical Scenario-Specific Dosing

VTE Prophylaxis (Low-Dose)

• Medical patients: 5,000 units subcutaneously every 8-12 hours 1, 2
• Surgical prophylaxis: 5,000 units 2 hours preoperatively, then every 8-12 hours for ≥7-10 days 1, 2
• High-risk surgical patients: Consider extended prophylaxis up to 4 weeks 1

Cardiovascular Surgery

• Total body perfusion: Minimum 150 units/kg; typically 300 units/kg for procedures <60 minutes or 400 units/kg for procedures >60 minutes 2

CRRT Anticoagulation

• Standard protocol: Adjust dose to maintain aPTT 1.5-2.0 times baseline 3
• Alternative for HIT: Argatroban 0.5-1.2 μg/kg/min (no bolus) targeting aPTT 1.5-3 times baseline, or bivalirudin 0.15-0.20 mg/kg/hour (no bolus) targeting aPTT 1.5-2.5 times baseline 3

Extracorporeal Dialysis

• Initial dose: 25-30 units/kg bolus 2
• Maintenance infusion: 1,500-2,000 units/hour 2

Critical Pitfalls to Avoid

Fixed-dose regimens are inferior to weight-based dosing and result in higher recurrence rates. 1

• Never use fixed 5,000-unit bolus with 1,000 units/hour infusion—this underdoses most patients and increases VTE recurrence 1
• Do not delay achieving therapeutic aPTT—subtherapeutic anticoagulation in first 24 hours dramatically increases recurrence risk 1, 3
• Avoid intramuscular administration due to high risk of hematoma formation 2
• Do not confuse 1 mL treatment vials with catheter lock flush vials—this is a critical safety issue 2
• Monitor for heparin-induced thrombocytopenia (HIT): Check platelet counts every 2-3 days from day 4-14 in patients with ≥1% HIT risk 1

Transitioning to Oral Anticoagulation

Converting to Warfarin

• Overlap full-dose heparin with warfarin for several days until INR reaches stable therapeutic range (2-3) 2
• Do not taper heparin—discontinue abruptly once INR therapeutic 2
• Typical overlap duration: 4-5 days 1

Converting to DOACs

• Stop IV heparin immediately after administering first DOAC dose 2
• For intermittent IV heparin: Start DOAC 0-2 hours before next scheduled heparin dose 2