Thrombosis + platelet pharmacology Flashcards
What is the difference between haemostasis and thrombosis?
Haemostasis= appropriate coagulation thrombosis= inappropriate coagulation
Primary haemostasis- factors involved and treatments
factors- platelet VWF treatments 1. platelet transfusion 2. desmopressin 3. VWF concentrate
Secondary haemostasis- factors and treatments
factors- clotting factors
treatment- specific to clotting factor
Thrombosis can be either
Arterial or venous
Arterial thrombosis
Factors- high pressure platelets
treatments- antiplatelet drugs
Venous thrombosis
factors- low pressure clotting factos
treatments- anti-coagulants
Different components of blood
- platelets
- fresh from frozen plasma- factors 1, 7 9 ,VWF, 9,10,11,12
- red cells
Why couldn’t you just give plasma if someone was bleeding?
Contains lots of clotting factors
However
not dilute
could get infection
Coagulation cascade
Vessel injury- local vasoconstriction
then either:
1. platelet adhesion- platelet aggregation
2. activation of coagulation cascade- fibrin formation
Haemostatic plug
fibrinolytic activity and repair vessel damage
Primary haemostasis mechanism
- expose collagen
- platelet stick to collagen by VWF factor and activate other factors
- open confirguation and binds to platelets to form plaque by sticking on top of each other
Platelet disorder bleeding- why?
- reduced number- inherited or acquired- thrombocytopenia
2. abnormal or reduced function of platelets- could be due to anti-platelet drugs
What is a treatment for platelet disorder?
platelet transfusion
What is Von Willebrand disease?
Commonest inherited bleeding disorder
1% population have reduced VWF levels
autosomal dominant- 3 main types
milder bleeding disorder than haemophilia
Sites of bleeding in von Willebrand disease?
bruising, cuts, gums, epistaxis, menorrhagia
post operative, post trauma
treatment for von Willebrand disease?
desmopressin- protein release vmf into the circulation
intermediate purity- VMF and powder mix with water for injection 1:1 (VMF: factor 8)
Secondary coagulation cascade
TF/VILa to either X or IXa (back to X by VIII)
from X to Xa
Xa to il
il to ILa which changes fibrinogen to fibrin (mesh will work/ stop things from working)
What inhibits IXa, Xa and iLa?
unfractionated heparin
low mol WT heparin
Analogy for stopping bleeding
Hole in vessel= pipe you have to plug either 1. band aid to plug - platelets -more you have the closer together the more it stops bleeding 2. spray with super glue= 2nd
What are coagulation factor disorders?
haemophilia A- factor 8 defiecency
haemophilia B- factor 9 deficiency
others- autosomal recessive, deficiency in fibrinogen, FII FV FVII FX FXI FXII
Sites of bleeding for haemophilia A/B?
joints, muscles , post trauma , post operative
Severity of haemophilia
severe <1%
moderate 1-5%
mild >5%
Haemophilia
don’t have bleeding mucosal so just get bleeding from the joints from operations
bleed from joints- lots of damage to knee- painful- joint replaced
- haemoarthosis/ muscle atrophy
- muscle haematoma- IM injection in haemophilia
Clotting factors
- All plasma derived
- some recombinant- cell line have gene- 8,9,13
rare so other companies wouldn’t invest
Treating with clotting factors
give to plasma to replace all- dilute form
can give specific if you know what is missing
What is thrombosis?
- blood in blood vessels should be fluid
- inappropriate blood coagulation within a vessel
What are the 2 types of thrombosis
- arterial= high pressure, platelet rich
2. venous = low pressure, fibrin rich
Clinical thrombosis implications
- myocardial infarction, thrombotic stoke
2. leg deep vein thrombosis (DVT) or pulmonary embolism (PE)
Treatment for thrombosis
- antiplatelet drugs- aspirin, clopidogrel, prasugrel, ticagretor, cangregor
- anti-coagulation drugs-
Intravenous= unfractionated heparin
subcutaneous= low molecular weight heparin
Oral= warfarin, dabigatixin, rivaoxoban, apixoban
Oral anticoagulant
Vit K anticoagulants
96% warfarin
4% acenoncoumarol
Direct oral anti-coagulants
dabigatran
apixoban
rivaoxaban
edoxoban
What is heparin?
Protein in blood antithrombin and its role is to inhibit different parts of the coagulation cascade
activates antithrombin
given continuously by infusion
Heparin mechanism?
binds to antithrombin and increases its activity
indirect thrombin inhibitor
How do you monitor heparin?
APPT test
What is low molecular weight heparin?
Smaller molecular made from heparin less variation in dose weight adjusted dosing given subcutaneously, given once a day renally excreted
Disadvantages of low molecular weight heparin?
