What is the appropriate heparin (unfractionated heparin) dosing regimen for a typical adult patient with deep vein thrombosis or pulmonary embolism and no significant impaired renal function?

Unfractionated Heparin Dosing for DVT/PE in Adults with Normal Renal Function

For treatment of deep vein thrombosis or pulmonary embolism in adults without renal impairment, administer unfractionated heparin as an initial IV bolus of 80 units/kg (or 5,000 units) followed by continuous IV infusion of 18 units/kg/hour (or 32,000-40,000 units per 24 hours), adjusted to maintain aPTT at 1.5-2.5 times control. 1, 2

Initial Dosing Regimen

The weight-based dosing approach is superior to fixed-dose regimens:

• IV bolus: 80 units/kg (maximum 5,000-10,000 units) 1, 2
• Continuous IV infusion: 18 units/kg/hour 1, 2
• Alternative fixed-dose regimen: 5,000 units IV bolus followed by 32,000-40,000 units per 24 hours by continuous infusion 1

Weight-based dosing achieves therapeutic anticoagulation more rapidly and reduces recurrent thromboembolism compared to fixed dosing. 1 Patients who fail to achieve therapeutic aPTT within 24 hours have significantly higher recurrence rates (up to 25%) compared to those achieving therapeutic levels early (2% recurrence). 3

Monitoring and Dose Adjustment

• Target aPTT: 1.5-2.5 times control (equivalent to heparin level 0.2-0.4 U/mL or anti-Factor Xa 0.30-0.7 U/mL) 1
• Initial monitoring: Check aPTT 6 hours after starting infusion and 6 hours after any dose adjustment 2
• Ongoing monitoring: Once therapeutic, check aPTT daily 2
• Additional monitoring: Periodically monitor platelet counts, hematocrit, and occult blood in stool throughout therapy 2

The compressed therapeutic range (1.5-2.5 rather than the older 1.5-2.5+ range) requires closer monitoring to maintain adequate anticoagulation without excessive bleeding risk. 4

Duration and Transition to Oral Anticoagulation

• Heparin duration: Continue for minimum 5-7 days 1, 2, 5
• Warfarin overlap: Start warfarin within 24 hours of initiating heparin and continue both agents for at least 5 days AND until INR is therapeutic (2.0-3.0) for 24 consecutive hours 2, 6
• Total anticoagulation: Minimum 3 months for most patients 1, 7

Alternative Route: Subcutaneous Administration

If IV access is problematic, subcutaneous heparin is an acceptable alternative:

• Initial dose: 5,000 units IV bolus, then 250 units/kg subcutaneously every 12 hours 1
• Alternative: 333 units/kg subcutaneously initially, then 250 units/kg every 12 hours 1
• Monitoring: Check aPTT 4-6 hours after injection 2

Critical Pitfalls to Avoid

Subtherapeutic dosing in first 24 hours: This is the most common and dangerous error. Failure to achieve aPTT >1.5 times control within 24 hours increases recurrent VTE risk from 2% to 25%. 3 Use weight-based dosing and check aPTT at 6 hours to ensure therapeutic levels are achieved rapidly. 1, 2

Premature discontinuation: Heparin must overlap with warfarin for at least 5 days AND until INR is therapeutic for 24 hours. 2 Starting warfarin alone without heparin coverage leaves patients vulnerable to recurrent thrombosis during the initial prothrombotic phase of warfarin therapy. 5

Inadequate monitoring: The narrower therapeutic window (1.5-2.5 times control) requires vigilant monitoring. 4 Both subtherapeutic and supratherapeutic levels are common without proper dose adjustment. 1

When to Choose Unfractionated Heparin Over LMWH

While LMWH is generally preferred for DVT treatment due to superior mortality and bleeding outcomes 1, unfractionated heparin remains the appropriate choice in specific situations:

• Severe renal insufficiency (creatinine clearance <30 mL/min) 1, 7
• Hemodynamic instability or high-risk PE requiring potential thrombolysis 7
• High bleeding risk requiring rapid reversibility with protamine 7
• Morbid obesity where LMWH dosing is uncertain 7

For pulmonary embolism specifically, both unfractionated heparin and LMWH are considered equally appropriate initial treatments. 1