Coags Flashcards
What happens with platelets when they encounter endothelial injury?
They stick to the subendothelial collagen matrix, release thromboxane A2, causing other platelets to adhere and degranulate
Factors released by degranulation of platelets
Serotonin and histamine (vasoconstriction)
TXA2 (causes aggregation and degranulation of platelets)
ADP (activates the GP IIb/IIIa binding site, making the platelet more sticky)
Clotting factors 5, 8, 9
Platelet Factor 4 (heparin neutralizing factor-enhances clotting)
Fibrinogen (links platelets)
End product of the coagulation cascade
Fibrin
The intrinsic pathway is measured by ____ and the extrinsic is measured by ______
PTT
PT
Examples of natural anticoagulents that our bodies make
Prostacyclin II
Antithrombin II
Heparin
Proteins C and S
Remember that coagulation is a balance in our bodies. There are constantly micro-clots being formed as endothelial damage occurs. We need natural anticoagulents to make sure that we’re just making clots all the time.
Examples of oral antiplatelet meds
ASA (COX inhibitor) Ticlopidine Clopidogrel (Plavix) Prasugrel Ticagrelor
IV antiplatelet meds
Abciximab
Eptifibatide (Integrellin)
Tirofiban
All of these work by inhibiting GP IIb/IIIa
How does ASA work?
It’s a COX inhibitor. It prevents the formation of thromboxane A2, which decreases platelet aggregation and degranulation)
In general, what are antiplatelets used for?
For the prevention of recurrent ischemic events (stroke, MI)
Precautions associated with ASA
Children (Reye’s syndrome)
Pregnancy (placental bleeding)
Increases leukotriene production (risk for asthmatics)
Decreases effectiveness of ACE inhibitors, B-blockers, and diuretics
How do the oral antiplatelets work (excluding ASA)?
They block the ADP receptor. Normally, binding of ADP causes GP IIb/IIIa activation and formation of fibrinogen links between platelets.
When might you use ticlopidine (Ticlid) instead of ASA?
ASA intolerance
However, ticlopidine (Ticlid) is rarely used because it can cause neutropenia and thrombotic thrombocytopenic purpura (TTP)
When must clopidogrel be stopped before surgery?
At least 5 days prior.
Which is better for monotherapy, ASA or plavix?
Plavix. However, ideal is dual therapy with ASA.
People who are genetically predisposed not to respond to plavix will be placed on
Prasugrel
Prasugrel compared to plavix
Prasugrel works better than plavix, but it’s expensive and has higher risk of fatal events. Risk of bleeding is 4x higher than plavix