Anticoagulation Flashcards
drugs used in coagulation disorders
Antiplatelets
anticoagulants
thrombolytics
coagulants
role platelets play in homeostasis
They arrest bleeding from a damaged BV
What happens when a BV is injured?
Exposure of the materials inside the BV will act as a catalyst to kick off a number of processes that lead to plugging the hole. BV constricts and platelet aggregation occurs.
platelets are derived from
megakaryocytes, they have no nucleus
What are the 3 steps to thrombus formation?
Adhesion and shape change
secretion
aggregation
The adhesion step of thrombus formation is driven
The presence of collagen behind the endothelial layer of the BV
WHat happens when there is damage to the endothelium
Platelets and clotting factors will find things that they normally do not see (collagen), kicking off coagulation.
Exposure of platelets to what will allow platelets to adhere to collagen
VWF (vonwillebrand factor)
What does GP1a bind? What does GP1b bind?
GP1a binds collagen
GP1b binds VWF
How do endothelial cells inhibit platelet aggregation?
Prostacyclin (PGI2) is secreted to inhibit platelet aggregation
PGI2 also causes vasodilation
What happens when we have damage to the endothelial layer
We lose the ability to locally inhibit platelet aggregation and lose the ability to locally cause vasodilation
What is the 2nd step of platelet aggregation called?
secretion
Platelets adhere to damaged portion of BV through
GP1a and GP1B
What things are secreted after the adhesion of platelets
Platelets undergo degranulation and secrete ADP, thromboxane A2 (TXA2) and serotonin, which are pre-stored in platelet
WHat do the secreted factors from platelet do?
These factors bind to receptors on other platelets and recruit these platelets to site of damageWhich factors are potent vasoconstrictors
Thromboxane A2 and Serotonin
degranulation leads to secretion of
ADP, txA2 and serotonin.
These bind to other platelets
What receptor is an important pcol target to prevent platelet aggregation
ADP receptors
TXA2 stimulates
recruitment of platelets to site of damage
what is the final step in platelet aggregation
Platelatelet aggregation
What happens to platelets in platelet aggregation phase
Platelets undergo a shape change that activates their GP IIb/IIIa receptor.
What factors activate GP IIB/IIIa receptors
They are activated by the stimulation of ADP, TXA2 and serotonin, They can crosslink platelets to each other.
What is fibrinogen? what does it do?
Fibrinogen crosslinks platelets via fibrinogen binding to its BIVALENT receptors
What happens after platelets are cross linked by fibrinogen?
They fuse together and compact around site of damage. This becomes the substrate for formation of fibrin clot.
WHat are some targets to inhibit platelet aggregation?
Inhibit GP IIb/IIIa receptors, TXA2, ADP receptors or inhibit thrombin
WHat are some drugs that have actions related to platelets
COX-1 inhibitors, ADP receptor inhibitors, PDE 3 inhibitors, protease activated receptor inhibitors
What does aspirin (ASA) inhibit
COX-1 (covalently)
How does aspirin interfere with platelet aggregation? what effects will that have on the body? WHat is its use?
inhibits TXA2 production. Prolongs bleeding time. Prevents arterial thrombin formation
Dose of aspirin that is used to inhibit platelet selectivity? Why this specific dose?
50-320 (81mg). At this dose, it leaves the prostacyclin production in endothelium alone and selectively inhibits thromboxane A2 production
What is produced by COX2
PHI 2 (prostacyclin)
indication of aspirin
prophylaxis and tx of arterial thromboxane disorders
prevents thrombosis in unstable angina
Can be used with thrombolytic therapy
Prevents recurrence of strokes
Side effects of aspirin
prolongs bleeding
GI bleeding due to cox-1 ihibition (increased risk of this in in NSAID pts)
WHat does COX 2 pruduce and what is its use?
Produces prostaglandin in endothelial cells. Vasodilation and inhibiton of platelet aggregation
What does COX 1 produce? What is its use?
Produces thromboxane A2 in platelets. Used for vasoconstriction and platelet aggregation.
What do selective COX 2 inhibitors do? what effect does this have?
They block synthesis of prostacyclin in endothelial cells, while not blocking TXA2. This leads to pro-platelet aggregation, increasing CV events.
