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| {{SI}}
| | #REDIRECT [[Heparin#Pharmacology]] |
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| ==Overview==
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| ==Mechanism of action==
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| * [[Heparin]] is an [[indirect thrombin inhibitor]].
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| * It forms a complexes with [[antithrombin]] / AT III (predominantly) and other factors like factor Xa, factors XIIa, XIa, and IXa, that results in a conformational change in [[antithrombin]], converting it from a slow to a rapid inactivator of [[thrombin]].
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| * Antithrombin has two active sites:
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| ** Reactive center, Arg393-Ser394
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| ** Heparin binding sites
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| The unfractionated heparins have long saccharide units that are lacking in in the low molecular weight (LMW) heparins, and fondaparinux. These long chains of polysaccharides are required for heparins to bind to both AT and to a binding site on thrombin and formation of a tenary complex. Accordingly, LMW heparins and fondaparinux have less antithrombin activity than does unfractionated heparin [8,9].
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| * Direct binding to platelets
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| * Binding to heparin cofactor II (high concentrations) .
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| {{WH}}
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| {{WS}}
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