Differentiation of the low-molecular-weight heparins.

The three low-molecular-weight heparins (LMWHs) available in the United States have been extensively evaluated for a wide array of indications. Properties associated with one LMWH cannot be assumed to be the same as those associated with another LMWH, as they are different pharmacologic entities. Therefore, therapeutic interchange of these agents is inappropriate. The pharmacokinetic and pharmacodynamic differences among LMWHs can be explained by comparing methods of preparation, molecular structures, half-lives, antithrombin- and non-antithrombin-mediated actions, effect on thrombus, and dosing interval. The Food and Drug Administration-approved indications and their respective levels of clinical evidence further differentiate these agents. A dichotomy in the results of clinical trials has been observed with the LMWHs. As the LMWHs are distinct compounds that each possess unique pharmacokinetic and pharmacodynamic profiles, treatment decisions should be based on the available safety and efficacy data for each LMWH. Agents should be prescribed only for those indications for which they have been shown to be effective and only at dosages that have been studied.