What is the standard dosing regimen for Unfractionated Heparin (UFH)?

Unfractionated Heparin Dosing

For therapeutic anticoagulation, administer UFH as an 80 units/kg IV bolus (maximum 4000 units) followed by 18 units/kg/hour continuous infusion (maximum 1000 units/hour), targeting an aPTT of 1.5-2.0 times control (approximately 50-70 seconds). 1, 2

Standard Weight-Based Dosing Regimen

Initial Dosing

• Bolus dose: 80 units/kg IV (maximum 4000 units for patients >50 kg) 1
• Infusion rate: 18 units/kg/hour (maximum 1000 units/hour for patients >55 kg) 1, 2
• This represents the highest quality evidence from the American College of Chest Physicians and FDA labeling 3, 2

Alternative Fixed-Dose Approach

• Bolus: 5,000 units IV 2
• Infusion: 1,000 units/hour continuous 2
• The American College of Chest Physicians suggests this fixed-dose approach is equivalent to weight-based dosing, though weight-based dosing is preferred 3

Context-Specific Modifications

STEMI with Fibrinolytic Therapy

Use reduced dosing to minimize bleeding risk: 3

• Bolus: 60 units/kg IV (maximum 4000 units) 3
• Infusion: 12 units/kg/hour (maximum 1000 units/hour) 3
• This lower dose is specifically recommended by ACC/AHA when combining UFH with fibrin-specific agents (alteplase, reteplase, tenecteplase) 3

Unstable Angina/NSTEMI

• Bolus: 60-70 units/kg IV 3
• Infusion: 12-15 units/kg/hour 3
• If glycoprotein IIb/IIIa inhibitors are planned during PCI, target ACT of 200 seconds rather than standard aPTT monitoring 3

Cardiovascular Surgery

• Minimum dose: 150 units/kg IV bolus 2
• For procedures <60 minutes: 300 units/kg 2
• For procedures >60 minutes: 400 units/kg 2

VTE Prophylaxis (Subcutaneous)

• 5,000 units subcutaneously 2 hours before surgery, then every 8-12 hours for 7 days or until fully ambulatory 2

Monitoring Protocol

aPTT Monitoring Schedule

• First check: 6 hours after bolus dose 2
• Subsequent checks: Every 4-6 hours until therapeutic, then daily once stable 2
• Target aPTT: 1.5-2.0 times control (approximately 50-70 seconds) 3, 1, 2

Additional Monitoring Requirements

• Platelet counts: Daily throughout therapy to detect heparin-induced thrombocytopenia 3, 2
• Hematocrit: Periodically 2
• Occult blood in stool: Periodically 2

Critical Dosing Pitfalls to Avoid

Excess Dosing Errors

Do not exceed maximum doses, as this significantly increases bleeding risk: 1, 4

• Maximum bolus: 70-80 units/kg or 4000 units total 1
• Maximum infusion: 18 units/kg/hour or 1000 units/hour total 1
• Research demonstrates that excess weight-adjusted dosing (>70 U/kg bolus or >15 U/kg/hour infusion) is associated with proportionally increased major bleeding 4

High-Risk Populations for Overdosing

Elderly patients and women are at highest risk for receiving excess weight-adjusted doses: 4

• Patients with lower body weight frequently receive fixed doses (e.g., 5,000 unit bolus, 1,000 units/hour infusion) that exceed weight-based recommendations 4
• Age (per 10-year increase) and female sex are strongly associated with excess dosing 4

Morbidly Obese Patients

Use adjusted body weight formulas rather than actual body weight in morbidly obese patients (BMI ≥40): 5, 6

• Standard weight-based protocols with maximum dose caps can cause significant delays in achieving therapeutic anticoagulation 5
• Consider: Dosing weight = IBW + 0.3(ABW - IBW) or IBW + 0.4(ABW - IBW) 5
• Morbidly obese patients require smaller infusion rates per kilogram actual body weight (approximately 11.5 units/kg/hour vs 13.5 units/kg/hour in normal weight patients) 6

Special Populations

Pediatric Dosing

Use preservative-free formulations in neonates and infants: 2

• Initial bolus: 75-100 units/kg IV over 10 minutes 2
• Infusion for infants: 25-30 units/kg/hour (infants <2 months require highest doses, averaging 28 units/kg/hour) 2
• Infusion for children >1 year: 18-20 units/kg/hour 2
• Target aPTT: 60-85 seconds (reflecting anti-Factor Xa level of 0.35-0.70) 2

Chronic Kidney Disease

UFH is the preferred anticoagulant in severe renal insufficiency (CrCl <30 mL/min): 7

• Use standard weight-based dosing without dose reduction 7
• UFH undergoes hepatic metabolism rather than renal excretion, making it safer than LMWH in advanced CKD 7
• LMWH is contraindicated when CrCl <30 mL/min due to drug accumulation 7

Absolute Contraindications

Do not administer UFH in the following situations: 2

• Active or history of heparin-induced thrombocytopenia (HIT) 7, 2
• Known hypersensitivity to heparin or pork products 2
• Uncontrolled active bleeding (except in disseminated intravascular coagulation) 2
• Recent neuraxial anesthesia (risk of spinal hematoma) 7

Duration of Therapy

With Fibrinolytic Therapy

• Minimum duration: 48 hours 3
• Preferred duration: Up to 8 days or duration of hospitalization 3
• Prolonged UFH infusions beyond 48 hours increase risk of heparin-induced thrombocytopenia without clear benefit unless ongoing indication exists 3

Transition to Oral Anticoagulation

For warfarin: Continue full-dose UFH for several days until INR reaches stable therapeutic range, then discontinue without tapering 2

For direct oral anticoagulants: Stop IV UFH immediately after first dose of oral anticoagulant, or start oral agent 0-2 hours before next scheduled intermittent UFH dose 2