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Encyclopedia > Low molecular weight heparin

In medicine, low molecular weight heparin (LMWH) is a class of medication used as an anticoagulant in diseases that feature thrombosis, as well as for prophylaxis in situations that lead to a high risk of thrombosis.[1] medicines, see medication and pharmacology. ... Oral medication A medication is a licenced drug taken to cure or reduce symptoms of an illness or medical condition. ... An anticoagulant is a substance that prevents coagulation; that is, it stops blood from clotting. ... Thrombosis is the formation of a clot or thrombus inside a blood vessel, obstructing the flow of blood through the circulatory system. ... Prophylaxis refers to any medical or public health procedure whose purpose is to prevent, rather than treat or cure, disease. ...


Heparin is a naturally-occurring polysaccharide that inhibits coagulation, the process whereby thrombosis occurs (see Heparin: Mechanisms of action). Natural heparin consists of molecular chains of varying lengths, or molecular weights. Chains of molecular weight from 5000 to over 40,000 Daltons, making up polydisperse pharmacetical grade heparin.[2] Heparin is a highly sulfated glycosaminoglycan widely used as an injectable anticoagulant. ... Polysaccharides (sometimes called glycans) are relatively complex carbohydrates. ... The coagulation of blood is a complex process during which blood forms solid clots. ... Heparin is a highly sulfated glycosaminoglycan widely used as an injectable anticoagulant. ... The molecular mass of a substance (less accurately called molecular weight and abbreviated as MW) is the mass of one molecule of that substance, relative to the unified atomic mass unit u (equal to 1/12 the mass of one atom of carbon-12). ... The atomic mass unit (amu), unified atomic mass unit (u), or dalton (Da), is a small unit of mass used to express atomic masses and molecular masses. ...


Heparin derived from natural sources, mainly porcine intestine or bovine lung, can be administered therapeutically to prevent thrombosis (see anticoagulation). However, the effects of natural, or unfractionated, heparin can be difficult to predict. After a standard dose of unfractionated heparin, coagulation parameters must be monitored very closely to prevent over- or under-anticoagulation. An anticoagulant is a substance that prevents coagulation; that is, it stops blood from clotting. ...


Low molecular weight heparins (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. They have a potency of greater than 70 units/mg of anti factor Xa activity and a ratio of anti factor Xa activity to anti thrombin activity of >1.5.[3]

Contents

Low molecular heparin products

Various methods of heparin depolymerisation are used in the manufacture of low molecular weight heparin.[4] These are listed below:

  • Oxidative depolymerisation with hydrogen peroxide. Used in the manufacture of ardeparin (Normiflo®)
  • Deaminative cleavage with isoamyl nitrite. Used in the manufacture of certoparin (Sandoparin®)
  • Alkaline beta-eliminative cleavage of the benzyl ester of heparin. Used in the manufacture of enoxaparin (Lovenox® and Clexane®)
  • Oxidative depolymerisation with Cu2+ and hydrogen peroxide. Used in the manufacture of parnaparin (Fluxum®)
  • Beta-eliminative cleavage by the heparinase enzyme. Used in the manufacture of tinzaparin (Innohep® and Logiparin®)
  • Deaminative cleavage with nitrous acid. Used in the manufacture of dalteparin (Fragmin®), reviparin (Clivarin®) and nadroparin (Fraxiparin®)
The anhydromannose in IdoA(2S)-anhydromannose can be reduced to an anhydromannitol
The anhydromannose in IdoA(2S)-anhydromannose can be reduced to an anhydromannitol

Deaminative cleavage with nitrous acid results in the formation of an unnatural anhydromannose residue at the reducing terminal of the oligosaccharides produced. This can subsequently be converted to anhydromannitol using a suitable reducing agent as shown to the left. Certoparin (Sandoparin®, Embolex®, Novartis) is a low molecular weight heparin, primarily active against factor Xa. ... Enoxaparin is a low molecular weight heparin manufactured by Sanofi-Aventis. ... Dalteparin is a low molecular weight heparin. ... Image File history File links Reduction_fig. ... Image File history File links Reduction_fig. ...

UA(2S)-GlcNS(6S)

Likewise both chemical and enzymatic beta-elimination result in the formation of an unnatural unsaturated uronate residue(UA) at the non-reducing terminal, as shown to the left. Image File history File links UA(2S)-GlcNS(6S). ... Image File history File links UA(2S)-GlcNS(6S). ...

Differences between low molecular weight heparin products

Comparisons between LMWHs prepared by similar processes vary. For example a comparison of Dalteparin and Nadroparin suggests they are more similar than products produced by different processes.However comparison of enoxaparin and tinzaparin shows they are very different to each other with respect to chemical, physical and biological properties.


As might be expected products prepared by distictly different processes are dissimilar in physical, chemical and biological properties.


see references.[5][6][7][8][9]


Differences from unfractionated heparin

Its differences with unfractioned heparin include: Heparin is a highly sulfated glycosaminoglycan widely used as an injectable anticoagulant. ...

