Anti - platelet drugs were decribed well in this PPT for the B.Pharm students who is learning medicinal pharmacology

1. M.Asiyabi
M.Pharm-1st year
Department of pharmacology

2. Historical background
• Platelets were discovered by G.Bizzozero in
1882.
• But, drug industry did not recognise them as
viable drug targets till 1960.
• Initially, researchers focused on clotting time
and also in thrombocytopenia.
• In 1960, focus shifted to interaction of
platelets with adhesion and aggregation.

3. Terminologies
• Thrombus : a blood clot formed in situ within the
vascular system of the body and impeding blood
flow.
• Embolus : a blood clot, air bubble, piece of fatty
deposit, or other object which has been carried in
the bloodstream cause an embolism.
• Venous thrombosis : a blood clot (thrombus) that
forms within a vein
• Deep vein thrombosis : a blood clot in the deep
veins of the leg
• Pulmonary embolism : a blood clot in the lungs.
• Arterial thrombosis : a blood clot that develops
in an artery

4. Etiology
• Arterial and venous thromboses are major
causes of morbidity and mortality rates.
• Deep-vein thrombosis (DVT) leads to
pulmonary embolism (PE).
• This triggers platelet aggregation and fibrin
formation leading to generation of a platelet-
rich thrombus that can temporarily or
permanently occlude blood flow.

5. • Arterial thrombi are rich in platelets because
of the high shear in the injured arteries.
• In contrast, venous thrombi (low shear
condition) contain relatively few platelets and
are predominantly composed of fibrin and
trapped red cells.

6. Action of Thrombin
• Release from endothelium (NO, PGI2 , von
vilebrand etc)
• Prothrombin to thrombin
• Activation of platelets
• Factor V to Va and factor VIII to VIIIa
• Fibrinogen to fibrin

7. Epidemiology
• > 2.5 million of deep vein thrombosis per year
• > 600,000 cases of pulmonary embolism every year
• > 50,000 deaths from pulmonary embolism
• > 11,000 post surgical PE every year

8. Rationale for Anti-thrombotic drugs
Vascular injury
Platelet adherance
and activation
Thrombin generation
and fibrin formation
Plasmin generation
and fibrinolysis
Reduce risk
factors
Platelet
inhibitors
Anti coagulants
Fibrinolytic drugs
THROMBOGENESIS THERAPHY

9. 1
• ANTI-PLATELET DRUGS
2
• ANTI-COAGULANTS
3
• FIBRINOLYTICS
ANTI-THROMBOTIC DRUGS

10. TREATMENT STRATEGY
• Strategies to inhibit or treat arterial thrombosis
focus mainly on antiplatelet agents.
• Anticoagulants are the mainstay of prevention
and treatment of venous thromboembolism
(because fibrin is the predominant component)
• Fibrinolytic therapy is used in selected patients
with venous thromboembolism.(Massive PE)

11. ANTI - PLATELET AGENTS
“Drugs which interfere with platelet function
and are useful in prophylaxis of
thromboembolic disorders”

12. ROLE OF PLATELETS

17. Antiplatelet drugs target various
steps in this process.

18. Anti-platelet drugs
Acetylsalicylic
acid (aspirin)
P2Y12
antagonists
GPIIb/IIIa
antagonists
Dipyridamole

19. Newer anti-platelet drugs
• Ticagrelor
• Thrombin Receptor Blockers : Vorapaxar

20. ASPIRIN
(Acetyl salicylic acid)
• The most widely used antiplatelet agent
worldwide is aspirin.
• Maximal effective dose : 50-320 mg
• At high doses (1 g/d), it also inhibits COX-2
(responsible for synthesis of prostacyclin, a
potent inhibitor of platelet aggregation)
• So, Higher doses are potentially less efficacious
and also increase toxicity, especially bleeding.

21. Aspirin blocks production of TxA2 by
acetylating a serine residue near the active
site of platelet cyclooxygenase-1 (COX-1).
ASPIRIN – MECHANISM OF ACTION

23. Side Effects
• Dose related side effects
- Dyspepsia
- Erosive gastritis
- Peptic ulcers
with bleeding and perforation.
• Hepatic and renal toxicity are observed with
aspirin overdose
• The risk of bleeding is increased when used
with warfarin.

