Heparina: Diferenzas entre revisións

A heparina e os seus derivados de baixo peso molecular (como a [[enoxaparina]], [[dalteparina]], [[tinzaparina]]) son efectivos na prevención das tromboses das veas profundas e embolias pulmonares en pacientes de risco,<ref>{{cite journal|author=Agnelli G, Piovella F, Buoncristiani P, ''et al.''|title=Enoxaparin plus compression stockings compared with compression stockings alone in the prevention of venous thromboembolism after elective neurosurgery|journal=N Engl J Med|year=1998|volume=339|issue=2|pages=80–5|pmid=9654538|doi=10.1056/NEJM199807093390204}}</ref><ref>{{cite journal|volume=346|pages=975–980|year=2002|issue=13|title=Duration of prophylaxis against venous thromboembolism with enoxaparin after surgery for cancer|author=Bergqvist D, Agnelli G, Cohen AT, ''et al.''|url=http://content.nejm.org/cgi/content/abstract/346/13/975|journal=N Engl J Med|doi=10.1056/NEJMoa012385|pmid=11919306}}</ref> pero non hai evidencia de que algún deles sexa máis efectivo ca o outro na prevención da mortalidade.<ref>{{cite journal|author=Handoll HHG, Farrar MJ, McBirnie J, Tytherleigh-Strong G, Milne AA, Gillespie WJ|title=Heparin, low molecular weight heparin and physical methods for preventing deep vein thrombosis and pulmonary embolism following surgery for hip fractures|journal=Cochrane Database Syst Rev |year=2002 |volume=4 |pages=CD000305 |doi=10.1002/14651858.CD000305 |pmid=12519540 |issue=4}}</ref> A heparina únese ao [[inhibidor encimático]] [[antitrombina]] III causándolle un cambio conformacional, que o activa ao incrementar a flexibilidade do bucle do seu [[sitio activo]].<ref>{{cite journal | author = Chuang YJ, Swanson R. ''et al.'' | title = Heparin enhances the specificity of antithrombin for thrombin and factor Xa independent of the reactive center loop sequence. Evidence for an exosite determinant of factor Xa specificity in heparin-activated antithrombin | journal= J. Biol. Chem. | year= 2001 | volume= 276 | issue= 18 | pages= 14961–14971 | pmid = 11278930 | doi = 10.1074/jbc.M011550200}}</ref> A antitrombina activada actúa sobre a [[trombina]] inactivándoa e sobre outras [[protease]]s implicadas na [[coagulación do sangue]], principalmente sobre o [[factor Xa]]. O grao de inactivación destas proteases causado pola antitrombina pode aumentar ata 1000 veces debido á unión da heparina.<ref>{{cite journal | author = Bjork I, Lindahl U. | title = Mechanism of the anticoagulant action of heparin | url=http://www.springerlink.com/content/g67115564280w013/ | journal=Mol. Cell. Biochem. | year=1982 | volume=48 | pages=161–182 | doi = 10.1007/BF00421226 | pmid = 6757715 | issue = 3}}</ref>