Pain to use- continuous infusion
The pharmacology of warfarin?
given by mouth completely and rapidly absorbed
99% plasma protein bound
inhibit II, VII, IX, X production
- peak effect 3-4 days after and still present in 4-5 days after
Side effects of warfarin>?.
bleeding
embryopathy
Monitoring Warfarin
Measure INR- international normalised ratio
dose is based on INR
target for first DVT/PE- 2-3.0
frequency of monitoring depends on stability of patients INR
Dose of warfarin
no single dose for one person
avg 5mg/day
Genetically controlled
all body makes clotting factor
Oxidised vitamin K to reduced Vit K
Vit K reductase
which is inhibited by warfarin
functional
What turns warfarin from active to inactive metabolite
CYP2C9- breaks down warfarin
Reduced Vit K to oxidised Vitamin K
hypofunctional to functional carboxylated
by gamma-glutamyl carboxynase GCX
Vit K + enzyme =
makes functional carboxylated
Vit K is recycled so not deficient and warfarin inhibits this recycling of Vit K- becomes deficient (anticoagulant )
Why do different people have different doses?
People breakdown warfarin at different speeds= different polymorphisms
so people very receptive by VKOR
1. how receptive
2. how quickly you breakdown
What replaces heparin and warfarin? and why?
the direct oral anticoagulant
Why- oral, no monitoring, standard dosing, short half life, no alcohol/ food interactions
problems= expensive
What inhibits Xa
Rivaroxaban- 2-3hours work,67% effect, 95% protein binding
Apixaban- 3-4 hours work, 25% effect, 87% protein binding
Edoxaban- 1-3 hours, 35% work, 50% binding
not licensed yet but undergoing trials
inhibition of Ila
Dabigatran- 2-3 hours work, 80% effect, 35% protein binding
licensed
What are all the new drugs positive for
AF DVT PE none for general thromboprophylaxis all but edoxaban pos for orthopaedic thromboprophylaxis
Compare advantages of DOAC to warfarin
Advantages
- rapid onset
- fixed oral dosing
- low interaction with food/ alcohol
- no need for blood monitoring
Disadvantages
- renal elimation
- no specific antibodies for Xa inhibitor
- licensed for only specific introduction
- recent
Key phases of drug development
identify drug target design and optimise drug preclinical trial- proof it works in vivo- efficacy, toxicity Phase 1 - first in man Phase 2- small scale Phase 3- large scale= safe and efficacy
How atheromas are formed and problem with them
normal- fatty streak- fibrous plaque- atherosclerotic plaque- plaque rupture/fissure and thrombosis
leads to:
Stoke, MI, critical leg ischaemia, CVD
What does organised atherothrombosis look like?
extensive atherosclerotic plaque
organised thrombosis
vascular channel with thrombus potential blood flow through new vascular channels
Platelet shape change with activation
smooth discoid- spiculated and pseudopodia
increase SA
increases the possibility of cell-cell interactions
Glycoproteins Ila/ilb receptor- Where are they and what are they for?
On the surface of the platelet- 50,000- 100,000 copies on resting platelet
Help with platelet aggregation- increases with increase in number of receptor, affinity of receptor for fibronegin increase
What does fibrinogen do?
Links receptors binding the platelets together
known as integrin AilaB3
Glycoprotein Ila/Ilb antagonists
Intravenous only
drugs- abciximob, tirofiban, epitifibatide
block the Ila/b receptor
Risk and benefits of Glycoprotein Ila/Ilb antagonists
Risk- increase risk of major bleeding
benefit- reduces ischaemic events
Therapeutic window for Glycoprotein Ila/Ilb antagonists
not effective at low dose
too much and bleeding will kill
explains why clinical development of oral antagonists failed
What is aspirin?
Effective antiplatelet drug with limited inhibitory effects
Cylooxygenase 1 and 2 pathway
Membrane phospholipid to arachidonic acid then either to Cyclooxygenase 1 or 2
1- Gi mucosal integrity, platelet aggregation and renal function
2- mitogenesis and growth, regulation of female production, bone formation, renal function
What is the effect of aspirin on platelets?
- Aspirin blocks COX1 by irreversibly acetylating the enzyme
- effects lost the lifetime of the platelet
- Prevents conversion of arachidonic acid to prostaglandins H, blocks the pathway that leads to platelet thromboxane A release
- thromboxane A activates platelet via a surface receptor
What is aspirin resistance
Continued secretion of thromboxane A2 by platelets in response to appropriate agonist stimulation (such as A collagen) despite therapy with aspirin at a standard dose
*high platelet reactivity despite aspirin therapy does not necessarily equate to this
True aspirin resistance
Rare
- fontanna et al 2006- 96 healthy volunteers, aspirin 100mg/day for 7 days
1 subject= complete suppression witnessed after loading course of 300mg
What induced platelet aggregation in 190 IHD patients?
