Studies comparing low molecular weight heparin with heparin for the treatment of thromboembolism: a literature review.

The use of heparin for the prophylaxis and treatment of venous and arterial thrombosis had been the standard of care for clinicians until 1982. At that time the introduction of depolymerized heparin for the prophylaxis of deep vein thrombosis in surgical patients was introduced. A number of such products, low molecular weight heparins (LMWH) were patented and introduced as new drugs during the ensuing of 20 years. Each LMWH had to be given a clinical trial against standard heparin for the several thromboembolic disorders for which heparin was the standard of care. By definition LMWH had to have unequal factor Xa and IIa inhibitor potency, expressed as a Xa-IIa ratio of greater than 1. They also had a molecular weight reduction to about one third that of heparin. A major advantage of LMWH over heparin was the subcutaneous route of injection for treatment of thrombotic disorders in contrast to the intravenous route for heparin. They had greater bioavailability than heparin by the subcutaneous route, a longer half-life and better predictability of dose response. It was found that routine laboratory monitoring was unnecessary. When given a trial against heparin, LMWH was equally safe and effective for most venous and arterial disorders. A new synthetic version of (pentasaccharide) both heparin and LMWH has been at least if not more effective than one LMWH (enoxaparin).