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| {{SI}}
| | #REDIRECT [[Heparin#Pharmacology]] |
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| ==Overview==
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| [[Heparin]] is an [[indirect thrombin inhibitor]]. It's [[anticoagulation]] effects are due to activation of [[antithrombin III]], that in turn inactivates [[thrombin]] (factor IIa) and [[factor Xa]]. The other minor mechanism of benefits are due to its inhibition of [[platelet]] aggregation. | |
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| ==Mechanism of action==
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| * [[Heparin]] is an indirect [[thrombin inhibitor]]. It has its effects through the following mechanisms-
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| ** It forms a complex with [[antithrombin]] / AT III that results in a conformational change in [[antithrombin]], converting it from a slow to a rapid inactivator of [[thrombin]]. It also inactivates other factors like factor Xa, factors XIIa, XIa, and IXa.
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| ** [[Antithrombin]] has two active sites: reactive center, Arg393-Ser394 and heparin binding sites. The unfractionated heparins have long saccharide units that are lacking in in the [[low molecular weight heparins]] (LMW), 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.
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| ** Direct binding to platelets
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| ** Binding to heparin cofactor II (high concentrations) .
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