Half-Life of Unfractionated Heparin

Pharmacokinetic Characteristics

The American Thoracic Society notes that the half-life of unfractionated heparin is dose-dependent and nonlinear, ranging from approximately 30 minutes after a low-dose IV bolus to 60 minutes with a standard bolus, and up to 150 minutes with high-dose administration 1, 2
At a dose of 25 units/kg IV bolus, the half-life is approximately 30 minutes 1, 2
At a dose of 100 units/kg IV bolus, the half-life extends to approximately 60 minutes 1, 2, 3
At a dose of 400 units/kg IV bolus, the half-life can reach 150 minutes 1, 2

The half-life of unfractionated heparin is influenced by a rapid saturable mechanism and a slower first-order mechanism, with the rapid mechanism predominating at therapeutic doses 1, 2
The dual clearance pathway renders the anticoagulant response nonlinear at therapeutic doses, with both intensity and duration of effect rising disproportionately with increasing dose 1, 2

The American College of Chest Physicians recommends monitoring activated partial thromboplastin time (aPTT) during therapeutic anticoagulation due to the variable half-life of unfractionated heparin 1, 2
The effective biological half-life increases nonlinearly with dose, meaning doubling the heparin dose more than doubles the duration of anticoagulant effect 1, 2, 3