What is the typical dose of heparin (unfractionated heparin) for a patient requiring therapeutic anticoagulation, considering factors such as weight and impaired renal function?

Heparin Dosing for Therapeutic Anticoagulation

Standard Weight-Based Dosing

For therapeutic anticoagulation, administer unfractionated heparin as an 80 units/kg IV bolus (maximum 4000 units) followed by continuous infusion at 18 units/kg/hour, targeting an aPTT of 1.5-2.5 times baseline (corresponding to anti-Factor Xa levels of 0.3-0.7 IU/mL). 1, 2, 3

Initial Dosing Protocol

• Bolus dose: 80 units/kg IV (maximum 4000 units) 1, 2, 3
• Continuous infusion: 18 units/kg/hour 1, 2, 3
• Alternative regimen: 5000 units IV bolus followed by at least 32,000 units per 24 hours (minimum 1000 units/hour) 1, 2

Monitoring Requirements

• Check aPTT 6 hours after initiating therapy or any rate change 4, 3
• Continue checking aPTT every 6 hours until two consecutive therapeutic values are achieved 4
• Once stable, monitor aPTT every 24 hours 4
• Target aPTT: 1.5-2.5 times baseline (approximately 45-75 seconds), which correlates with anti-Factor Xa levels of 0.3-0.7 IU/mL 1, 2
• Monitor platelet counts every 2-3 days from day 4-14 to screen for heparin-induced thrombocytopenia 2, 3

Renal Impairment Considerations

Unfractionated heparin does NOT require dose adjustment in renal impairment because it undergoes hepatic metabolism, making it the preferred anticoagulant over low-molecular-weight heparins in patients with severe renal dysfunction. 2, 5

• Standard weight-based dosing (80 units/kg bolus, 18 units/kg/hour) applies regardless of creatinine clearance 2, 5
• Continue to titrate based on aPTT monitoring rather than empirically reducing doses 4, 5
• Low-molecular-weight heparins should be avoided when creatinine clearance is <30 mL/min due to accumulation risk 1, 5

Critical Pitfalls to Avoid

• Never use fixed-dose regimens when weight information is available—this increases recurrent thromboembolism risk 5-15 fold compared to weight-based dosing 4, 2
• Achieve therapeutic aPTT within 24 hours—delays are associated with 25% recurrence rate of venous thromboembolism versus 2% when therapeutic levels are reached promptly 4, 2, 6
• Do not confuse the 1 mL therapeutic vial with catheter lock flush vials 3
• Avoid intramuscular administration due to high risk of hematoma formation 3

Special Populations

Acute Coronary Syndrome Patients

• Use lower dosing: 60 units/kg bolus (maximum 4000 units) followed by 12 units/kg/hour infusion (maximum 1000 units/hour) 4
• This reduced regimen decreases bleeding risk when combined with fibrinolytics or GP IIb/IIIa inhibitors 1, 4

Obese Patients

• Use actual body weight for dosing calculations 2
• Monitor aPTT closely as standard nomograms remain valid 2

Patients Requiring CRRT

• Standard weight-based dosing applies (80 units/kg bolus, 18 units/kg/hour) 7
• Target aPTT 1.5-2.0 times baseline during continuous renal replacement therapy 7
• If heparin-induced thrombocytopenia develops, switch to argatroban at 0.5-1.2 μg/kg/min without bolus 7, 8

Subcutaneous Alternative Regimen

For patients unable to receive continuous IV infusion: 1, 3

• Initial dose: 5000 units IV bolus, followed by 10,000-20,000 units subcutaneously every 8 hours 1, 3
• Alternative: 15,000-20,000 units subcutaneously every 12 hours 1, 3
• Administer deep subcutaneously above the iliac crest or in abdominal fat layer using a 25-26 gauge needle 3
• Check aPTT 4-6 hours after injection for dose adequacy 3

Weight Change During Therapy

• If weight changes within the first 24 hours of therapy, recalculate the infusion rate using the corrected weight with the standard formula (18 units/kg/hour) 4
• Check aPTT 6 hours after any rate adjustment 4
• Continue to titrate primarily based on aPTT values rather than weight alone 4