Intravenous heparin has a shorter duration of effect than subcutaneous heparin, requiring more frequent dosing to maintain continuous anticoagulation. While intravenous heparin produces higher peak anticoagulation immediately after a dose, its effects wear off quicker, potentially leading to periods without therapeutic anticoagulation and increased clot risk. Subcutaneous heparin has a more sustained effect over 8-12 hours that reduces fluctuations in anticoagulation levels but results in lower peak levels and a reduced bleed risk. Due to differences in pharmacokinetics and anticoagulation profiles, intravenous and subcutaneous heparin are not interchangeable and must be administered as prescribed.