Pharmacokinetics of heparin and low molecular weight heparins

The main kinetic features of heparin and low molecular weight heparins (LMWHs) are reviewed. The complexities related to the study of a nonhomogeneous drug containing fractions with different molecular weight and pharmacological effects are discussed along with the possible bias due to the prevalent use of indirect measures of drug concentration. Available data show that LMWHs have longer half-lives with respect to that of heparin and higher bioavailabilities after subcutaneous administration; experimental and clinical evidences suggest that the kinetics of heparin and LMWHs can only be described taking into account the presence of an endogenous pool from which these drugs are released with different speeds and after various types of manipulations.