LMW heparin is preferred over unfractionated heparin because:
LMW heparin inhibit factor Xa only and have a weak effect on thrombin , aPTT, or CT are not prolonged. Heparin acts by activation of antithrombin III. LMW heparin is given subcutaneosly due to better bioavalability.LMW heparin have subcutaneous bioavalability of 70 - 90%. From medical pharmacology padmaja 4th edition Page no 337
Hematology
LMW heparin directly inhibit thrombin whereas unfractionated heparin acts activation of anti thrombin
LMW heparins have higher risk of causing bleeding
LMW heparin can be given subcutaneously as well as orally
LMW heparin has consistent bioavailability.
LMW heparin has consistent bioavailability.