Anti Platelet Agents

Physiology and Pathology of Platelet Aggregation, Anti Platelet Agents, Relevant Clincal Trial Data

1. Anti Platelet Agents

2. Pathophysiology of the Thrombus

7. Platelet-fibrin clot

8. Wagner DD. Arterioscler Thromb Vasc Biol. 2005;25:1321-4.
Interaction between
inflammation and hemostasis in
vulnerable plaque

9. Platelet Activation Pathways
Arachidonic
acid
TxA
2
GP IIb/IIIa
Epinephrine
Collagen
Thrombin
ADP

10. Endothelial Cell/Monocyte
PLATELET RECRUITMENT
AA
PGH
2
COX –1
COX-2
ASA
COX-2 induced by
shear stress and
inflammation PGH
2
TXA
2
PGG2

11. Targets for anti-platelet therapy
Aspirin
NSAIDs
ADP
receptor
COX-1
TXA2
GPIIb-IIIa
Signalling
pathways
ADP receptor
antagonists
Clopidogrel
THROMBIN
receptor
Thrombin
inhibitors
II
F
i
b
r
i
n
o
g
e
n
Phosphodiesterase
inhibitors
dipyridamole
Fibrinogen Receptor
Antagonists
AAAA

12. Curran MP, Keating GM. Drugs. 2005;65:2009-35.
Thrombolytics
Abciximab
Tirofiban
Eptifibatide
UFH
LMWHs
Direct thrombin
inhibitors
Aspirin
Thromboxane
A
2
Collagen ADP Thrombin
Fibrinogen
Fibrin
GP IIb/IIIa activation
von Willebrand factor
Platelet aggregation
Thrombus formation
Ticlopidine
Clopidogrel
Points of action for
antithrombotics

14. Resting
platelet
GP IIb/IIIa
receptors in
unreceptive
state
Inhibition of platelet
aggregation
GP IIb/IIIa receptors occupied
by antagonists
Agoni
st
ADP,
thrombin,
collagen
GP
IIb/IIIa
antagoni
st
Fibrinoge
n
Aggregating
platelets

15. ASPIRIN
1832 Felix Hoffmann produced acetylsalicylic acid.
1899 Bayer distributed aspirin to physicians.
1915 Aspirin available without prescription.
1953 Dr. Lawrence Craven observed aspirin prevented
heart attacks in 400 patients prescribed aspirin.
1988 FDA approved aspirin for Secondary MI prevention.
2002 AHA and US Preventative Services Task Force recommends aspirin to prevent first MI in at-risk
individuals.
2004 Over 26 million Americans use aspirin routinely to
reduce heart attack risk.
2005100 Billion Aspirin consumed per year.

16. Mechanism of Action of Aspirin
Platelet Recruitment
TXA
2
AA
PGH2
COX-1
PGI
2
ASA (low dose)
Endothelial Cell
(temporary)
Platelet
(permanent)

17. Platelet cyclooxygense -1
Catalytic site
Serine res
529
Arachidonic acid
PGG2
With Aspirin
Acetyl
serine
Aspirin
Platelet
TXA2
PGH2

18. Aspirin and COX-2
•Aspirin also inactivates COX-2 (PGH-2-synthase) but is 50 to
100 times less potent at inhibiting COX-2 than COX –1.
•COX-2 is induced in monocytes in response to inflammatory
stimuli and in endothelial cells in response to shear stress.
•COX-2 is present in megakaryocytes and young platelets, but not
in mature platelets.
•COX-2 is not inhibited by low “antithrombotic” doses of aspirin.

19. Definition of Aspirin Resistance
•Clinical event despite taking aspirin
•Failure to show adequate level of platelet inhibition
•Failure of low dose aspirin to inhibit a test of platelet
function that can be inhibited by higher doses of
aspirin
•Generation of thromboxane A
2
despite treatment with
aspirin

20. Definition of Aspirin Resistance
Clinical event despite aspirin
•ASA produces a 25% risk reduction, therefore
75% of patients with vascular disease ‘fail’
•Not surprising because ASA only inhibits one of
a number of mechanisms of platelet activation

21. Aspirin Resistance
•10% - 40% of patients appear to be resistant
•Variability due to several factors:
–Method of measuring platelet function
–Clinical status of patients
– Conclusion
Aspirin resistance exists!
Aspirin resistance is measurable!
-pharmcodynamically & clinically
Aspirin resistance has clinical consequence!

22. COX (cyclo-oxygenase)
ADP (adenosine diphosphate)
TXA
2
(thromboxane A
2
)
CLOPIDOGREL
ASA COX
ADP
ADP
C
GPllb/llla
(Fibrinogen receptor)
Collagen thrombin
TXA
2
Activation
TXA2
Mode of Action of Clopidogrel
1
1. Jarvis B, Simpson K. Drugs 2000; 60: 347–77.