Arachnoid acid
Impairment of effects of aspirin due to reversible COX1 inhibition by ibuprofen
- Thromboxane B2 % inhibition was halved after 24 hours when ibuprofen was given before aspirin
- when rofecoxib was given before aspirin there was no change in % inhibition for 12/24 hours after comparing aspirin
What does this paper show- “ expert position paper on the role of platelet function testing in patients undergoing percutaneous coronary intervention”
Current evidence doesn’t support the prognostic screening for aspirin in response after PCI
Aspirin show be given at low doses and platelet function testing to adjust dosing is not recommended
Conclusions about aspirin
reduces risk of MI, Stoke and CV
excellent efficacy at inhibiting platelet thromboxane A2 release
patient compliance is key
What else could be used as a potential drug target
platelet purinergic receptor (P2)
What does targeting P2Y1, P2Y12 and P2X do~?
P2Y1= inhibition of platelet aggregation shape change P2Y12= amplification of platelet activation/ aggregation, amplification of granule release and procoagulant activity P2Xi= shape change, amplification of platelet activation
P2Y12 role in platelet activation
Unlike the other P receptors
it activates Platelet aggregation
Mean thrombus area in P2Y12 mice
laser injury of cremasteric arteriole with fluroesence imaging followed by IV DIOC injection
+/+= area is consistent
-/-= area decreases over time
Activation/ inactivation of clopidogrel
Clopidogrel-(cyp)- 2-Oxo-clopidogrel - R-130964
clopidogrel by esterase to SR26334
2-oxo-Clopidogrel by esterase to inactive
CURE study outcomes
clopidogrel plus aspirin vs aspirin alone In ACS patients
Clop- decreased% of CV/MI/Stroke but everything else else was not significantly different
What is associated with impaired clopidogrel response
Diabetes mellitus
What increased clopidogrel active metabolite production
Rifampicin
Clopidogrel and rifampician effect on P2Y12 receptor blockade
has no effect
Loss of function allele in CYP2C19 is associated with what?
Stent thrombosis in clopidogrel treated patients
relationship between verify now p2y12 PRV and stent thrombosis within 30 days
- definite or probable
Factors affecting response to clopidogrel
dose age eight disease states drug - drug interaction CYP2C19 loss of function or gain of function
Prasugrel
A more effective thienopyridine prodrug than clopidogrel
prasugrel by esterase- R-95913 by CYP - R-138727
Healthy volunteer study with clopidogrel and prasugrel crossover
Measured active metabolite by LC/MS
Clopidogrel stops over time
prasugrel plasma conc decreases over time
The triton- time 38 study design
Acute coronary syndrome and planned percutaneous coronary intervention
double blind
clopidogrel= 300mg/day
prasugrel= 60mg/day
Endpoints got titron study
1ST- cv death/MI/ stroke
2nd- CV/ MI/ stroke/ Isch/stent thrombosis
safety endpoint- TIMI major bleeds, life threatening bleeds
Results from Titron
Clopidogrel reduced for all- timi bleed, life threatening, non fatal and fatal
What is ticagrelor
the first oral reversibly binding platelet P2Y12 antagonist belonging to the class CPTP
Pre clinical studies for ticagrelor
effect of tricagrelor on thrombus formation
laser injury model- mean thrombus area
- decrease thrombus in -/- mice same as treated
Phase 2 study ticagrelor
Moderate to high risk patients with ACS
2 groups- ACS with clopidogrel and ticagrelor
12 month max exposure
results of ticagrelor
ticagrelor had a lower incidence of MI and stroke over time
Benefits of using ticagrelor compared to clopidogrel?
Cost effectiveness
PEAGUSUS-TIMI 54 study design
Stable patients >50 years old with history of MI
1-3 years prior>1 additional atherothrombotic risk factor
randomised, double blind
3 different 3 different ticagrelor- 90mg, 60mg, placebo
Results
41% and 31% TIMI bleeding- 90mg and 60mg
Recommendations from the clinical trial
- P2Y12 inhibitor in addition to aspirin- 12 months unless contradictions
- ticagrelor 180mg twice daily- patients with moderate to high ischeamic events
- prasugrel- 10mg daily- patients with PCI
- clopidogrel- 300-600mg loading (cannot receive with the 2 ^)
Short and long term treatment
short term- P2Y12 inhibitor for a short duration of 3-6 months after DES implantation may be considered in patients deemed high bleeding
long term- P2Y12 inhibitor + aspiring = after careful assessment of ischaemic and bleeding risks
General recommendations
proton pump inhibitor
combo with DAPT for people with increased risk of of GI bleeds
Conclusions
Aspiring= effective but weak antiplatelet drug targeting platelet COX1
Platelet P2Y12 receptor= key role in platelet formation, these plus aspirin are the mainstay treatment
clopidogrel= decrease risk of clinical event with arterial thrombosis , variety of response due to efficacy
prasugrel= more effective than thienopyride
ticagrelor= oral P2Y12 antagonist, reduces MI and Stroke