24. Major drawbacks
• Allergic reactions - History of aspirin allergy
characterized by bronchospasm.
• Is not a very effective antithrombotic drug but is
widely used because of its ease of use
• Lack of response in some patients (aspirin
resistance)
• The irreversible platelet inhibition.

25. Dipyridamole
Properties other than anti-platelet activity :
• Dipyridamole is a potent coronary vasodilator.
• It has minimal effect on BP and cardiac work.
MECHANISM OF ACTION ON NEXT SLIDE

26. - It interferes with platelet function by decreasing the
metabolism of cAMP to 5’ AMP By inhibiting cyclic nucleotide
phosphodiesterases ( involved in metabolism of cAMP).
- It also inhibits Adenosine deaminases

27. Therapeutic uses
• The drug has little or no benefit as an
antithrombotic agent.
• So It is used in combination with warfarin.
• In the prophylaxis of coronary and cerebral
thrombosis of post-MI and post-stroke
patients.
• In patients with Prosthetic valves (artificial
heart valve) - it inhibits embolization.
• Dosage : 150 to 300 mg given BD

28. Adverse effects
• Exacerbation of Angina
• Headache
• Tachycardia
• GI distress.
DRAWBACKS :
1. Dipyridamole also has a vasodilatory effect and
should be used with caution in patients with severe
coronary artery disease;
2. chest pain may be aggravated in patients with
coronary artery disease who are receiving dipyridamole

29. Ticlopidine and Clopidogrel
• ADP antagonists, inhibit binding of Adenosine di
phosphate (ADP) to its receptors irreversibly
• Also Inhibit fibrinogen induced platelet
aggregation with out modifying GPIIb/IIIa
• Synergistic action with aspirin
• Both are prodrugs have long duration of
antiplatelet effect
• Clopidogrel a congener of ticlodipine is safer and
better tolerated.

30. MOA - ADP Antagonists

31. Adverse effects
Ticlopidine (Dose : 250 mg BD)
– Diarrrhoea, vomiting, abdominal pain
– Headache, tinnitus, skin rash
– Bleeding, neutropenia, thrombocytopenia
Clopidogrel (Dose : 75 mg OD)
– Implantation bleeding
– Less bone marrow toxicity
– Diarrhoea, epigastric pain, rashes

32. Clopidogrel resistence
• This variability is because of genetic polymorphisms
in the Cytochrome P450 (CYP2C19*2) isoenzymes
involved in the metabolic activation of clopidogrel.
• This is important because 25% of whites, 30% of
African Americans, and 50% of Asians carry the loss-
of-function allele.
• This will render them resistant to clopidogrel.
• So to such patients , prasugrel or newer P2Y12
inhibitors may be better choices.

33. Prasugrel
• It is also prodrug.
• Its onset of action is more rapid than that of
ticlopidine or clopidogrel.
• It produces greater and more predictable
inhibition of ADP-induced platelet
aggregation.
• It has prolonged effect after discontinuation
• Therefore problem araises if patients require
urgent surgery.

34. Cont…
• Contraindication : those with a history of
cerebrovascular disease (high risk of
bleeding).
• Caution : in patients weighing <60 kg or in
those with renal impairment.
• Dose : loading dose is 60 mg, and is given
once daily at a dose of 10 mg.

35. Glycoprotein IIb/IIIa Inhibitors
• Glycoprotein IIb/IIIa is a platelet-surface integrin.
• Glycoprotein IIb/IIIa is inactive on resting
platelets.
• It undergoes a conformational transformation
when platelets are activated by thrombin,
collagen, or TxA2 which endows GP with the
capacity to serve as a receptor for fibrinogen and
von Willebrand factor.
• Thus, inhibitors of this receptor are potent
antiplatelet agents.