23. Effects of ADP-Receptor
Activation
Adapted from Savi P et al. Biochem Biophys Res Commun 2001; 283: 379–83, and Ferguson JJ.
The Physiology of Normal Platelet Function. In: Ferguson JJ, Chronos N, Harrington RA (Eds).
Antiplatelet Therapy in Clinical Practice. London: Martin Dunitz; 2000: pp.15–35.
ADP / ATP
P2Y
1
P2X
1
P2T
12
Gi
2
coupled
Gq coupled
Ca
2+
Ca
2+
cAMP
Platelet shape change
Transient aggregation
No effect on
fibrinogen
receptor
Cation influx Calcium mobilization
Fibrinogen receptor activation
Thromboxane A
2
generation
Sustained aggregation response

24. A Loading Dose of Clopidogrel
Provides Rapid and Full Effect by
3 Hours
1
1. Data on file, Sanofi-Synthélabo, 1999, internal report PDY 3494.
100
-20
0
20
40
60
80
1.5 3 6 24 27 48
Time (hours)
M
e
a
n

i
n
h
i
b
i
t
i
o
n

(
%
)
Clopidogrel
75 mg
Clopidogrel
300 mg
*
*p < 0.002 vs clopidogrel 75 mg
(n = 20/group)
*
*
*
*
*
Healthy Volunteers

25. Effects of Clopidogrel on a Key
Inflammatory Modulator
(CD40L)
1
1. Hermann A et al. Platelets 2001; 12: 74–82.
Effects ex vivo in healthy volunteers
*p < 0.05 versus ADP-stimulated controls
0
0.1
0.2
0.3
0.4
0.5
Control ASA Clopidogrel Clopidogrel
plus ASA
C
D
4
0
L

(
M
n

X
)
*
*
Control
ADP, 30µM

26. Effects of Clopidogrel on Platelet-
Dependent Mitogenesis of Smooth
Muscle Cells
1,2
1. Hermann A et al. Thromb Res 2002; 105: 173–5. 2. Hermann A et al. Arch Pharmacol 2001;
363(suppl 4): 442.
*p < 0,05 versus control
0
10
20
30
40
Control ASA Clopidogrel Clopidogrel
plus ASA
D
N
A

s
y
n
t
h
e
s
i
s

(
x

f
o
l
d

i
n
c
r
e
a
s
e
)
*
*

27. Clinical Efficacy of Clopidogrel
Trial Patients Design Maximum
follow-up
Number of
patients
CAPRIE
1
Myocardial infarction,
stroke, peripheral
arterial disease
Clopidogrel
vs ASA
3 years 19,185
CURE
3
Acute coronary
syndrome
†
Clopidogrel
*
vs placebo
*
1 year 12,562
CLASSICS
2
Coronary stenting Clopidogrel
*

vs ticlopidine
*

4 weeks 1,020
1. CAPRIE Steering Committee. Lancet 1996; 348: 1329–39. 2. Bertrand NE et al. Circulation
2000; 102: 624–9 3. The CURE Trial Investigators. N Engl J Med 2001; 345: 494–502.
Clinical Benefit of Clopidogrel in more than
30,000 Patients – from CAPRIE to CURE
*
On top of standard therapy (including ASA)
†
Without ST segment elevation

28. COX (cyclo-oxygenase)
ADP (adenosine diphosphate)
TXA
2
(thromboxane A
2
)
CLOPIDOGREL
ASA COX
ADP
ADP
C
GPllb/llla
(Fibrinogen receptor)
Collagen thrombin
TXA
2
Activation
TXA2
ASA
Synergistic Mode of Action with
Clopidogrel and ASA
1
1. Schafer AI. Am J Med 1996; 101: 199–209.

29. Synergistic Action of Clopidogrel
on top
of ASA in Thrombus Formation
1
1. Herbert JM et al. Thromb Haemost 1998; 80: 512–18.
-100
-80
-60
-40
-20
0
0 5 10 15 20 25 30 35 40 45 50
Time (minutes)
B
l
o
o
d

f
l
o
w

(
%

d
e
c
r
e
a
s
e
)
Clopidogrel plus ASA
(10 mg/kg plus 10 mg/kg)
Clopidogrel (10 mg/kg)
ASA (10 mg/kg) Placebo
Experimental model

30. Synergistic Action of
Clopidogrel on top of ASA in
Thrombosis
1
1. Makkar RR et al. Eur Heart J 1998; 19: 1538–46.
Control (unperfused)
Thrombus weight 20 mg
ASA 10 mg/kg IV
Thrombus weight 18 mg
Clopidogrel 5 mg/kg IV
Thrombus weight 8 mg
Clopidogrel 5 mg/kg IV plus ASA
10 mg/kg IV Thrombus weight 1 mg
Stent model

31. GP IIb-IIIa ReceptorGP IIb-IIIa Receptor
White HD. Am J Cardiol. 1997; 80(4A):2B-10B.
Final common Final common
pathway to pathway to
platelet platelet
aggregationaggregation