What is the name of the two adp receptors involved in activating platelets
P2Y1
P2Y12
what receptors are P2Y1 and P2Y12 coupled to
P2Y1- GQ
P2Y12- Gs
How does P2Y12 work?
it inhibits adenylyl cyclase
What are drugs that target this receptor
Prasgurel, clopidogrel, ticagrelor, cangrelor
WHat is the difference between the drugs that target P2Y12?
Prasgurel and clopidogrel undergo metabolism to active form (prodrugs) and are irreversible, while ticagrelor and cangrelor do not require activation and are reversible
What happens when we block P2Y12
Prevents platelet aggregation
Clopidogrel binds to? MOA?
binds to p2Y12. It is a prodrug that irreversibly blocks ADP receptors, inhibiting platelet activation.
Clopidogrel duration of action? indication?
Long duration of action.
prevention of heart attack, stroke, peripheral vascular disease
What kind of drugs are clopidogrel and prasgurel?
Theinopyridine drugs (they are also prodrugs)
How is prasgurel activated?
Activated by esterase-1 CYP 3A4/2B6
prasgurel warnings
Old people can not use it due to risk of bleeding
Which P2Y12 drugs are reversible
Ticagrelor and cangrelor, they also have a short t1/2
Ticagrelor is a substrate for____
Onset and duration?
CYP3A4.
Fast onset and short half life
What is cangrelor used for
Used to prevent thrombosis during PCI
It is reversible, fast onset, short t1/s
Clopidogrel is activated by
CYP2C19
prasgurel needs _____ to cleave its bonds
esterase
What happens to prasgurel in the active form
The drug binds P2Y12 receptor and forms a disulfide cross link, becoming irreversible
What does dipyridamole do?
Inhibits PDE III in platelets and acts as aggregation inhibitor
dipyridamole can be used in conjuction with______ and ______ to prevent thrombosis
Warfarin and aspirin
What does citazole do?
Also a PDE III inhibitor. Used in a condition called intermittent claudification.
What does fibrinogen bind to? What does it do once bound?
Binds to GP IIb/III a to crosslink adjacent platelets
What do GPIIb/IIIa inhibitors do?
They inhibit the ability of fibrinogen to crosslink the platelets
Name GP IIb/IIIa inhibitor drugs
Abiciximab
Eptifibatide
tirofiban
All of the GPIIb/IIa drugs ROA, they are all used in conjuction with
All IV
In conjuction with PCI
What type of molecule is eptifibatide
Cyclic peptide
What does Eptifibatide do?
Inhibits fibrinogen binding to decrease platelet aggregation
Eptifibatide MOA
arginine (R), glycine (G), aspartic acid (D) motif is the basis of binding, which exists in fibrinogen to bind GPIIB/IIIA. So it is a perfect mimic
What kind of molecule is tirofiban
small molecule
MOA of tirofiban
R,G,D motif that acts as a mimic to bind to gPIIb/IIIa
tirofiban can be compined with____
heparin to treat acute coronary syndrome
What kind of drug is abriximab
Antibody
What is an important thing about abciximab that we should know
long duration of action, increased risk of bleeding
Abciximab MOA
Binds to GPIIb/IIIa and inhibits platelet aggregation
What are eptifibatide, tirofiban,abciximab indicated for?
all given IV for unstable angina and stents to prevent thrombosis
What does thrombin do?
activates platelets
how does thrombin activate platelets
Via protease activated receptor (PAR)
MOA of thrombin on platelets
proteolytic cleavage of PAR-1 on platelet surface
PAR is activated by
thrombin
why is cox 1 targeted in antiplatelet drugs
cox 1 synthesizes txa2,
why is GPiib/iiia a target for antiplatelet activity
fibrinogen (protein that is cleaved to generate a fibrin clot) is bivalent and binds to two GPIIb/IIIa receptors to crosslink platelets. we can inhibit cross linking of platelets by targeting GPIIb/IIIa
why is P2Y12 a target for antiplatelet activity
It secretes ADP, stopping this can inhibit aggregation
what does thrombin do?
cleaves fibrinogen to fibrin.
activates PAR
How does thrombin activate platelets
cleavage of PAR-1 receptors on platelet surface
Vorapaxar MOA
inhibits I/A of thrombin with PAR, inhibits thrombin activation of platelet aggregation
is vorapaxar reversible?
yes
Know structures of the drugs