When injected subcutaneously, the bioavailability of UF ranges from 10-90%, whereas the bioavailability of LMW heparin is greater than 90% and is independent of dose. LMW heparins exhibit much less binding to plasma proteins than UF heparin, and do not accumulate in the liver or spleen, giving them a longer plasma half-life. The dose-response curve of LMW heparin also tends to be linear.
The therapeutic range for UF heparin is 0.3-0.7 IU/ml, while the range for LMW heparin is less clearly defined. Some clinicians maintain that is 0.4-1.1 IU/ml, or more conservatively, 0.5-1.0 IU/ml (anti-FXa method).