LMWHs as a class are about one-third the
molecular weight of the parent unfactionated heparin (UH) molecule.
The different LMWHs are produced by enzymatic or electro-chemical treatment
of the parent molecule. Their smaller molecular size eliminates many
of the extraneous interactions that UH has with plasma proteins and
cells. The result is a molecule that tends to interact only with antithrombin.
LMWHs have higher bioavailability and longer plasma half-lives than
UH. The drugs are given subcutaneously once or twice a day without the
need for anticoagulant monitoring in most patients. (exceptions include
significant renal failure, extremes of body weight and possibly pregnancy)