32. Structure of the GP IIb/IIIa Site

33. Coller. Coller. Heart Disease, Update 4. Heart Disease, Update 4. 1995.1995.
Platelet GP IIb/IIIa Receptor in
Vascular Injury: Adhesion and
Activation
PlateletPlatelet
GP IIb/IIIaGP IIb/IIIa
GP Ib-IX-VGP Ib-IX-V
EndotheliumEndothelium
von Willebrand factorvon Willebrand factor
GP Ia/IIaGP Ia/IIa
CollagenCollagen
Fibrinogen Fibrinogen
(or von (or von
Willebrand Willebrand
factor)factor)GP IIb/IIIaGP IIb/IIIa
ActivationActivation
AdhesionAdhesion

34. Coller. Coller. Heart Disease, Update 4Heart Disease, Update 4. 1995.. 1995.
Platelet GP IIb/IIIa Receptor in
Vascular Injury: Aggregation
Fibrinogen Fibrinogen
(or von Willebrand factor)(or von Willebrand factor)
``
GP IIb/IIIaGP IIb/IIIa
AggregationAggregation

35. RestingResting
PlateletPlatelet
Receptors inReceptors in
ligand-unreceptiveligand-unreceptive
statestate
GP IIb/IIIa
Receptor Inhibitor
Inhibition ofInhibition of
Platelet Platelet
AggregationAggregation
Activated PlateletActivated Platelet
Receptors in ligand-Receptors in ligand-
receptive statereceptive state
FibrinogenFibrinogen
AggregatingAggregating
PlateletsPlatelets
GP IIb/IIIa receptors occupied by fibrinogenGP IIb/IIIa receptors occupied by fibrinogen
which forms bridges between adjacent plateletswhich forms bridges between adjacent platelets

36. André P et al. Circulation. 2002;106:896-9.
Activated plateletUnstimulated platelet
GP IIb/IIIa antagonists block
sCD40L release from platelets

37. GP IIb/IIIa + PCI
≥80% occupancy
GP IIb/IIIa + No PCI
<80% occupancy
>12 hours
Antman EM. Am Heart J. 2003;146(suppl):S18-22.
Proposed model for optimal use
of GP IIb/IIIa inhibitors

38. Furman MI et al. J Thromb Haemost. 2005;3:312-20.
Giugliano RP, Braunwald E. J Am Coll Cardiol. 2005;46:906-19.
Potential mechanisms for reduction
of thrombo-
inflammation with GP IIb/IIIa
inhibition
•Inhibit platelet activation
•Reduce sCD40L in ACS and PCI
•Blunt CRP increase in ACS and PCI
•Reverse endothelial dysfunction induced by PCI
•Reduce leukocyte-platelet aggregation in ACS

39. Gp IIb/IIIa ANTAGONISTS
•Platelet Gp IIb/IIIa receptors play a pivotal
role in platelet-mediated thrombus
formation, binding to binds to fibrinogen
and vWF
•IIb/IIIa antagonists differ in receptor affinity,
reversibility, and specificity

40. Abciximab
•Human/murine chimeric monoclonal
antibody Fab
•K
D
5 nmol/L
•Indication: PCI

41. Eptifbatide
•Cyclic peptide
•K
D
120 nmol/L
•Acute coronary syndrome

42. Tirofiban
•Nonpeptide
•K
D
15 nmol/L
•Indication: acute coronary syndrome

43. Antman EM et al. Am Heart J. 2003;146:S18-S22.
Death or MI at 30 days
*Does not include 345 patients In the tirofiban only
group, which was stopped prematurely
Efficacy of GP IIb/IIIa inhibition
on death or MI in PCI or ACS
EPIC 2099
IMPACT II 4010
EPILOG 2792
CAPTURE 1265
RESTORE 2139
EPISTENT 2399
PRISM 3231
PRISM-PLUS 1570*
PARAGON 2282
PURSUIT 10,948
Overall 30,366
Trial N
Odds ratio (95% CI)
Favors
GP IIb/IIIa
Favors
placebo
1 2
0.79 (0.73–0.85)
P < 10
–9
Elective PCI
ACS
0

44. Special Mention

45. Colwell JA, Nesto RW. Diabetes Care. 2003;26:2181-8.
Altered platelet functions in
diabetes
¯ Membrane fluidity
Altered Ca
+2
and Mg
+2

homeostasis
­ Arachidonic acid
metabolism
­ Thromboxane A
2

synthesis
¯ Prostacyclin production
¯ NO production
¯ Antioxidants
­ Activation-dependent
adhesion molecules
(eg, GP IIb/IIIa, P-selectin)
These changes contribute to increased platelet
aggregability and adhesiveness in diabetes

46. Lincoff AM et al. Circulation. 2000;102:1093-100.
30-day death or MI
No diabetes
Diabetes
0.33 1.0 3.0
Placebo betterEptifibatide better
PURSUIT: Outcomes in diabetic
vs nondiabetic US patients
Odds ratio (95% CI)

47. Bleeding
risk
Thrombotic
risk
Will any drug ever prevent thrombosis without causing
bleeding ?