LOW-MOLECULAR-WEIGHT HEPARINS - VALUABLE NEW HEPARIN SUBSTITUTES

Low molecular weight (LMW) heparins are being substituted for heparin in many clinical disorders. Many clinical trials are completed or are in progress at this time. LMW heparin was first produced from standard heparin by chromatographic procedures. Chemical and/or enzymatic clea vage of the heparin molecules has made possible the production of seve ral LMW heparins, each of which has its own unique mix of glycosaminog lycans. Because the chemical composition and biologic activities of ea ch LMW heparin differ from the others, each one must be clinically val idated for a particular thrombotic disorder or prophylactic use. Some of the properties of LMW heparins that distinguish them from standard heparin include a high ratio of anti-Xa activity to antithrombin activ ity, a high bioavailability by the s.c. route, and a long half-life wh ether given i.v. or s.c. Monitoring of their blood levels by coagulati on tests and enzyme inhibitor assays is possible but is not usually ne cessary because the blood level achieved for a given dose is quite pre dictable. The half-life is unusually prolonged in patients with renal failure, which could be a disadvantage, that would require laboratory monitoring. Recent studies have shown LMW heparins to be efficacious f or prophylaxis of deep vein thrombosis (DVT) in surgical patients, for treatment of venous thromboembolism, and for extracorporeal circuits. Trials for arterial disorders are ongoing. It is quite probable that LMW heparins will someday replace heparin for all indications. This wi ll result in fewer cases cf heparin-induced thrombocytopenia and throm bosis, which at the present time is a significant cause of death and d isability in patients receiving heparin.