36. Drugs (GP IIa/IIIb inhibitors)
• Newer potent platelet aggregation inhibitor
-Abciximab,
-Eptifibatide and
-Tirofiban

37. Abciximab
• It is is the Fab fragment of a humanized
monoclonal antibody.
• It also binds to the vitronectin receptor on
platelets, vascular endothelial cells etc..
(Vitronectin is a GP present in serum)
• Dose : 0.25-mg/kg bolus followed by
0.125 g/kg/min for 12 hours.
• Side effect : Bleeding, Haemorrhage,
Thrombocytopenia, paralytic ileus, constipation.
• Drawback : Expansive

38. Newer Anti-Platelets (Ticagrelor)
• It is an orally active, reversible inhibitor of
Purinergic receptor (P2Y12) – a G protein
coupled receptor.
• Dose : 90 mg tablets are available.
• When compared with clopidogrel, ticagrelor
produced a greater reduction in
cardiovascular death, MI, and stroke.
• It has a more rapid onset and offset of action.

39. Vorapaxar
• It is an orally active, high-affinity, potent and
competitive reversible antagonist of protease
activated receptor (PAR-1)
• So it blocks thrombin-mediated platelet
activation.
• Dose :Tablet 2.08 mg with Aspirin/ Clopidogrel
daily.
• Indications : To reduce thrombotic cardiovascular
events in patients.
• Adverse effect : Bleeding, depression, anemia.

40. Drug screening methods
1.In-vitro methods
Assay methods
Washed platelet
method
Whole blood
aggregometry
Platelet
function
analyser
2.In-vivo methods
Model of corotid
artery occlusion
in dogs
Photochemically
induced thrombosis
model in rats
Studies of anti-
platelet efficacy in
rhesus monkeys
Anti-platelet
efficacy in baboons
3.Ex-vivo method

41. Assay method – Born’s test
(Turbidimetry)
1. Selection of healthy volunteer blood donors
2. Preparation of platelets : Fresh blood from male
rabbit centrifuged at 250g for 10 mins to obtain
platelet-rich-plasma (PRP)
3. Assay method :
- Drug conc : 1-100 µM
- incubated with 0.25ml of platelet rich plasma for
1min
- followed by activation of platelet with various
agonist
- aggregation induced by ADP (100 µm), collagen
or thrombin

42. Cont…
• The inhibition of aggregation is expressed as
the percentage of the maximal rate of
aggregation observed in the absence of
antagonists.

43. Platelet function analyser (PFA)

44. PFA -procedure
• Blood sample is drawn and stored at RT with
citrated buffer solution.
• 800 µL containing test drug is placed into a
catridge.
• The test catridges simulate an injured blood
vessel in which the membrane coated with
type I collagen or ADP catridge.
• Blood is pipetted and aspirated thro a capillary
with negative pressure and thereby shear
forces is produced.

45. cont….
• Platelet aggregation is produced.
• Finally, a platelet plug occludes the apperture.
• The time measurewd in secs from beginning
of test untill formation of aggregates is called
closure time (measure of over all function of
platelets)

46. Ex-vivo method
• Acid soluble collagen (100 µg/kg) is injected
into the aortic arch of rabbits via carotid
artery.
• Platelet count is performed on blood
withdrawn subsequent to collagen
administration.
• The test drug is administered to the animal
before the collagen injection.

47. Photochemically induced thrombosis
model in rats
• Requirements :
- Animal : male wistar rats (230-320 gms)
- Anesthetic : Penobarbitol sodium
- Test drug
• Jugular vein cannulation
• Microvessels in the mesentry are observed
under trans illumination with halogen lamp.
• Thrombus formation is induced in the
microvessels by filtered light of wavelength
420-490 nm.

48. Procedure
• Test drug administered as i.v bolus into jugular
vein of a rat.
• Irradiation is started after 1 mins and flourescein
sodium (2.5% w/v) is injected.
• Whole process is monitored with TV camera
• The time when the thrombus begins to form
(time of initiation) and time when blood flow
completely stops (time of occlusion) are used to
determine ant-platelet activity.
• Rats are sacrificed at the end of experiment by
overdose of KCl.