  • Average molecular weight: heparin is about 20000 Da and LMWH is about 3000 Da
  • Once daily dosing, rather than a continuous infusion of unfractionated heparin
  • No need for monitoring of the APTT coagulation parameter
  • Possibly a smaller risk of bleeding
  • Smaller risk of osteoporosis in long-time use
  • Smaller risk of heparin-induced thrombocytopenia, a feared side-effect of heparin.

The partial thromboplastin time (PTT) or activated partial thromboplastin time (aPTT) is a commonly performed test for the system of coagulation, especially its intrinsic pathway. ... Blood from a finger Bleeding is the loss of blood from the body. ... Osteoporosis is a disease of bone in which the bone mineral density (BMD) is reduced, bone microarchitecture is disrupted, and the amount and variety of non-collagenous proteins in bone is altered. ... Heparin-induced thrombocytopenia (HIT) with or without thrombosis (HITT) is thrombocytopenia (low platelet counts) due to the administration of heparin. ... Heparin is a highly sulfated glycosaminoglycan widely used as an injectable anticoagulant. ...

Clinical uses

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 The partial thromboplastin time (PTT) or activated partial thromboplastin time (aPTT or APTT) is a performance indicator measuring the efficacy of both the intrinsic and the common coagulation pathways. ... A hospital today is an institution for professional health care provided in part by physicians and nurses. ... Deep-vein thrombosis, also known as deep-venous thrombosis or DVT, is the formation of a blood clot (thrombus) in a deep vein. ...


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 who have end stage renal disease. Factor X, also known by the eponym Stuart-Prower factor or as thrombokinase, is an enzyme ( EC 3. ... Chronic renal failure - Wikipedia /**/ @import /skins/monobook/IE50Fixes. ...


Use in venothromboembolic disease associated with cancer

The CLOT study, published in 2003, showed that in patients with malignancy and acute venous thromboembolism, dalteparin was more effective than coumarin in reducing the risk of recurrent embolic events.[10]


Reference

  1. ^ Weitz JI (1997). "Low-molecular-weight heparins". N Engl J Med 337 (10): 688-98. PMID 9278467. 
  2. ^ Linhardt, R.J. Gunay, N. S. (1999). "Production and chemical processing of low molecular weight heparins". Sem. Thromb. Hem. 25 (3): 5-16. 
  3. ^ European Pharmacopedia Commission (1991). "{{{title}}}". Pharmeuropa 3: 161-165. 
  4. ^ Linhardt, R.J. Gunay, N. S. (1999). "Production and chemical processing of low molecular weight heparins". Sem. Thromb. Hem. 25 (3): 5-16. 
  5. ^ Green, D. Hirsh, J. Heit, J. et al (1991). "Low molecular weight heparin: A critical analysis of clinical trials". Pharmacol. Rev. 2: 45-50. 
  6. ^ Barrowcliffe, T. W. (1995). "Low molecular weight heparin(s)". Br. J. Haematol. 90: 1-7. 
  7. ^ Donayre C. E. (1996). "Current use of low molecular weight heparins". Semin. Vascul. Surg. 9: 362-371. 
  8. ^ Hunt, D. (1998). "Low molecular weight heparins in clinical practice". Southern Medical J. 91: 2-10. 
  9. ^ Fareed, J. Jeske, W. Hoppensteadt, D. Clarizio, R. Walenga, J. M. (1998). "Low molecular weight heparins: Pharmacologic profile and product differentiation". Am. J. Cardiol. 82: 3L-10L. 
  10. ^ Lee AY, Levine MN, Baker RI, Bowden C, Kakkar AK, Prins M, Rickles FR, Julian JA, Haley S, Kovacs MJ, Gent M (2003). "Low-molecular-weight heparin versus a coumarin for the prevention of recurrent venous thromboembolism in patients with cancer". N Engl J Med 349 (2): 146-53. PMID 12853587. 

  Results from FactBites:
 
LMWH (348 words)
Low Molecular Weight Heparins are shorter chains of unfractionated heparin.
Low molecular weight heparin also may cause this, however it is suspected that the risk of this is much less than with unfractionated heparin.
Even though low molecular weight heparin is administered at home by injection instead of in the hospital by vein, the effect on clotting elements is similar and the risk of bleeding persists.
Low molecular weight heparins in medicine and anaesthesia (2719 words)
LMWH is produced by either chemical or enzymatic depolymerization of SH and has a mean molecular weight of 4000–6500 Daltons and a chain length of 13–22 sugars.
Low Molecular Weight Heparins (LMWH) are at least as effective as unfractionated heparin (UFH) in the prevention of deep venous thrombosis and subsequent embolism.
LMWH are associated with an increasing incidence of spinal haematoma in patients undergoing neuraxial anaesthesia, particularly epidurals.
  More results at FactBites »

 
 

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