Low molecular weight heparin

Low-molecular-weight heparin (LMWH) is a class of anticoagulant medications. They are used in the prevention of blood clots and treatment of venous thromboembolism (deep vein thrombosis and pulmonary embolism) and in the treatment of myocardial infarction. Low-molecular-weight heparin (LMWH) is a class of anticoagulant medications. They are used in the prevention of blood clots and treatment of venous thromboembolism (deep vein thrombosis and pulmonary embolism) and in the treatment of myocardial infarction. Heparin is a naturally occurring polysaccharide that inhibits coagulation, the process that leads to thrombosis. Natural heparin consists of molecular chains of varying lengths, or molecular weights. Chains of varying molecular weights, from 5000 to over 40,000 Daltons, make up polydisperse pharmaceutical-grade heparin. LMWHs, in contrast, consist of only short chains of polysaccharide. LMWHs are defined as heparin salts having an average molecular weight of less than 8000 Da and for which at least 60% of all chains have a molecular weight less than 8000 Da. These are obtained by various methods of fractionation or depolymerisation of polymeric heparin. Heparin derived from natural sources, mainly porcine intestine or bovine lung, can be administered therapeutically to prevent thrombosis. However, the effects of natural, or unfractionated heparin are more unpredictable than LMWH. Because it can be given subcutaneously and does not require APTT monitoring, LMWH permits outpatient treatment of conditions such as deep vein thrombosis or pulmonary embolism that previously mandated inpatient hospitalization for unfractionated heparin administration. Because LMWH has more predictable pharmacokinetics and anticoagulant effect, LMWH is recommended over unfractionated heparin for patients with massive pulmonary embolism, and for initial treatment of deep vein thrombosis. As compared to placebo or no intervention, prophylactic treatment of hospitalized medical patients using LMWH and similar anticoagulants reduces the risk of venous thromboembolism, notably pulmonary embolism. More recently these agents have been evaluated as anticoagulants in acute coronary syndrome (ACS) managed by percutaneous intervention (PCI). The use of LMWH needs to be monitored closely in patients at extremes of weight or in-patients with renal dysfunction. An anti-factor Xa activity may be useful for monitoring anticoagulation. Given its renal clearance, LMWH may not be feasible in patients that have end-stage renal disease. LMWH can also be used to maintain the patency of cannulae and shunts in dialysis patients. Patients with cancer are at higher risk of venous thromboembolism and LMWHs are used to reduce this risk. The CLOT study, published in 2003, showed that, in patients with malignancy and acute venous thromboembolism, dalteparin was more effective than warfarin in reducing the risk of recurrent embolic events. Use of LMWH in cancer patients for at least the first 3 to 6 months of long-term treatment is recommended in numerous guidelines and is now regarded as a standard of care. The use of LMWHs should be avoided in patients with known allergies to LMWHs, heparin, sulfites or benzyl alcohol, in patients with active major bleeding, or patients with a history of heparin-induced low blood platelet count (also known as heparin-induced thrombocytopenia or HIT). High treatment doses are contraindicated in acute bleedings such as cerebral or gastrointestinal haemorrhage.LMWHs are more dependent on renal function for their excretion than unfractionated heparin so their biological half-life may be prolonged in patients with renal failure and therefore their use in the setting of creatinine clearance rate (CrCl) <30 mL/min may need to be avoided. Apart from using unfractionated heparin instead, it may be possible to reduce the dose and/or monitor the anti-Xa activity to guide treatment.